US 20100045864 A1
A transmission system for transmitting analog color video signals wherein a cable comprising multiple twisted pairs is employed, and certain of these pairs are coupled to carry selected color signals as a function of the delay provided by particular twist rates. In certain instances, selected signal delay devices are connected in circuit with certain twisted pairs. By such an arrangement, it has been found that relatively long distances between a computer and a monitor may be spanned by relatively low-cost, twisted pair cable commonly used for telephone communications.
1. A system for transmitting analog color video signals having color video components, comprising:
an interface to a cable having multiple twisted pairs, said pairs having varying twist rates relative to each other, said interface selectively coupling said pairs to carry selected ones of said color video components as a function of the varying relative twist rates.
2. A system according to
at least one transmitter to boost a signal strength of at least one of said color video signal components.
3. A system according to
at least two transmitters to boost signal strengths of corresponding ones of said color video signal components, said transmitters characterized by respectively differing gains.
4. A system according to
a cross switch to receive the color video signal components and apply the color video signal components to corresponding ones of the twisted pairs.
5. A system according to
6. A system according to
a computer to provide the analog color video signals having color video signal components.
7. A system according to
8. A system according to
9. A system according to
10. A system according to
11. A system according to
the color video components include a red, green, and blue component and a sync signal;
the cable includes four twisted pairs having respectively a first lowest relative twist rate, a second lowest relative twist rate, a third lowest relative twist rate, and a highest relative twist rate; and
said interface selectively couples the red component to said twisted pair having the first lowest relative twist rate, the green component to said twisted pair having the second lowest relative twist rate, the blue component to said twisted pair having the third lowest relative twist rate, and the sync signal to said twisted pair having the highest relative twist rate.
12. A system for receiving analog color video signals having color video components, comprising:
an interface to a cable having multiple twisted pairs, said pairs having varying twist rates relative to each other and carrying selected ones of said color video signal components, said interface imposing different relative signal delays on said color video components as a function of the varying relative twist rates.
13. A system according to
a connector coupled to the twisted pairs, and
a cross switch coupled to the connector to selectively re-impose said signal delays to different ones of said color video components.
25. A method of transmitting color video signals over a cable having a plurality of twisted pairs having varying twist rates, comprising the steps of:
ranking the twisted pairs according to their twist rates;
applying selected components of the color video signals to the twisted pairs in accordance with the ranking.
26. A method according to
applying a red component of the color video signal to a twisted pair having a lower relative twist rate.
27. A method according to
applying a green component of the color video signal to a twisted pair having a non-minimum relative twist rate.
28. A method according to
applying a blue component of the color video signal to a twisted pair having a non-minimum relative twist rate.
29. A method according to
applying a synchronization signal of the color video signal to a twisted pair having a highest relative twist rate.
30. A method according to
applying components of the color video signal to selected twisted pairs having the lowest relative twist rates.
31. A method according to
applying a red component of the color video signal to a twisted pair having a lower relative twist rate;
applying a green component of the color video signal to a twisted pair having a moderate relative twist rate;
applying a blue component of the color video signal to a twisted pair having a higher relative twist rate; and
applying a synchronization signal of the color video signal to a twisted pair having a highest relative twist rate.
32. A method of receiving color video signals over twisted pairs having non-uniform relative twist rates, comprising the steps of:
ranking the twisted pairs in accordance with their relative twist rates;
receiving components of the color video signals from different ones of the twisted pairs; and
delaying at least one component of the color video signals as a function of the ranking.
52. A transmission system for coupling video color signals including red, green, and blue video components to corresponding twisted pair communication lines, including:
a circuit to impose a discrete signal delay on at least one of the video components as a function of a discrete first rate in a corresponding one of said twisted pair communication lines.
