US 3629731 A
Description (OCR text may contain errors)
United States Patent  inventor George J. Frye Portland, Oreg.
 Appl. No. 744,491
 Filed July 12, 1968  Patented Dec. 21, 1971  Assignee Tektronix, Inc.
 SAMPLING SYSTEM 29 Claims, 10 Drawing Figs.
 U.S. C1 333/7, 307/235, 307/259, 328/151, 333/31 R, 333/84 M  lnt.Cl 1101p 5/12, 1101p 3/08,1-103k 5/13  Field 01 Search 340/173;
 References Cited UNITED STATES PATENTS 2,751,558 6/1956 Grieg et a1. 333/84X 3,241,076 3/1966 Magleby et a1. 328/151 3,259,860 7/1966 Ayer 333/84 3,274,459 /1966 Sterzer 333/84 X 3,278,763 10/1966 Grove 333/7 X 3,308,352 3/1967 l-lutchins et al.... 328/151 X 3,417,294 12/1968 Steidlitz... 333/84 X 3,445,793 5/1969 Biard 333/34 3,475,700 10/1969 Ertel 333/7 3,184,674 5/1965 Garwin 333/84 X OTHER REFERENCES Primary Examinerl-lerman Karl Saalbach Assistant Examiner-Marvin Nussbaum AttorneyBuckhorn, Blore, Klarquist and Sparkman ABSTRACT: A sampling system for providing a sample of a high-speed input signal for display on an oscilloscope includes a transmission line to which the input signal is applied. The transmission line includes a pair of semiconductor diodes which are rendered nonconducting at a selected time for isolating a section of transmission line therebetween and temporarily storing a sample of the input signal. Output means connected to the transmission line between the diodes couples the sample to a cathode ray tube displiay means.
PREAMFLIFIER SAMPLING SYSTEM BACKGROUND OF THE INVENTION A sampling oscilloscope is an instrument which visually reproduces a high frequency input signal in the form of an output signal of much lower frequency, but having substantially the same waveform as the input signal. For accomplishing such a portrayal, a sample may be taken of a different portion of the input signal waveform during successive repetitions thereof and such samples may then be displayed successively on an oscilloscope.
Although the sampling apparatus in a conventional sampling oscilloscope generally employs semiconductor diodes or the like, in many cases the switching speed of the diodes is potentially much faster than the actual rise time of samplers using the diode. Present diode gate configurations carry a sampling diode through a complete tum-on-turn-off cycle, with sampling taking place while the diode is in the on condition. Unfortunately, the sampling speed is then a function of the waveshape of the sampling pulse or strobe pulse applied to turn the diode on and off, and frequently the diode is never turned very far on or into a low resistance condition before the sampling pulse must conclude. As a result, the speed of the sampler is somewhat limited, and the rise time of the sampler is not well determined.
SUMMARY OF THE INVENTION According to the present invention, a sampling system takes advantage of the rapid switching time of a gating means from a first conducting condition to a second condition. For example, the sampling may take place in response to the rapid switching of a semiconductor diode from an on condition to an off condition. Not only is the attainable speed of the sampler increased because of the rapid switching of the diode or the like, but also the rise time of the sampler is well determined and predictable. Only a portion of the sampling pulse or strobe pulse is effective in bringing about a sampled output. When, for example, sampling is accomplished by the shutoff of a semiconductor diode, only the trailing edge of the sampling pulse or strobe pulse is effective to bring about sampling action. Therefore, sampling is more accurate, and less demand is made upon the generator of sampling pulses or strobe pulses. Moreover, in the instance of the semiconductor diode, a lower resistive condition for the diode is attained when on, insuring a better charge collection efficiency and lower noise. The same noise performance is attained as with a system having an approximately 2% times slower response.
According to the system of the present invention, the input waveform to be sampled is applied as an input signal to a transmission line, to which output means for receiving sampled signals is also coupled. A gating means, for example a semiconductor diode means, is disposed between the input and output of the transmission line, and this gating means is effective to disconnect the portion of the transmission line coupled to the output. As a result, a sample of the input signal is effectively stored on the disconnected portion of the line, which sample may be coupled through output means to an oscilloscope or the like.
It is accordingly an object of the present invention to provide an improved sampling system for higher speed sampling.
It is a further object of the present invention to provide an improved sampling system for taking advantage of the potential switching speed ofa gating means or diode.
It is a further object of the present invention to provide an improved sampling system which accomplishes sampling in response to oneway switching action of a semiconductor diode or the like. 1
It is another object of the present invention to provide an improved sampling system having greater charge collection efficiency and lower noise.
It is another object of the present invention to provide an improved sampling system wherein the rise time thereof is well determined and predictable.
It is a further object of the present invention to provide an improved sampling system which is less dependent upon variations in diode characteristics and sampling or strobe pulse signals than sampling systems heretofore utilized.
It is another object of the present invention to provide an improved sampling system resulting in more uniformity in collection of charge over wide variations in ambient conditions.
The subject matter which I regard as my invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. The invention, however, both as to organization and method of operation, together with further advantages and objects thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings wherein like reference characters refer to like elements.
