Patent GB-1054400-A (GB)
IPC: H03M1/00
Abstract: 1,054,400. Transistor bi-stable circuits. C. A. PARSONS & CO. Ltd. Nov. 12, 1963 [Dec. 13, 1962], No. 47159/62. Heading H3T. [Also in Division G4] A binary scale counter comprises a number of serial connected bi-stable stages, each characterized in that it is operable to change from one state to the other by the application of pulses derived from the leading or lagging edges of a square wave signal, according to the desired direction of counting. The counter forms part of a digital voltmeter of the kind in which an unknown voltage is balanced by a voltage derived from the value in the counter, the counter being arranged to count up or down until a, balance is reached. The counter is driven by a source of alternating voltage (a), Fig. 4 (not shown), on terminals 1, 2 of a transformer, the output is rectified and shaped by diode 3 and resistor 4 to give a square wave (g). This wave is applied to capacitor to which differentiates the wave to produce peaks (d) which pass to the base of transistor 8, Fig. 3 (not shown). The square wave also passes to an inverter 9 to obtain wave (c) and this is differentiated and the peaks (e) applied to the base of transistor 12. The transistors form switches, only one of which is in operation at a time, according as to whether the counter is to count up or down, the stage switching in response to a change of input of one direction (0 to 1) or the other (1 to 0) according as to whether the signals (d) or (e) control the switch. The counter stage consists of a bi-stable circuit comprising transistors 13 and 14, only one of which is conducting at a time, the potential of the output terminal 23 having two corresponding values. The stage is switched from one state to the other when the switch 8, 12 is momentarily opened to break the current through the conducting transistor. While the transistor 13 is conducting a condenser 15 is charged. If the switch 8, 12 now opens to break the circuit the transistor 13 cuts-off. The potential at junction 26 goes to - 15À5v, the potential of supply line 39, by conduction through the emitter and base (acting as a diode) of the inverter transistor of the next stage. The potentiometer formed by resistor 21, 22 brings the junction 28 to a more negative potential, line 37 being at - 36v, and line 41 at 0v. During conduction the base of transistor is held at a potential more positive than that derived from the potentiometer 18, 19 because of current flowing through resistor 18 via the emitter and base of transistor 13. This potential is maintained by the charge on capacitor 15 during opening of the switch 8, 12. The base of transistor 14 is at a lower potential so that if the switch 8, 12 now recloses transistor 14 conducts first, preventing transistor 13 conducting. While transistor 14 is conducting the potential of junction 29 remains at approximately - 7v (the potential of supply lead 40) and the charge on capacitor falls. When the switch opens and closes again the base of transistor 13 is at a potential lower than that of transistor 14 and consequently it conducts first. Negative biasing lines 30, 31 are provided, one connected through resistor 7 to the base of transistor 8 and the other through resistor 11 to the base of transistor 12. If a change in the value in the counter is necessary to balance the unknown voltage the bias voltage is removed from one of the leads so that the corresponding transistor 8, 12 ceases to conduct and the other one is switched by the positive pulses in the control signal (d) or (e). When a balance has been achieved both lines 30, 31 have a negative bias. The stage switches at each positive pulse of one or the other pulse train (f) and (g). In the first case therefore the stage switches as the result of a change in the input of 0 to 1, the opposite change having no effect. In the second case the change 1 to 0 switches the stage. The output 23 from the stage is connected in exactly the same manner to control the next stage and so on. A change of state in response to an input change of 0 to 1 gives a descending count and a change in response to an input change of 1 to 0 gives an ascending count. Outputs from each stage control currents in weighted resistors 34, 35 &c. through switching transistors 33.