Patent GB-976627-A (GB)
Title: Switching circuits
IPC: H03K3/315
Filed: 1960-12-20
Abstract: 976,627. Tunnel-diode trigger and oscillatory circuits. INTERNATIONAL BUSINESS MACHINES CORPORATION. Dec. 20, 1960 [Dec. 21, 1959], No. 43685/60. Heading H3T. A tunnel diode 12, Fig. 2A, having a characteristic curve 10, Fig. 2B, is supplied from a constant current source 16 and is connected in parallel with a non-linear impedance device, such as a diode 14, which serves as a load for the tunnel diode and has a load-line, such as loadline 18, which intersects the characteristic curve 10 in its high-voltage positive-resistance region. The non-linear impedance device 14 may comprise a forward-bias diode as shown. A Zener diode or the emitter-base diode of a transistor, as in the embodiment shown in Fig. 3. The application of a positive pulse to the base electrode causes an increase in current through the transistor and hence a reduction in current through the diode whereby the diode is switched to the low-voltage region of its characteristic whence it returns, after the pulse has terminated, in a time dependent upon the value of the induction L. The circuit may be made to serve as a pulse-frequency divider for input pulses whose repetition period is less than the relaxation time of the circuit. Alternatively, if the triggering pulse is of relatively long duration and its amplitude is small so that the load line 18, as displaced by the pulse, intersects the negative-resistance region of the curve 10, the circuit becomes astable and oscillations are generated continuously for the duration of the pulse. In a modification, Fig. 9 (not shown), the amplitude of the current from the source 16 is reduced so that the load line intersects the curve 10 in three places and a bi-stable circuit results: Switching is effected by alternately applying voltage pulses to the base of the transistor and current pulses to the diode anode. In Fig. 7 (not shown), similar results are achieved by connecting a resistor in series with the tunnel diode, switching in this case being by alternate positive and negative pulses applied to the base of the transistor. Fig. 11 shows a plurality of circuits coupled together, the load for the first tunnel diode E 1  being provided by the series connection of ordinary diode D 1 , resistor R 3  and tunnel diode E 2 , and so on. Assuming first that both diodes E 1 , E 2  are in their low-voltage states at a point P, Fig. 12, the current I s  from both the sources 16 being less than the maximum of the lowvoltage peak of the characteristic 14, the application of a positive-current pulse to diode E 1  will switch it to its high voltage state, thus causing diode D 1  to conduct so that a load line as shown in broken lines is provided and the diode establishes itself at point Q T . The current now flowing into diode E 2  through D 1  and R 3  will switch this diode to its high voltage state, thus rendering diode D 1  non-conducting so that both of the diodes E 1 , E 2  finally establish themselves at the point Q. To restore the diodes to the low-voltage state the current therethrough must be reduced below the value I R . Owing to the unidirectional properties of diode D 1 , switching diode E 1  to its highvoltage state switches the diode E 2  but switching diode E 2  by itself will leave the state of diode E 1  unaltered.