DRAWINGS FIG. I is a representation of a first sampling system according to the present invention;
FIG. 2 is a schematic drawing of a second sampling system according to the present invention;
FIG. 3 is a schematic drawing of an improved variation of the FIG. 2 system further providing improved blowby correction;
FIG. 43 is a plan view ofa preferred embodiment of the FIG. 3 device, and further including a schematic diagram of circuitry for operating the same;
FIG. 5 is a schematic drawing of a third embodiment of the device according to the present invention;
FIG. 6 is a schematic illustration of a generalized version of the FIG. 5 device;
FIG. 7 is a block diagram of a sampling oscilloscope of the type used with a sampling system according to the present invention',
FIG. 8 is a partially broken away plan view of a device according to the present invention supported in a holder therefor;
FIG. 9 is a cross section of the FIG. 8 device taken at 9-9 in FIG. 8; and
FIG. 10 is a partial cross section of the FIG. device taken at 10-10 in FIG. 8.
DETAILED DESCRIPTION Referring to the drawings, and particularly to FIG. I, a first sampling system according to the present invention includes a coaxial transmission line 10 having an input end generally designated at 12 to which a source of high frequency repetitive signals may be connected, and a resistive termination Id at the opposite end thereof. The resistive termination has a value equal to 2,, that is, the characteristic impedance of the line. The line comprises an outer conductor II and a central conductor 16 extending from the input end to termination 14, with central conductor I6 serially including first and second switching means or gating means 18 and 20 spaced therealong. These switching means or gating means thus set offa portion 22 of the line from the remainder thereof. Output means, here comprising a conductor 24, is tapped upon por tion 22 of the line, and this output means suitably includes an isolating element 26 in series therewith. The isolating element may consist of switching or gating means, or may comprise a resistor having a relatively large value of resistance whereby the output means will not present too great a discontinuity to the transmission line. The output means suitably couples to a preamplifier (not shown in this figure) which in turn provides an output for an oscilloscope circuit.
In operation, a high frequency input signal is provided at end I2 of the transmission line between central conductor I6 and outer conductor 11, usually for a predetermined period of time. With gating means 18 and 20 in a closed or conducting condition, the input signal propagates down the line and is absorbed by the Z, termination. Generally, the preamplifier con nected to output conductor 24 has a response which is slow relative to the input signals positive and negative variations, and moreover, is coupled to the transmission line by means of isolating element 26 which is suitably either an open switch or a relatively high resistance. Furthermore, the input signal is suitably applied for only a relatively short time as compared with the response of the preamplifier, while being long enough to establish stable transmission conditions on the line. Therefore, the preamplifier is not operated to any appreciable extent by the signal coupled to the input end of the line.
However, gating means 18 and 20 are then opened for disconnecting portion 22 of the line from the rest of the line at times when sampling is to be accomplished. Thus, the gating means 18 and 20 may be opened during the occurrence of successive portions of a repetitive input waveform for which samples are desired. When the gating means 18 and 20 are opened, portion 22 of the line temporarily stores a relatively steady value of the input waveform corresponding to the value when the sampling occurred.
The rise time of the sampler is given as the time required for a wave to travel between gating means 18 and gating means 20. This is somewhat approximate and assumes that gating means 18 and 20 have no forward resistance when on, and can be turned off in essentially zero time. If an edge of a square wave signal is propagating down the line between gating means 18 and 20 at the time such gating means are turned off, and average DC level of the square wave will remain on portion 22 of the line after the trapped signal has made several excursions up and down portion 22. Actually, as soon as gating means 18 and 20 are opened, isolating element 26 may be turned on, whereby the output means is coupled to a preamplifier for, in effect, delivering an average value of the trapped signal to the preamplifier.
In the event that isolating element 26 is a resistor, it should have a resistance large in comparison with the Z of the line. A signal will be effectively delivered to the preamplifier if element 26 has a resistance R, and line portion 22 has a capacitance C, such that RC presents a time constant of the same order of magnitude as the preamplifier response or rise time. Thus, the period of temporary storage on the line is at least comparable to the response time of the preamplifier.
After sampling, and shortly before taking the next sample,
gating means 18 and 20 are turned on, and isolating means 26, I
if it comprises a switch, is turned off, whereby the input signal can once again propagate down the line to termination 14. Sampling is thus accomplished in the present system by temporarily isolating a length of transmission line which acts as a temporary storage element for the sample. Since the gating means 18 and 20 need only to be turned off in order to provide the sample, sampling is much more rapid and predictable.
Sampling means 18 and 20 may comprise suitable gating means such as semiconductor diodes or triodes. Each of these sampling means may receive a gating signal or strobe signal simultaneously applied to both by external means (not shown) at predetermined sampling times. Alternatively, sampling means 18 and 20 may comprise similarly poled semiconductor diodes rendered alternately conducting and nonconducting by a sharp sampling pulse or strobe pulse applied across termination 14. lt will be observed that an edge of this strobe pulse first actuates gating means 20 and then actuates gating means 18 as the strobe pulse propagates on the line from right to left in FIG. 1. The rise time of such a system is then twice the time required for a wave to travel between gating means 18 and 20, that is, the rise time is equal to the time for the input signal to traverse this distance plus the time for the switching or strobe wave front to traverse the same distance in the opposite direction.