This application is a continuation of application Ser. No. 09/294,591, filed Apr. 20, 1999 (which is incorporated herein by reference), which is a continuation of application Ser. No. 08/744,629, filed Nov. 6, 1996, now U.S. Pat. No. 5,926,509, issued Jul. 20, 1999 (which is incorporated herein by reference), which is a continuation-in-part of application Ser. No. 08/660,076, filed Jun. 3, 1996, which in turn is a continuation-in-part of application Ser. No. 08/177,442, filed Jan. 5, 1994, now abandoned. The said application Ser. No. 08/744,629 also claims the benefit of Provisional Application Ser. No. 60/010,741, filed Jan. 29, 1996, and is a continuation-in-part of application Ser. No. 08/741,697, filed Oct. 31, 1996, which is a continuation-in-part of application Ser. No. 08/219,979, filed Mar. 29, 1994, now U.S. Pat. No. 5,576,723, issued Nov. 19, 1996.
The invention relates generally to the transmission of wideband signals over relatively cheap, low-grade cable.
It is now commonplace to locate computers, keyboards, and monitors, particularly color monitors, at spaced locations in a building or buildings. These locations often are several hundred feet apart, requiring that where analog color signals are involved that there must be transmitted three separate color signals, each having an approximate frequency range from D.C. up to 200 MHZ. Thus, there is a requirement that appropriate transmission lines be in place, or be installed, to accommodate such transmissions. As is well known, either fiber optic or multiple coaxial cables may normally be employed, but such is often not available. Thus, there may be required by an occupant of a building that appropriate signal conductors be after fitted to the building. This can result in a considerable cost. Ideally, there would be present, or there might be installed at a relatively low cost, lower-grade conductors, such as network cable or twisted pair cable and that it be somehow used.
In a co-pending application, application Ser. No. 08/177,442, the existing cable was of the digital network type, for example, having 15 conductors within an outer shield and designed to carry on the order of 2,400 baud rate signals and wherein there existed straight (untwisted) conductors.
The problem in that case was to overcome frequency deficiencies and to overcome interaction between colors as finally received. The solution was that of discovering appropriate frequency-amplitude compensation plus effecting a phase reversal of one color signal appearing on one conductor (with respect to shield) and positioning this conductor between conductors carrying the other two color signals. At the receiver, the phase reversal was reversed back.
The present invention deals with a second type of cable, basically telephone (voice frequency) cable wherein there is included a plurality of twisted pair-type conductors, typically four pairs for the carrying of as many communications.
It too has unique problems with respect to frequency compensation. A second problem appears from the finding that different sets of twisted pairs, and in different cables, have a variety of twist rates, different twist rates for a given cable being provided to prevent telephone cross-talk between communications on different twisted pairs of a cable. Unfortunately, the applicants have found that the latter was a culprit in preventing good color signal transmissions since a composite of three color signals, sent on separate twisted pairs, is required, and the different twist rates of conductor pairs caused the lengths of the pairs and signal delays to differ. This in turn resulted in the receipt of a composite of color signals with observable impurities and thus an unsatisfactory presentation on a color monitor.
Significant, however, was the substantial availability of such cable and that it is already installed in many buildings where color transmissions were now needed. Thus, if it could be employed, such would enable a tremendous saving, a mark of clear technical achievement in view of the fact that the problem has remained unsolved for at least 10 years.
The applicants have discovered that relatively high frequency color video signals may be transmitted with high color purity over a cable having multiple, relatively low frequency, twisted pair telephone lines and despite their having different twist rates, which rates are non-uniform as between cable manufacturers. The applicants have solved the problem by effecting certain selected frequency compensation to color signals at each end of a cable and by discretely applying delays to the two twisted pair lines having lower twist rates. Alternately, in certain instances, applicants have discovered that adequate color purity can be achievable over cable runs of 300 feet or less by connecting the red video signals to the twisted pairs having the smallest twist rate (i.e., lowest twist rate), the green video signals to the twisted pair having the next highest twist rate, and the blue video signals through the twisted pair having the third largest twist rate. Typically, then, the synchronization signals would be connected through the cable having the largest twist rate (or tightest twist rate), which is not as critical.
