Patent GB-801593-A (GB)
Title: Improvements in or relating to electronic circuits
Inventor: PERRY GERALD HORACE
IPC: H03K5/00
Filed: 1955-06-23
Abstract: 801,593. Staircase and sweep-voltage generators. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Sept. 21, 1956 [June 23, 1955], No. 18242/55. Class 40 (6). A step waveform generator comprises a capacitor to one plate of which a voltage generator is connected, the other plate being connected to a circuit which clamps the voltage of the plate to a datum value. The generator and clamping circuit are controlled so that the voltage from the generator may be varied and the operation of the clamping circuit may be inhibited. When the voltage on the second plate has reached a given value the variation is stopped and the clamping circuit re-operated so that a voltage step is generated on one plate of the condenser, the height of the step being determined by the difference between the value of the datum and the voltage which the plate of the condenser has attained. Fig. 2 shows a self-running staircase waveform generator in which a linear Miller sweep circuit 1 controls the voltage of the left-hand plate of capacitor C, the right-hand plate being connected to a clamping circuit comprising diodes D1 and D3, the clamp circuit being itself controlled by a bistable circuit 4, the voltage level which the right-hand plate attains being detected by a circuit comprising diodes D12, D13. If it is assumed at the commencement of operation that the cathode of diode D3 has been taken negative by the output 4a of bistable circuit 4 so that the diodes D1 and D3 conduct then the anode of diode D1 is earthed and the right-hand plate of capacitor C is clamped at earth potential. If the cathode of diode D3 is taken positive by output 4a diodes D1 and D3 are non-conducting diode D13 is conducting and D12 cut off so that the righthand plate of capacitor C is open-circuited. If current flows into the virtual earth input 1a of generator 1 via diode D5 the output of generator 1 and the right-hand plate of capacitor C rise to a voltage 10 volts when diode D3 conducts and diode D13 is cut off. A current proportional to this rate of rise is fed via capacitor C1 into bistable circuit 4 causing it to trigger to its second stable state. When this occurs the anode of diode D6 goes positive and diode D5 is cut off so that further rise of the voltage at the output 1b of generator 1 is prevented, the cathode of diode D3 is taken negative by output 4a, thus clamping the righthand plate of capacitor C to earth and initiating the sweep voltage generator 5 through diode D11. The sweep output from generator 5 rises until diode D5 conducts and cuts off diode D4; this causes the right-hand plate of capacitor C2 to rise and trigger circuit 4 to its original stable state. The output 4a of circuit 4 stops the sweep generator 5 and returns it to its starting point, thus taking the cathode of D3 positive and removing the clamp from the righthand plate of capacitor C. The output 4d lowers the anode voltage of diode D6 allowing current to flow again to the virtual earth input 1a of generator 1 so that its output voltage starts to rise to form another step and the cycle is repeated. When the voltage of output 1b of generator 1 causes diode D2 to conduct the monostable circuit 7 is triggered to its unstable state in which it remains for a predetermined time. Whilst in this state the anode of D4 is taken positive thus feeding a current of opposite sign into the input 1a of generator 1 and causing its output voltage at 1b to return to its starting point. On transition of circuit 7 from the unstable to stable state the output is differentiated in circuit D7a, D7b and fed through diode D7 to reset bistable stable 4, thus enabling the complete set of step cycles to be repeated. In addition to the staircase waveform generated at the output of generator 1 as shown in Fig. 3, a sweep voltage is generated by unit 5, each sweep of which is effectively synchronized to the timing of the steps in the staircase waveform. Additional accuracy of step height determination may be obtained by controlling the bias level on the anode of diode D1 from the anode of an additional diode connected in series with the bias source and the resistor so that any contact potential variation of one will be counter-balanced by the other.