Typically, gating means 18 and 20 are similarly poled diodes normally biased in the off condition. The sampling pulse or strobe pulse is applied to'the line for holding gating means 18 and 20 in an on condition for a predetermined period of time. Then, the strobe pulse or sampling pulse is turned off so portion 22 of the line will store a sample of the input signal. The capacitance of portion 22 of the line is normally much less than the input capacitance of the preamplifier to which output means 24 is connected. The DC charge stored on portion 22 I of the line transfers to the input capacitance of the preamplifier through isolating element 26 in the form of a resistor after sampling.
FIG. 2 illustrates an embodiment of the present invention provided with a configuration to achieve a balanced system. Referring to the drawing, a first transmission line 28 comprising a first coaxial cable is provided with an input signal at input end 30. The transmission line 28 comprises an outer conductor and an inner conductor and extends to a signal output end 32 which is suitably coupled in an oscilloscope system to a trigger generator or the like having an input impedance matching the characteristic impedance of line 28, e.g. 50 ohms. Approximately midway of line 28, second and third lines 34 and 36 are branched therefrom, wherein the inner conductors oflines 34 and 36 are connected to the inner conductor of line 28, and the outer conductors of lines 34 and 36 are joined to the outer conductors of line 28 to provide a substantially parallel connection of the transmission lines. Thus, an input signal applied at input end 30 of line 28 will not only propagate toward output end 32, but will also propagate to the left and right through lines 34 and 36 when the signal reaches thejunction.
Disposed in series with the central conductor of line 34 are semiconductor diodes 38 and 40 spaced from each other along the line by a distance of approximately L,. The diodes are poled in the same direction, that is, both having their cathodes oriented toward the central conductor of line 28. An output means including resistor 43 is connected to the central conductor of line 34 approximately midway between diodes 38 and 40.
Similarly, the central conductor of line 36 is provided with semiconductor diodes 42 and 44 serially located therealong and poled in the same polarity direction as diodes 38 and 40. That is to say, a DC voltage applied across all the diodes in series will cause all of the diodes either to conduct or not conduct, depending on the polarity of such voltage. Diode 42 is located approximately the same distance from the central conductor of line 28 as is diode 40, and furthermore, diodes 42 and 44 are spaced apart by a distance approximately equaling L,. Output means comprising resistor 46 is connected to the central conductor of line 36 approximately midway between diodes 42 and 44. The remaining ends of resistors 43 and 46 are coupled together via conductors and 82 to provide a sampling signal to a preamplifier, with a capacitor 48 being serially interposed in conductor 80 between resistor 43 and the common connection. Capacitor 48 provides coupling for the resistors as far as a sampled signal is concerned, while establishing DC isolation so that appropriate DC bias values may be applied to the diodes. Resistors 43 and 46 in a constructed embodiment had a value of about 16 K.
Strobe signals of opposite polarity are applied at end 50 of line 34 and end 52 of line 36, wherein the strobe pulses are supplied from generators having an output impedance matching the impedance of the line, e.g. approximately 50 ohms. As the strobe pulses are applied, input end 50 rises to a positive voltage from a negative voltage, while end 52 of line 36 drops from a positive voltage to a negative voltage. When the strobe pulses are on, it will be seen that the polarities thereof are in such a direction as to cause diodes 38, 40, 42, and 44 to conduct. The strobe pulses are somewhat longer than double the propagation time of the length of line, L For instance, the strobe pulses are typically picoseconds long, and may be repeated at intervals separated by a longer time, eg every ten microseconds. They also have very sharp trailing edges. While the strobe pulses continue, an input signal applied to input end 30 ofline 28 will propagate down both lines 34 and 36, but the input signals will not affect the preamplifier to a very large extent, eg because of the duration of the strobe of sampling pulses. The duration of the strobe or sampling pulses is desirably short as compared with the slower response desirably provided by the preamplifier, while being long as compared to the double transit time of the length of transmission line, L At the conclusion of the strobe pulses, all the diodes are rendered nonconducting, and the sample of the signal existing on lines 34 and 36 between diodes 38 40, and 42-44, respectively, will be stored as a charge for a relatively long period of time whereby the preamplifier can be responsive thereto. This charge will be transferred to the preamplifier through resistors 43 and 46.
The FIG. 2 embodiment of the present invention has the previously enumerated advantages, e.g. it is capable of high speed sampling, the typical repetition rate being approximately I00 kilohertz. The rise time is well determined and predictable. A low forward resistance is obtained from the diodes since the diodes may be changed from substantially a state of full conduction to a state of nonconduction, resulting in greater charge collection efficiency and lower noise. The same noise performance is attained as with a system having an ap proximately 2% times slower response. The system is not particularly sensitive to the strobe pulses so long as the turnoff dv/dt of the strobe pulses is rapid as compared with signal excursions, because only the turnoff time is important. The system of FIG. 2 provides additional advantages because of its balanced configuration. As a result of use of balanced opposite polarity strobe signals, there is less kick out of the strobe signal into the input signal channel, e.g. through input end 30 of line 28. For the same reason the preamplifier sees principally only the stored portion of the input signal rather than the strobe pulses. Furthermore, the balanced system is relatively independent of temperature effects on the diode operating characteristics.