These, as well as other objects and advantages of this invention, will be more completely understood and appreciated by careful study of the following more detailed description of a presently preferred exemplary embodiment of the invention taken in conjunction with the accompanying drawings, of which:
Referring initially to
Network 131, an impedance including a capacitive reactance, as will be described, is coupled from the input emitter 126 of transistor 117 to the emitter of transistor 123. Generally, in the Commander™ module, PNP transistor 117 is coupled in emitter-follower configuration and connected to network 131, with a base 120 of transistor 117 being coupled to a relatively weak analog video input signal. As such, collector 121 of transistor 117 is coupled to ground, providing an alternate current path to ground for the video signal. Resistor 128 of network 131 has a value of about 20 ohms, and capacitor 129 has a value of about 220 pF, network 131 serving to divert current in a direct relationship from the load impedance responsive to positive voltage excursions of the input signal applied to base 120. Impedance network 131 may be fixed to provide a generally fixed gain amplifier or one which can provide variable gains and in selected frequency ranges, the impedance including capacitive reactance and this reactance is coupled as shown between emitter 126 and emitter 125 of transistors 117 and 123. It is chosen to approximately equal the combined reactance effects of transistors 127 and 123 and a cable connected to a load 119. Collector 134 of transistor 123, as an example, is coupled across a load impedance 119 to the input of a conductor of a communications cable. As an example, for transistors 117 and 123, one may employ a transistor 2N2907a or equivalent, which is characterized by having a typical current gain of about 200 and is further able to maintain constant emitter voltage for a given base voltage. Typically, several reactance sets of RC may be employed, the choice being as to number and value for particular frequency ranges to be high frequency boosted, which in turn is a function of transistor effects of transistors 117 and 123 and the length of a cable.
A constant current source 136, which may be a conventional one, such as a fixed bias transistor, coupled to a stable voltage source, e.g., 4.5 volts, is coupled to terminal 140 between network 131 and emitter 119 and provides a current limited source of about 9.33 milliamps to be divided between network 131 and transistor 123. A voltage divider circuit 142 includes a resistor 144 coupled at one end to the 4.5-volt voltage source at terminal 138 and at an opposite end to terminal 152, also coupled to base 148 of transistor 123. A second resistor 150 is coupled at one end to a ground potential and at an opposite end to junction 152, with values of resistors 144 and 150 selected to provide a potential to base 148 of transistor 123 no lower than a highest anticipated peak input potential of the analog signal at the base of transistor 117, including any D.C., offset that may be present.
In the Commander™ module, it has been found that the analog video signal may be degraded to about 450 millivolts with a positive 150-millivolt D.C. offset. Thus, values of resistors 144 and 150 are selected to provide about 650 millivolts to terminal 152. With the described voltages applied to transistor 123, a lowest input signal at the input diverts current flow from transistor 123 to flow through resistor 128, reducing current flow through transistor 123 and the voltage at terminal 138 to a point where transistor 123 is biased in its operating range just above its cutoff point. As the input signal increases, current flow through resistor 128 decreases, slightly increasing a voltage level at terminal 140, biasing transistor 123 to a more conductive state and resulting in more current flow through transistor 123 and in turn increasing potential 107, for example, monitor 118, in direct relation with the input signal.
In the instance where the signal from source 108 is of lowered amplitude and is attenuated, but possesses sufficient current sourcing capabilities to drive network 131, the analog input signal is the input signal coupled directly to network 131, as represented by dashed line 154. In this configuration, resistors 144 and 150 are selected to provide a voltage at terminal 152 of about 650 millivolts below a highest anticipated peak input potential of the analog signal in order to compensate for elimination of the diode drop of transistor 117. Additionally, an output driver of routing circuit 108 would also be conventionally configured to provide an alternate current path to ground, as illustrated by ground 126. In this instance, when the input signal is at a lower state, current flows from current source 36 through network 131 to ground 127.
