GB1206934A - Improvements in or relating to analogue voltage storage apparatus - Google Patents

Abstract

1,206,934. Analogue storage circuit. MINISTER OF TECHNOLOGY. 31 Oct., 1967 [2 Nov., 1966], No. 49091/66. Heading H3T. An analogue voltage is stored on a capacitor by writing pulses from a low-impedance source applied through a transistor connected to the input and the capacitor via respective unilaterally conducting devices, and is read out by means of pulses from a high-impedance source connected to the capacitor and to an output circuit via respective further unilaterally conductive devices. In Fig. 2 an analogue voltage at V in is transferred to the capacitor C1 by an enabling pulse on transistor Q4 which turns on Q3 and allows diodes D1 and D2 to conduct. The duration of the enabling pulse should be very much greater than the time-constant C1R1, and the latter should be less than the period of any variations in V in . To read out, a positive pulse is applied to the top of R2 so that diodes D3 and D4 and transistor Q2 are turned on and the voltage on C1 is transferred to V out . The duration of the read-out pulse should be much less than the time-constant of C1R2 (so that the read-out will be non-destructive), but longer than COR2 where CO is the stray capacitance between the base of Q2 and earth. This capacitance is discharged through diodes D6 and D7 and transistor Q6 by turning on the latter immediately before read out. The above circuit may be arranged in multiple to form a matrix, with transistor Q1 and resistor R3 common to all the circuits. Those in one row may be activated in succession by applying a long enabling pulse to transistor Q5 and a succession of shorter pulses to Q4, thus sampling V in at different instants in time. The bases of Q4 and Q5 in several rows may each be connected to a single stage of two separate ring counters (not shown), one selecting a row and the other a particular circuit in a row. Transistor Q2 may similarly be common to a row of circuits, read-out being enabled by a long positive pulse on the collector of Q2. This and R2 may be connected to ring counters as for Q4 and Q5. To maintain the voltage on C1 for a long time, the read-out voltage may be applied to a voltmeter having an output connected to a digital-to-analogue converter and the next highest voltage step impressed on C1. Transistors of opposite conductivity types may be used, with reversal of polarities of the diodes and supplies. Q2 may be a cathode-follower valve. The arrangement may be used to store information obtained during the ultrasonic testing of metallic objects.