In the operation of the embodiment of FIG. 2, the rise time for the sampling system is equal to twice the time required for a wave front to traverse the distance L,. As described in connection with the FIG. 1 embodiment, one such period is required for the signal to propagate outwardly from line 28 in lines 34 and 36 while an equal period is required for the strobe pulses to propagate inwardly by the same distance.
The embodiment of FIG. 3 is quite similar to the embodi ment of FIG. 2 wherein like elements are referred to by like reference numerals. This embodiment further includes input diodes 54 and 56, poled in the same direction as the other diodes, disposed between the central conductor of line 28 and diodes 40 and 42 respectively. A baising circuit, including resistors 58 and 60, provide a bias for diodes 54 and 56 such that the latter are normally nonconducting in the absence of the strobe pulses. Thus, resistor 58 couples the junction between the cathode of diode 40 and the anode of diode 54 to a first bias voltage by way of conductor 76, while resistor 60 couples thejunction between the cathode of diode 56 and the anode of diode 42 to a second bias voltage via conductor 78. Capacitors 62 and 64 are connected between the bias voltage points and ground to prevent signal cross-coupling through a power supply or the like. The bias voltages are selected such that the cathode of each diode is normally positive with respect to its anode, when the strobe signals are not present.
The purpose of the additional diodes 54 and 56 is to compensate for blow-by", which may be defined as the coupling of an input signal through the capacitance of diodes 40 and 42 into the preamplifier in the absence of a strobe signal. The insertion of the additional diodes 54 and 56, together with resistors 58 and 60, provides a first differentiation of such blow-by" input signal, while diodes 40 and 42, in combination with resistors 43 and 46, provide a second differentiation of the blow-by signal. Since a given signal excursion is doubly differentiated before it reaches the preamplifier, it will then have both positive and negative substantially equal excursions and will tend to have very little effect upon the preamplifier. Such signal is also quite attenuated. The construction and operation of the FIG. 3 embodiment is otherwise substantially the same as described in connection with the embodiment of FIG. 2.
FIG. 4 illustrates an advantageous construction for the system according to FIG. 3, wherein corresponding elements are referred to employing similar reference numerals. Referring to FIG. 4, the respective transmission lines are realized as strip lines including center conductors deposited on an insulating ceramic wafer 66 disposed between two grounded planar conductors 68 and 70 spaced on either side of the ceramic wafer and acting as the outer conductor for the transmission lines. The center conductors 26', 34', and 36 correspond to similarly numbered transmission lines in the FIG. 3 embodiment. The diodes 38', 40', 54, 56, 42', and 44' are very small, nonencapsulated semiconductor diode chips connected serially with strip line conductors 34' and 36'. These chips are relatively flat and are soldered onto the strip line conductors, while short leads connect from the diode junctions on top of the chips to the next section of strip line conductor, as illustrated. Resistors 43', 46', 56, and 60 are deposited or silk screen printed resistors connected in the same relative circuit positions as illustrated in FIG. 3. These resistors here somewhat overlap the ends of conductors 76', 78', and 82, which are deposited upon ceramic wafer 66.
The FIG. 4 embodiment further employs deposited guard conductors 72 and 74 connected by short lengths of wire to conductors 76' and 78' for breaking up the capacitances present on the ceramic wafer between conductors. The guard conductors 72 and 74 together with conductors 76' and 78 are connected to DC bias voltage points and are grounded for alternating currents through capacitors 62 and 64. They thereby break up the capacitance as may be present, for example, between center conductor 28 and deposited conductors 6t) and 82, and deter undesired coupling therebetween.
The input end of conductor 28 is connected to input jack 84, and the output end of conductor 28' is connected via output jack 85 and attenuator 86 to a trigger circuit for an oscilloscope or the like. Ends 50' and 52' of conductors 34' and 36 are connected respectively to a strobe circuit for producing positive-going and negative-going :strobe pulses. Ends 50' and 52 of conductors 34' and 36' are: also connected to taps on a voltage divider comprising resistors 92, 94, 96, 98, and potentiometer W0, interposed between positive and negative voltage terminals. Resistor 92 is connected between conductor end 50' and a negative voltage terminal, while resistor 94, potentiometer 100, and resistor 96 are serially disposed in that order between end 50' of conductor 34' and end 52 of conductor 36'. A resistor 98 is connected between conductor end 52 and the positive voltage terminal. The tap 1102 of potentiometer 100 is connected to a bias voltage, the potentiometer being used for balancing the circuit according to the present invention. The bias voltage may comprise feedback from the oscilloscopes sample envelope detector or memory as hereinafter described. The voltage divider provides a voltage across the series of diodes appropriate for normally holding the diodes in a nonconducting state.