While the specific example described above which includes transistor 117 is an application tailored for the Commander™ module wherein the load is resistive in nature, a more generalized representation of the instant invention without transistor 117 may be illustrated where both load and bypass impedances are complex impedances. Theoretically, and assuming a transistor has a high current gain for transistor 123, the impedance of network 131 may be represented as Zb, with the analog signal source voltage represented by Vi, which in this instance, is coupled directly to load 119 (dashed line 154), and the highest excursion of the analog signal defined by Vx. Current through impedance Zb, is represented as I1. The voltage applied to base 148 is represented as Vf=Vx peak−0.650, and, as stated, is selected to be no lower than the highest peak amplitude of the input signal Vx minus the approximately 650-millivolt diode drop of the emitter-base junction of transistor 123. With such voltages applied to transistor 123, the voltage at junction 140 only fluctuates slightly due to the fixed base voltage and the forward biased emitter-base junction of transistor 123, with this slight fluctuation being sufficient to directly vary conductivity of transistor 123 and resultant current flow therethrough with respect to the input signal. This generally constant voltage at junction 140 is represented by Vx (max peak amplitude), with Ic being current from constant current supply 136. The load is represented by ZL, a complex impedance, with current flow through the load represented as I2 and voltage across load ZL represented as Vo. With such designations, voltage across the load is defined by:
and the constant current into junction 140 is a sum of the output currents, or:
The deflected current through impedance Zb is defined by:
with the inversely proportional flow of current through load ZL defined by:
and the voltage across the load defined by:
For a change of input voltage Vi,
which, when resolved, becomes:
yielding an A.C. gain of:
Thus, it is seen that gain of the amplifier is strictly controlled by load impedance and impedance between the emitters. In the specific example given for the Commander™ module, impedance of load Zb, is about 75 ohms resistive, the magnitude of impedance of network 131 at a D.C. potential is about 20 ohms, and at 30 MHZ, is about 0.6 ohms, as given by the generalized circuit analysis in the foregoing and familiar to anyone skilled in the art. Therefore, it is demonstrated that the above-described amplifier of the preferred embodiment possesses frequency sensitive gain which varies from a gain of about 75/20-3.75 (ZL divided by Zb,) at a D.C. level and a gain of about 75/0.6=125 at 30 MHZ. For the various embodiments illustrated and described hereinafter, the coupling impedance is first determined and gain calculated by dividing load impedance by the coupling impedance.
In operation, and referring to
As described, as the input signal fluctuates between low and high levels, the constant current is divided and fluctuates with the input-signal between transistors 117 and 123. In the absence of transistor 117, an analog video signal extending from about 150 millivolts or lower to about 600 millivolts is applied to network 131, and when at the lowest level, draws a highest level of current flow through network 131, which current flow applied to ground 126 reduces potential on emitter 119 to a level to bias transistor 123 to a higher impedance, reducing output on collector 134 to 0 volts. As the signal applied to network 131 increases, less current flows through resistor 128, increasing a potential at terminal 140 and biasing transistor 123 to a more conductive state in direct relationship with the input signal, shifting current flow to the load via transistor 123 and increasing voltage drop thereacross. In the event the input signal exceeds the reference potential applied to terminal 152, as by a noise spike, biasing transistor 123 into saturation, the load is generally protected from an over-voltage condition due to the constant current source 136 providing only 9.33 milliamps current flow to the load.
Referring now to
As shown, the three color signals are supplied to three like transmitter circuits 12, 14, and 16, one of which, circuit 12, is shown in detail. The synchronization signals SV and SH are supplied to time multiplexer 18 which conventionally time multiplexes these signals and provides a combined output signal S to an input of cross-switcher 34.
Referring first to transmitter circuit 12, the input signal SB, the blue video signal, is supplied by computer 10 to transmitter 12. Signal SB and the other color outputs of computer 10 each typically vary over a range from 0 to 750 my, and need frequency response up to about 200 MHZ.
