GB1268649A - Voltage-to-frequency conversion apparatus - Google Patents

Abstract

1,268,649. Automatic frequency control; pulse modulation circuits. HONEYWELL Inc. 21 Feb., 1969 [1 March, 1968], No. 9491/69. Headings H3A and H4L. [Also in Division G4] A circuit for providing an output whose frequency is proportional to the amplitude of the input comprises an operational amplifier 13 feeding a voltage-to-frequency converter 14, a degenerative feedback signal being fed from the converter to the input of the amplifier. The amplifier 13 (not described in detail) is of the kind which maintains the feedback current I 2 equal to the input current I 1 whereby, since I 2 is proportional to the output frequency of the converter, the frequency is proportional to the input signal. Input signal I 1 and feedback signal I 2 are fed to a common junction and thence to one terminal of the amplifier 13. The output of the amplifier controls the conduction of transistor 53 which determines the rate of charge of capacitor 64. As the capacitor charges, the voltage on the cathode of SCR 63 falls until it reaches the bias voltage supplied by potentiometer 57-60, whereupon the SCR fires, discharges the capacitor and returns to non- conductive condition. A voltage developed across resistor 62 by firing of the SCR causes output transistor 67 to conduct. The output, in the form of voltage spikes, is fed to a flip-flop 70 having outputs A 1 , B 1 which are alternately energized. The outputs are coupled via circuits 47, 39, 37 and 48, 40, 38 to the bases of transistors 30, 31 which are alternately rendered conductive, and regulate the charge and discharge of a precision capacitor 34. The capacitor is charged from a source of constant voltage E R so that discharge current I 2 (smoothed by capacitor 33) is proportional to the frequency of the flip-flop and hence of the converter 14. Transistor 56 provides a low limit bias to the capacitor 64, i.e. it supplies current to the capacitor when the output of amplifier 13 falls sufficiently to cause transistor 53 to approach cut-off. When the amplifier output reaches a certain minimum value, transistor 68 becomes conductive and terminates operations by grounding the outputs of the flip-flop 70. An output circuit 16 (Fig. 4, not shown) consists of a second flip-flop driven by the flip-flop 70 and, in turn, driving the winding of a motor through a pair of alternately conducting transistors. The motor moves through one increment as each transistor conducts and thus performs an integration. An alltransistor version of the converter 14 is described with reference to Fig. 4 (not shown).