A second voltage divider, comprising resistors 104, 106, 106, Ill), and M12, is connected between ends 50' and 52 of conductors 34' and 36. Conductor 76 is connected to the junction of resistors 106 and 108 while conductor 78' is connected to the junction between resistors 108 and 110. These junctions are also bypassed to the conductor ends 50' and 52 by means of capacitors 114 and H6, respectively. Conductor 80 is connected to thejunction between resistors I10 and 112 through an isolating resistor 120. The: resistors 43, 56, 60', and 46, coupled to respective locations along the transmission lines, are thus connected to points along the voltage divider, l04-l66-I08-l 10-1I2 so that each of the diodes, 38, 4t), 54', 56, 42', and 44', individually receives a voltage thereacross for biasing the diode to an off condition. However, when the strobe circuit generates its strobe output pulses, the voltage polarity across the voltage dividers is reversed such that each of the diodes then conducts.
when the strobe pulses conclude, the diodes are returned to their original nonconducting condition. However, isolating resistors H8 and are of sufficient value so that the temporarily stored values of the input signal on the portion ofconductors 34 and 36 to which resistors 43' and 46' are connected are not shorted out, but effectively appear across resistors 118 and 120 for coupling to preamplifier 122. Since the arrangement is symmetrical, the temporarily stored sample of input signal from conductors 80 and 82' will be substantially the same, but the strobe pulses will be balanced out. General operation of this embodiment is essentially the same as the embodiment of FIG. 3.
A more exact and detailed physical representation of a preferred form for ceramic wafer 66, together with the environment therefor, is illustrated in FIGS. 8 through 10, wherein like elements are referred to by like reference numerals. Wafer 66 is small, being on the order of one-half inch by three-eighths inch, and 0.015 inch thick. The spacing between a strip line conductor and planar conductor 70 or planar conductor 68 in the specific embodiment is approximately 0.025 inch. The double transit time of the length of transmission line, L, (eg between diodes 38 and 40'), is typically on the order of picoseconds. Thus, the lines are short and fast, making possible the storage and sampling of a very short portion ofinput signal.
The ceramic wafer 66 together with miniature diodes 38', 40, 54, 56', 42', and 44 and resistors 43, 46, 58', and 60, constitutes a hybrid integrated circuit wherein the diodes and resistors are nonencapsulated, thick-film" elements. As can be seen in the drawings, the diode and resistor components are small in comparison to the transmission line structure. Also, the diode and resistor components are essentially flat upon the ceramic wafer 66, such that these hybrid integrated circuit components themselves add very little capacitance to the system. Thus these components do not interfere with transmission line operation. The components also present very little discontinuity on the transmission line, assuming the diodes are conducting and assuming the resistance values of the resistors are large as compared with the characteristic impedance Z,,, of the line. MOreover, the diode and resistor components are physically and electrically connected directly to the strip line conductors, i.e. by zero or nearly zero length conductor leads, and therefore substantially zero lead delay is produced, thereby enhancing the speed of circuit operation. Because of the extremely short lead lengths resulting in minimum delay, and because of the low shunt capacitance produced by the components, the illustrated construction provides a fast dis tributed system which includes fixed components in the transmission line environment, wherein a high-speed signal may be received and operations may be rapidly performed thereon.
The construction of the present invention bridges. the gap between integrated-type circuitry and high speed input signals which may be advantageously applied thereto. The very small nonencapsulated and closely positioned components enhance the speed of the system while the strip line planar conductors 68 and 70 act to protect exposed delicate components and the ceramic wafer from damage.
Referring to FIGS. 8 through 10, ceramic wafer 66 in its preferred form includes a plurality of apertures or slits 160 extending therethrough which in effect separate the portions of lines 34 and 36' serially connected by diodes. The ceramic wafer 66 is suitably dry-pressed into the desired shape, including slits 160, and then fired. The ceramic material is preferred for the hybrid integrated circuit because of its excellent dielectric properties. The slits 160 reduce the capacitance between portions of lines 34 and 36', with the dielectric constant between line portions being reduced essentially to that of air. Capacitive coupling across .diodes 38, 40', 54', 56', 42, and 44' is thus reduced.
The ceramic wafer 66 is slidably supported in slot 162 provided in a unitary body or holder 164, inner surfaces 68' and 70 of which form the planar conductors spaced on either side of the wafer. Surface 70 is provided by an integral part of holder 164, while surface 68' is supplied by the inner side of an insert 166 brazed onto the body as indicated at 168 in the drawings.
The holder 164 including insert 166 is provided with cylindrical bores for receiving roll pins 172. The roll pins 172 pass through apertures 174 in wafer 66 and thus form means for releasably securing the wafer in the slot 162. The apertures 174 are somewhat larger than the roll pins whereby limited movement of the wafer 66 is permitted within the slot, even though the pins are in place, whereby the wafer may be finally positioned by spring fingers 176 upon a circuit board 178. These spring fingers contact the ends of conductors 76, 78', and 82' as well as ends 50 and 52' oflines 34' and 36', all of which extend around the edge of the wafer 66 so as to make suitable contact with the spring fingers. As can be seen from the drawings, conductors 76, 78, 80, and 82 are configured upon wafer 66 so as to avoid apertures 174 and roll pins 172.
The holder 164 includes corner flanges 180 provided with holes for receiving screws 182 employed for removably securing body 164 to circuit board 178 comprising part of a larger apparatus. For example, the apparatus may include the additional circuitry illustrated in FIGS. 4 and 7. Thus, these screws need only be loosened for removing the entire package from the apparatus, eg for replacement or servicing thereof. When the holder 164 is returned to. the circuit board, spring fingers once again make contact with the conductors at the edge of wafer 166, and finally position the wafer so that all the spring fingers make their correct contact.