Transistors Q10 and Q12 are coupled, as will be described, as a differential amplifier 26 providing high frequency boost. The emitter of transistor Q10 is biased through resistors R40 and R51 from the VCC and the VCC is decoupled at resister R51 by capacitor C19. The emitters of transistors Q10 and Q12 are connected by resistor R40 and by a series of RC high frequency boost filter circuits, as will be discussed below. The emitter of transistor Q12 is D.C. biased from the VCC through resistor R51.
The base of transistor Q12 is biased through resistor R39 from the VCC as effected by the load manifested at junction SJ1. A portion of this load is manifested from D.C. restorer 45 as driven by differential amplifier 26, shown in greater detail in
It is to be noted that this balanced output of differential amplifier 26 appears across the combination of transistor Q10 collector resistor R37 and transistor Q12 collector resistor R43.
As suggested above, and significantly, differential amplifier 26 provides several stages of high frequency boost as shown by RC circuits RC1-RC6 and C29, connected between the emitters of transistors Q10 and Q12.
The emitters of transistors Q10 and Q12 are also coupled by resistor R40, which is of a value of approximately 118 ohms and acts as the D.C. gain of the circuit.
High frequency boost stages RC1, RC2, and RC3, each consisting of a resistor and a capacitor in series, and each have a discrete time constant accomplished by sizing, of the capacitor of the stage to achieve a high frequency boost for different portions of the spectrum of interest from 0 to 200 MHZ.
In addition, there are provided three selectable high frequency boost stages, RC4, RC5, and RC6, each of which is switched in or out by a switch 56 shown in the open position. In operation, one or more of these switches would be closed as deemed necessary as a direct function of the length of cable to be used and as a function of the condition of the twisted pairs employed. Thus, RC4, RC5, and RC6 would additively be inserted as it appeared necessary to achieve the desired degree of signal purity at monitor 69 (
As shown in
The output of operational amplifier t32 is fed to the base input of transistor Q11, there being capacitor C28 connected between the base of it and ground, which capacitor is sized, e.g., 22 μF to 100 μF to stabilize the base voltage of transistor Q11. The emitter of transistor Q11 is connected to the base of transistor Q12 at summing junction SJ1, and the collector of transistor Q11 is grounded. As one function of transistor Q11, transistor Q12 receives a base voltage raised by a diode drop through transistor Q11, a like raise as provided by transistor Q9 to transistor Q10 (
Referring back to
Each of transmitter circuits 14 and 16 are identical with that of transmitter circuit 12, and thus together they apply blue (B), red (R), and green (G) input signals to discrete input ports P1-P3 of cross-switcher 24.
Multiplexer 18 time multiplexes the vertical and horizontal signals SV and SH from computer 10, and the resulting signal is applied as an input S to a discrete port P4 of cross-switcher 34. It has an output impedance of 100 ohms to match a twisted pair T4 of cable 57. Thus, in all, there are four signal inputs to cross-switcher 34.
Basically, cross-switcher 34 is configured to connect any one of its input signals at ports P1-P4 to any one of its output ports P0 1-P0 4, to which any particular pair of twisted pairs T1-T4 of a cable, having various arrangements of twisted pairs and twist rates, may be connected. Thus, as shown, cable 57, a common cable, has four twisted pair conductors, T1-T4, and these are connected to discrete output ports P0 1-P0 4 of cross-switcher 34. This enables the systematic employment of cable manufactured by a number of different manufacturers, with a variety of twist rates for individual twisted pairs to be selectively coupled, as will be described. Typically, all twisted pairs of a cable have twist rates which differ as between pairs, to prevent cross-talk in normal telephone usage.
Here, the magnitude of twist rate is used to designate cable pairs, this being from an examination wherein it has been found that cable pair T1 has the lowest twist rate, and cable pair T4 has the highest or largest twist rate. Applicants have determined that the connection pattern of cross-switcher 34 would be such that the S output of multiplexer 18 would be connected to a cable pair T4 of cable 57, it having the highest twist rate and thus the longest length. This follows from the determination that its twist rate and thus its inherent longest signal delay is not usually critical.
