US 3458723 A
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July 29, 1969 F. L. HANSON SQUARE WAVE GENERATOR Filed Sept. 9, 1966 0,0. SUPPLY +v HLE i 19 t 13 ourpur SOURCE D.C. SUPPLY INVENTOR ATTORNEY United States Patent 'Ofli ce 3,458,723 Patented July 29, 1969 3,458,723 SQUARE WAVE GENERATOR Fred L. Hanson, Loveland, (3010., assignor to Hewlett- Packard Company, Palo Alto, Calif., a corporation of California Filed Sept. 9, 1966, Ser. No. 578,276 Int. Cl. H03k 17 /6'0 US. Cl. 307-240 4 Claims This invention relates to a square wave generator and has as its principal object the provision of a circuit for producing a square wave signal of accurately known true RMS value. This is accomplished according to the illustrated embodiment of the present invention by switching alternately between regulated power supplies of equal amplitude and opposite polarity.
Other and incidental objects of the present invention will be apparent from a reading of this specification and an inspection of the accompanying drawing which shows a schematic diagram of the circuit of the present invention.
Referring to the drawing, positive and negative DC supplies 9 and 11 are shown connected to a common output terminal 13, respectively, through serially-connected regulators and transistor switches 15, 17 and 19, 21. A transistor switch 23 parallels the switch 17 in the positive channel and transistor switch 25 parallels the switch 21 in the negative channel and all four switches 17, 21, 23 and 25 receive the switching signal from switching driver source 27 on their respective base electrodes. Regulator controlling amplifiers 29, 31 are connected to receive the combination of a reference voltage and a voltage proportional to the voltage at the output of the regulator for applying a control signal to the respective regulator for maintaining the regulator output substantially constant. The transistor switches 17 and 21 are chosen to be complementary conductivity types and the switches 23 and 25 are chosen to be of the conductivity type which is complementary to the conductivity types of the switches they parallel. Thus, for a driving signal of alternating polarity and selected frequency from switching driver 27, one of the DC supplies 9, 11 is connected to the output 13 through its respective regulator and switch while the other DC supply is disconnected during one half cycle of the driving signal from source 27 and then said other supply is connected to the output terminal 13 through its respective regulator and switch while said one supply is disconnected.
In the improved square wave generator of the present invention, the regulators in each of the positive and negative channels are continuously operable within their respective feedback paths despite the alternate connection of the channels to the output terminal. Assuming switch 17 is conducting on a half cycle of one polarity from source 27, then amplifier 29 receives the combination of a reference voltage and the output terminal voltage divided down by the combination of resistors 33 and 35. The conductive ones of switches 17, 21, 23 and 25 are thus within the feedback loops and changes in their conductances during the time they are heavily conductive do not materially alter the output terminal voltage. At the same time, amplifier 31 receives the combination of the reference voltage and the voltage at the output of the regulator divided down by the combination of resistors 37, 41 and 39 for controlling the regulator 19 to maintain its output voltage substantially constant during the time it is disconnectedby switch 21 from the output terminal 13.
Duringthe alternate half cycle of operation, the output terminal voltage is divided down by the resistors 39 and 41 and compared in amplifier 31 with the reference voltage for controlling regulator 19 now connected to output terminal 13 through switch 21. At the same time, the voltage at the output of regulator 15 is divided down by resistors 35, 33 and 43 for comparison with the reference voltage in amplifier 29 which, in turn, controls the regulator 15 to maintain its output constant. Thus, compared with the conventional technique of switching the regulators on and off the regulators 15 and 19 of the present invention are virtually unaffected by the alternate connection of their outputs to the output terminal (with the exception of minor regulation necessary to compensate for very small currents drawn from the output terminal in practice). Thus, since the regulators are operating at a DC level which remains fixed typically to within 5 millivolts (to compensate for output current), the channels can be switched at frequencies ranging from DC to frequencies of the order of several megacycles without significantly altering the wave shape or alfecting its amplitude.
I claim: 1. A signal generator having an output and comprising:
a pair of unidirectional voltage supplies of opposite polarity; a signal-controlled regulator serially connected to each of said supplies; first switching means connected to each of the regulators for selectively connecting a regulator to the output of the generator; a first voltage divider and an amplifier for each of said regulators; means including the first voltage divider connected to the output of the generator and including the amplifier connected between the divider and the respective regulator for applying a control signal to such regulator for maintaining the voltage at the output of the generator substantially constant during the time said first switching means connects such regulator to the output of the generator; and second switching means and a second voltage divider for each of said regulators, the second voltage divider and second switching means being serially connected between the respective regulator and the amplifier therefor for controlling such regulator to maintain its output substantially constant during the time the other regulator is connected to the output of the generator. 2. A signal generator as in claim 1 wherein: the first and second switching means include transistors and a source of switching signal connected to the bases of said transistors, and the transistors in the first switching means are of complementary conductivity type and the transistors in the second means connected to a regulator are of conductivity types opposite to the conductivity type of the transistor in the first switching means connected to such regulator. 3. A signal generator as in claim 1 wherein:
3 4 the first voltage divider for each regulator includes first same regulator are alternatively and cyclically rendered and second resistors serially connected in that order conductive and nonconductive in opposite phase relationbetween the output of the generator and a source of ship.
reference potential with the common connection of the resistors connected to said amplifier for such reg- 5 References C'ted hulator; and v UNITED STATES PATENTS t e second voltage divider for each of said regulator includes a third resistor and both resistors of the first 3359433 12/1967 Thauland 307 243 voltage divider for such regulator with the common ROY LAKE, Primary Examiner connection of the third and second resistors con- 10 nected to the amplifier for such regulator. JAMES MULLINS Asslstant Exammer 4. A signal generator as in claim 2 wherein the transistors in the first switching means and also the transistors in the first and second switching means connected to the 307-243, 260,