Holder 164 includes end walls,184, between which insert 166 is secured, which are tapped to providejacks 84 and to receive coaxial cable connectors 190 and 192, respectively. Coaxial connectors 190 and 192 are provided with springloaded center conductors 194 and 196 for contacting the respective ends of line 28', which extend around the edge of wafer 66, at a time when connectors 190 and 192 are fully inserted in jacks 84 and 85. Jacks 84 and 85 are shouldered at 198 and 200 so that when the coaxial connectors are fully inserted against such shoulder, the most advantageous electrical transition is made between the coaxial cables and the strip line. It is also apparent that insertion of the coaxial cable connectors in jacks 84 and 85, wherein the coaxial cables include a grounded exterior conductor, effectively grounds the holder 164 with insert 166 whereby surfaces 68' and 70' provide outside grounded planes for the strip line configuration.
Although the ceramic wafer 66 is very small and the components supported thereon are quite delicate, being nonencapsulated to reduce their size and capacitance, the overall construction of holder 64 provides a protective, substantially shockproof, and substantially vibrationproof housing for the ceramic wafer and components. The holder may be handled itself as a regular component, and be inserted and removed from an apparatus wherever desired. Thus, the wafer and components are substantially enclosed and protected between inner surfaces 68' and 70 which provide the planar conduc tors for the strip line configuration, the components actually forming part of a transmission line system. The combination provides a mounting which allows a transmission line signal environment with insignificant reflection from discontinuities, and a transmission bandwidth extending beyond 18 GHz.
While the combination of a hybrid integrated circuit and a strip line as illustrated in FIGS. 8 to 10 is particularly useful for the purpose set forth, Le. a sampling system the same construction is applicable to other devices for receiving a high speed or high frequency signal into an environment which also employs fixed or lumped constant components.
FIG. 5 illustrates another embodiment of the device according to the present invention wherein one gating means 126 is employed for disconnecting transmission line 124 from signal input jack 136 at predetermined sampling times. The gating means 126 here comprises a diode bridge including a first pair of similarly poled diodes 132 and 134 having their midconnection coupled to jack 136, and a second pair of like poled diodes 128 and having their midpoint connected to a transmission line 124. The diode pairs are disposed in parallel and are normally biased in a nonconductive state so that no input signal is delivered through the gating means. However, when the strobe pulses are supplied with the polarity indicated in the drawing, the diodes are caused to conduct for coupling an input signal to transmission line 124.
Transmission line 124 may comprise any suitable form of transmission line, and has coupled thereto an output means here comprising resistor 138, desirably having a high value of resistance in comparison to a characteristic impedance of the transmission line. When the gating means 126 is opened by the strobe pulses, the signal input propagates along transmission line 124. The duration of the strobe pulses is fairly short as compared with the response of preamplifier to which resistor 138 is connected, but is long in comparison to the double transit time of the length of transmission line, L,, as in the case of the previous embodiment whereby stable transmission conditions are established on the line. As in the previous embodiments, the transmission line operates as a temporary storage element when the strobe pulses conclude, storing a sample of the input signal as was propagated down line 124 at the time the strobe pulses concluded. This sample will be stored long enough to operate the preamplifier to which resistor 138 is connected. The rise time is again twice the transit time for the length ofthe line, L,.
Although the bridge arrangement of diodes is preferred for gating means 126 in FIG. 5, because of added blowby compensation, it is understood that other gating arrangements may be employed. FIG. 6 illustrates a generalized arrangement wherein gate 126 is indicated in block diagram form, it being understood that various other forms of gating means may be utilized as known by those skilled in the art.
FIG. 7 illustrates an oscilloscope circuit employing a sampling system according to the present invention. The present invention corresponds to sampling gate block 140 in FIG. 7, to which an input signal is applied via terminal 148. When a selected triggering point of the input signal occurs, trigger circuit 88 generates a trigger pulse which is applied to fast ramp circuit 150. The fast ramp circuit initiates a fast-falling voltage ramp which is applied to one input of a slewed pulse generator and comparator 152. The other input to the comparison portion ofblock 152 is a staircase voltage from a staircase genera tor 154. Each time the fast ramp voltage falls to the level of the staircase voltage the comparator portion of block 152 ac tivates the slewed pulse generator. The slewed pulse generator in turn operates the strobe circuit associated with sampling gate 140 for producing sampling in sampling gate 140. At the same time, slewed pulse generator and comparator 152 steps the staircase voltage in staircase generator 154 by one increment. On the next triggering event, the fast ramp voltage must fall to the new level of the staircase voltage before a comparison can be made, thus increasing the delay between the triggering event and the generation of a slewed pulse from block 152. The length of time the slewed pulse is delayed from the triggering event depends upon the slope of the fast ramp and the level at which the staircase voltage is resting. Thus, in step fashion, the sampling gate is opened at successively later instants with respect to each initiating trigger, for the purpose of sampling different portions of different repetitions of the input signal.
Horizontal deflection voltages, derived from horizontal amplifier 156 is produced in response to the staircase voltage from staircase generator 154, which changes after each sample is taken, as previously explained whereby the spot on CRT 146 is moved horizontally for each sample.