The B or blue output from transmitter circuit 12 would be connected to the twisted pair T3 having the next lower twist rate; the G or green output from transmitter circuit 16 would be connected to the next lower twist rate pair, T2. The R or red output of transmitter circuit 14 would be connected to the lowest rate cable pair T1 of cable 57 thus having the shortest overall length.
The relative twist rates of twisted pairs can be determined by a visual inspection of approximately six inches of the cable being examined, and therefrom connections would be arranged in terms of the foregoing system of connection.
The length of cable 57 would typically be in the approximate range of from 300 up to about 1,500 feet.
As a feature of this invention, for cables of a length of shorter than about 300 feet, the outputs would be directly connected to the same designated color inputs or receivers 74, 76, and 78 through cross-switcher 73, performing a like function to that of cross-switcher 34 as shown in parenthetically enclosed small letters. Also, as shown in
Demultiplexer 66 is fed an S signal from P0 4 of connector 67, and this signal is then. separated back into horizontal H and vertical V signals and to thus be directly applied to analog monitor 69.
For greater lengths, and as a further feature of this invention, the green and red signals are delayed. Thus, with this mode of operation, cross-switcher 73 is adjusted such that input P1, the red input, is connected to either the P0 2 or P0 3 output, and the green input at P2 is connected to the other of the P0 2 or P0 3 output. Input P3 of cross-switcher 73, the blue input, is connected to output P0 1. The position of particular color outputs of the cross-switcher are shown in capital letters B, G, and R. Delays units 61 and 63 are in circuit with the red and green signals, and the delay units are adjusted to compensate for the particular added lengths of twisted pairs T2 and T3 when compared with the length of twisted pair T1. Thereby, the time of arrival of the signals at monitor 69 can be adjusted so that all three signals arrive at the same time. There is, as shown, additional signal processing by receivers 74, 76, and 78, as will be further discussed below.
As shown in
Referring further to
Circuit connections are variably made for different delays by means of straps, for example, a strap 96, on each side of board 70 would connect in circuit any number of delay units D1, D2, D3, D4, and D5. Again, only the unit conductor terminals for the one side are shown, it being understood that the same designation and pattern of terminals and straps is provided on the opposite side, and the same pattern of strapping between units would be accomplished.
Thus, in order to employ a minimum delay, utilizing delay line D1, terminals 92 and 94 would be strapped together by a strap 96, whereby, as is apparent, only delay unit D1 would be in circuit between input and output signal lines 80 and 83 for a delay of 5 nanoseconds.
If it is desired to add another 5 nanoseconds of delay, straps 96 would interconnect terminals 92 and 102, and strap 106 would interconnect terminals 104 and 105. Following the same pattern of connection, if additional delay is needed, a strap would interconnect one of terminals 109, 111, 113, or 115, with an opposite terminal of terminals 110, 112, 114, or 116, and preceding straps would be employed in the fashion illustrated to further serialize delay units D3, D4, and/or D5.
As described, and referring to
The discrete outputs of cross-switcher 73 are connected, as shown, to the discrete balanced inputs of identical receivers 74, 76, and 78, receiver 74 being shown in detail. Examining receiver 74 (
Referring now additionally to
The emitters of transistors Q2 and Q1 are supplied current and bias control by control 130 (
Differential amplifier 110, which is basically formed by transistors Q2 and Q1, includes a high frequency boost circuit and wherein there are four serially-connected RC circuits RC7, RC8, RC9, and RC10, each circuit connected between the emitter of transistors Q2 and Q1 and each having a time constant to deal with discrete portions of the desired frequency response boost, from D.C. to 200 MHZ. Additionally, capacitor C8, also connected between the emitters of transistors Q2 and Q1, has a value of approximately 150 pF and functions to add selected high frequency boost as necessary and as a direct function of the length of transmission line.
As in this case, it is desired to obtain only a single-ended output of differential amplifier 110, a single load resistor, being R36, is connected between the collector of transistor Q2 and ground, and the collector of transistor Q1 is directly grounded. The output of differential amplifier 110, across resistor R36, is buffered through transistor Q7 (
As noted above,
Referring again more particularly to
To effect operation, a D.C. bias is applied from a VCC A.C. bypassed by capacitor C21, through resistor R35 to the emitter of transistor Q10 a and additionally through resistor R34 to the base of transistor Q10 a and collector of transistor Q7. The output of this amplifier or buffer stage at the connected emitter of transistor Q7 and collector of transistor Q10 is fed directly to monitor 69 and through resistor R33 to the base of transistor Q9 a of differential amplifier stage 71 of D.C. restoration circuit 124.
Differential amplifier 71 basically employs transistors Q9 a and Q8, and the emitters are connected together and biased by a +, or VCC terminal through resistor R16. The base of transistor Q9 a is biased through resistor R32 from a VCC terminal, and the base of transistor Q8 is biased through resistor R28 from the VCC. Resistor R27, bypassed by stabilizing capacitor C23, is connected between the base of transistor Q8 and ground. The collector output of transistor Q6, appearing across capacitors C21 and C19 as stabilizing capacitors, is connected to the base input of transistor Q4. The collector of transistor Q4 is connected to ground, and a stabilizing capacitor C20 is connected between the emitter and ground, with the result that a restored D.C. voltage is applied to summing junction SJ1, at which point the conventional bias from the VCC and the effect of emitter-collector reaction of transistor Q4 meet, with the result that this voltage plus base currents from transistors Q1 and Q2 across resistors P14 and R22 provide D.C. bias for D.C. restoration circuit 124.
Thus, as one effect of the above, the voltage drop across resistor 25, bypassed to ground by capacitor C15 and applied to the base bias of transistor Q5, determines the amount of current supplied to differential amplifier 110 through resistors R13 and R21. Finally, a VCC terminal is connected through resistor P26 to the emitter of transistor Q5, and the collector of this transistor provides a current limitation characterized type bias through resistors R13 and R21, respectively, to emitters of transistors Q1 and Q2.
As a result of the base bias voltages, derived as stated, to transistors Q1 and Q2 and the emitter biases to transistors Q1 and Q2 as just described, there is effectively created a feedback system which modulates supply current to transistors Q1 and Q2 at a voltage to maintain the collector outputs of transistors Q1 and Q2 within a selected range, as at the output of transistor Q2 and across resistor R36. Accordingly, there is provided an-optimum single-ended video signal for the base of transistor Q7 and an optimum output to monitor 69.
Receiver 74 thus functions to provide a high frequency boost by virtue of the RC circuits 7, 8, 9, 10, and C8 which effects A.C. gain and phase shifts at various frequencies in the frequency region up to 200 MHZ and thus to achieve a final frequency compensated signal response to monitor 69.
Referring back to
Green and red receivers 76 and 78 are illustrated only in block form and function as receiver 74, as described above. The outputs of the receivers are provided to monitor 69, being a green signal as the output of receiver 76 and as a red signal of the output of receiver 78. With the frequency compensation and delay adjustments described above, there is provided to monitor 69 a coordinate signal wherein the interconnections and timings of the color signals are such as to provide a composite signal with excellent color quality despite the most unlikely medium of cable transmission. Again, the adjustments are simply to adjust the filter insertions and delay insertions, as described above, to effect optimum quality.
Most significantly, this invention provides a means of color communications in literally thousands of locations having twisted pair installations at low cost which otherwise could cost the users quite large sums as required to replace twisted pair telephone lines with conventional high frequency conductors.
While the invention has been particularly shown and described with reference to embodiments thereof, those skilled in the art will understand that the foregoing and other changes in form and detail may be made therein without departing from the spirit and scope of the present invention.