The vertical channel of the FIG. 7 circuit includes the sampling gate 140 which takes quick samples of the input signal, and a sample envelope detectoror memory circuit 142 which remembers the level of each sample until another sample is taken. Block 142 receives the output of the preamplifier associated with the sampling gate. The output of block 142 is applied to the vertical CRT plates through vertical amplifier 144, and when the sample is taken, the dot displayed on the CRT screen is deflected to a vertical level proportional to the input signal level at the moment the input signal was sampled. The dot remains stationary on the CRT screen because of the memory action of block 142 until the next sample is taken.
Each subsequent triggering event initiates the same chain of events, but since the staircase voltage moves down one step each time, the fast ramp has to run down slightly farther each time before the comparator can produce a comparison pulse. ln this way, the sampling event is delayed by successively longer intervals and the samples are taken successively later along the input waveform with respect to the triggering point. Each time a sample is taken, the dot position on the CRT screen moves horizontally by one increment, and perhaps to a new vertical level. Since the sampling channel is an errorsensing circuit, the vertical position of the dot changes only if the input voltage level changes between sampling points. It is seen that the representation of the input waveform provided on CRT 1416 can be produced at a relatively low frequency input waveform.
The FIG. 7 circuitry is relatively well known, and is illustrated only for the purpose of explaining utilization of the present invention. It is understood that the present invention may also be employed with various other types of oscilloscope circuitry.
While 1 have shown and described preferred embodiments of my invention, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from my invention in its broader aspects. 1 therefore intend the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.
1. A system for providing samples of a repetitive input signal comprising:
a transmission line for receiving said input signal and for propagating said signal therealong,
output means coupled to said transmission line at a location therealong substantially different from the location where said input signal is applied,
and gating means, disposed between said locations, for
repetitively disconnecting the portion ofsaid transmission line coupled to said output means during selected repetitions of said input signal, and at different portions of different selected repetitions of said input signal to cause said portion of said transmission line to store samples of said input signal and deliver said stored samples through said output means when said portion of said transmission line is disconnected,
said portion of said transmission line coupled to the output means and disconnected by the gating means having a predetermined length,
wherein the rise time of said system for providing samples is determined according to the transit time of said transmission line portion.
2. The system according to claim 1 wherein said output means includes an impedance means coupled to said transmission line.
3. The system according to claim 1 wherein said gating means comprises a diode gate.
4. The system according to claim 1 wherein said transmission line is normally terminated substantially in its characteristic impedance.
5. A system for providing samples of an input signal comprising:
a transmission line having an input coupling portion for receiving said input signal,
output means for coupling to said transmission line at a lo cation therealong substantially different from said input coupling portion,
first and second switching means coupled in series with said transmission line on either side of said location where said output means is coupled,
and means for operating said switching means to isolate the portion of transmission line there'between and provide a temporarily stored output on said transmission line for said output means.
6. A system according to claim 5 wherein said output means includes an impedance coupled to said transmission line between said switching means.
7. A system according to claim 5 wherein said switching means comprise diodes.
8. A system according to claim wherein said transmission line is terminated in its characteristic impedance at a location on the remote side of said switching means from said input coupling portion,
9. A system for providing samples of an input signal comprising:
a first transmission line having an input coupling portion for receiving said input signal,
second and third transmission lines branched from said first transmission line and receiving said input signal from said first transmission line,
each of the branched transmission lines including first and second gating means disposed therealong in series therewith, and an output means coupled to each branched transmission line between the first and second gating means,
and means for operating said gating means for isolating the transmission line portions therebetween to provide a temporarily stored output for said output means. i
10. The system according to claim 9 wherein the output means for the second and third transmission lines are coupled together to provide a common output.
11. The system according to claim 9 including means for applying strobe signals to said second and third transmission lines on the remote side of said gating means from said first transmission line for first causing a period of conduction of said gating means followed by nonconduction thereof for isolating portions of the second and third transmission lines between gating means.
12. The system according to claim 11 wherein said gating means comprise like poled diodes.
13. The system according to claim 12 wherein said diodes are normally biased for nonconduction.
14. The system according to claim 12 further including an additional pair of diodes disposed serially between the first transmission line and the branched transmission lines similarly poled for enhancing blowby correction.
15. The system according to claim 9 wherein said transmission lines comprise coaxial transmission lines including said gating means in series with the central conductors thereof.
16. The system according to claim 9 wherein said transmission lines comprise strip lines including center conductors mounted on a common insulating wafer, and first and second planar conductors above and below said wafer in spaced relation therewith for completing the transmission line configuration,
said gating means comprising diodes mounted on said wafer in series with the center conductors of the branched lines.
17. The system according to claim 9 wherein said first transmission line extends beyond said branched transmission lines to provide a triggering signal for an oscilloscope employed for displaying said samples of said input signal.
18. The system according to claim 1 wherein said gating means is responsive to a strobe pulse for establishing a period of transmission line connection between said locations by said gating means, followed by the said disconnection thereof for a longer period of time during at least a substantial part of which said sample is stored on said portion of said transmission line.
19. The system according to claim 1 wherein said gating means comprises a diode bridge interposed between said locations, said diode bridge including a first pair of similarly poled diodes having their midpoint connected to a portion of said transmission line receiving said input signal, and a a second pair of diodes having the same polarity as the first pair when in the midpoint of the second pair of diodes is connected to the portion of said transmission line to which said output means is coupled, and means providing strobe signals to the terminals of said diodes remote from said transmission line for rendering the same conductive and then nonconductive.
20. The system according to claim 1 further including an amplification means for receiving samples of said input signal from said output means, and oscilloscope means for receiving the output of the amplification means for providing a display of the sampled input signal.
21. The system according to claim 20 wherein said gating means is responsive to a strobe pulse for establishing transmission line connection between said locations by said gating means followed by disconnection thereof,
said amplification means having a response of the same order of magnitude as the time constant which characterizes said output means together with the capacitance of said transmission line portion,
the period of transmission line connection being insufficient compared to the response of said amplification means for substantially operating said amplification means.
22. A system for providing a sample of an input signal comprising:
a transmission line for receiving said input signal and for propagating said signal therealong,
output means coupled to said transmission line at a location therealong substantially different from the location where said input signal is applied,
gating means, disposed between said locations, for connecting and then disconnecting the portion of said transmission line coupled to said output means to cause said transmission line to store said sample on the portion thereof coupled to said output means when the gating means disconnects such portion,
and amplification means for receiving said sample of the input signal from said output means, said amplification means being responsive to said sample primarily during the period of storage of said sample of said transmission line when said gating means disconnects said transmission line portion.
23. A device for coupling a high speed signal into an environment including fixed components comprising:
a planar insulating wafer provided with a plurality of conductors adhered thereto, at least one of said conductors comprising the center conductor for a strip line for receiving said high speed signal,
a pair of planar conductors substantially parallel to and disposed on either side of said wafer for completing a strip line configuration with at least said one of said conductor,
and a plurality of substantially planar components supported by said insulating wafer for providing immediate coupling between said conductors to form a hybrid integrated circuit therewith, said components being disposed between said planar conductors and having a thickness materially less than the spacing between said planar conductors and said wafer,
the said one of said conductors comprising the center conductor of the strip line being interrupted and immediately coupled by one of said components which comprises a substantially planar diode means for selectively isolating a portion of said center conductor,
and wherein another of said components is a substantially planar resistor means for immediately coupling said isolated portion to another of said conductors.
24. The device according to claim 23 wherein said wafer has an aperture coinciding with the interruption in said center conductor.
25. The device according to claim 23 including coaxial connector means for coupling a coaxial cable to said one of said conductors comprising the center conductor ofa strip line.
26. The device according to claim 23 wherein said wafer is formed of ceramic material.
27. A device for coupling a high speed signal into an environment including fixed components comprising:
a planar insulating wafer provided with a plurality of conductors adhered thereto, at least one of said conductors comprising the center conductor for a strip line for receiving said high speed signal,
a pair of planar conductors substantially parallel to and disposed on either side of said wafer for completing a strip line configuration with at least said one of said conductors,
and a plurality of substantially planar components adhered to said insulating wafer for providing immediate coupling between said conductors to form a hybrid integrated circuit therewith,
said components being disposed between said planar conductors and having a thickness materially less than the spacing between said planar conductors and said wafer,
said planar conductors being joined to provide a unitary body provided with a slot between said planar conductors for receiving said wafer within said body in spaced rela tion between said planar conductors, and including means for releasably securing said wafer in said slot between said planar conductors,
said device being further provided with connection means external to said wafer for making connection to the conductors adhered to said wafer, and means for removably securing said body to a larger apparatus.
28. The device according 18. claim 27 wherein at least one of said components are diode chips mounted on said center conductor and extending toward at least one planar conductor.
29, The device according to claim 27 wherein said means for releasably securing said wafer in said slot loosely holds said wafer so that said wafer is allowed limited movement within said slot, said wafer being positioned by said connection means when said body is inserted into an apparatus.
UNITED STATES PATENT orritt CERllFlCATE QURREQTWN Pat 3,529,731 Dated December 21, 1971 lnventor(s) GEORGE J FRYE It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
Col. 4, line 19, "conductors" should be =-=conductor- Col, 4, line 71, before "sampling" change "of" to --or- Col. 5, line 43, "baising should be biasing-- Col. 6, line 18, after "overlap" insert -=-the strip line conductors in making contact therewith and also overlap-- Col. 6, line 59, after "resistors" insert -l04= and 106 through an isolating resistor 118 while conductor 82' is similarly connected to the junction between resistors-- Col, 8, line 53, "reflection" should be --ref1ections-- Col, 9, line 56, after "156" insert move a spot on CRT 146 in step with the slewed pulse, Horizontal deflection voltage for horizontal amplifier 156- Col 10, line 12, before "input waveform" insert from successive samples of a much higher frequency-- in the claims:
Col, 11, line 63, delete the second "a" Col. 11, line 64, "when in" should be -wherein Col. 12, line 28, after "sample" change "of" to --on--- Col. 12, line 40, "ductor" should be -ductors- Col, 14, line 4%, "-18" should be --to-- Signed and sealed this 13th day of June 1972.
EDWARD M.FLETCHER,JR. ROBERT GOTTSCHA LK V Attesting Officer Commissioner of Patents FORM PO-1050(10-69) USCOMM-DC 60376-P69 fi us. GOVERNMENT PRINTNG OFFICE: I969 o-ass-aan