Patent GB-1001815-A (GB)
Title: Wave generating circuits
IPC: H03K3/315
Filed: 1962-04-03
Abstract: 1,001,815. Trigger circuits employing tunnel diodes and transistors; automatic phase-control systems. RADIO CORPORATION OF AMERICA. April 3, 1962 [April 19, 1961; April 20, 1961], No. 12804/62. Headings H3A and H3T. A semi-conductor switching circuit comprises a transistor supplied with operating potentials, a tunnel diode connected between the emitter and base electrodes of the transistor and poled so as to have the same forward direction of conduction as the emitter-base diode of the transistor, and a feed-back connection 20 made between the emitter-collector path of the transistor and the tunnel diode that when the tunnel diode switches from its low-voltage to its highvoltage state or vice-versa, the consequent increase or decrease in conduction in the transistor tends to restore the tunnel diode to its original state. The circuit may be adapted to be either bi-stable, mono-stable, or astable. In a first circuit comprising a free-running sawtooth generator, Fig. 1, charging of capacitor 28 continues until sufficient current passes through feed-back resistor 21 to switch the tunnel diode 17 to its high-voltage state. The voltage then established across the tunnel diode is sufficient to render transistor 10 fully conducting so as to discharge capacitor 28, the discharge continuing until the tunnel diode is switched back to its low-voltage state and the transistor rendered non-conducting. As a result the circuit oscillates continuously, a sawtooth waveform being developed across capacitor 28. The frequency of oscillation may be varied by varying the voltage applied at terminal 22. As shown, the frequency of oscillation may be controlled by a phase detector 32 so as to be maintained in synchronism with a standard which may, for example, be a television synchronizing signal. In a second circuit, Fig. 4 (not shown), which may be biased to function either as an oscillator or as a monostable circuit, a rectangular output waveform is developed at the collector of transistor 10. On switching the circuit on, the negative step occurring at the collector electrode is transmitted through the delay means 26 so that provided the positive bias + V, does not exceed a predetermined value, the tunnel diode 17 is switched to its high-voltage state and the transistor is rendered conductive. The consequent positive step at the collector of transistor 10 then passes through the delay means so as to restore the tunnel diode to its low-voltage state and to switch the transistor off. This switching occurs at a regular rate and a rectangular waveform appears across output terminals 25. The delay circuit may take the form of a resistance capacitance ladder network, Fig. 8 (not shown), or of an inductor and resistor connected in series, Fig. 9 (not shown). Increase in the positive bias +V, reduces the frequency of oscillation; increase beyond a certain point prevents sufficient feed-back ever being applied to switch the tunnel diode to its high voltage state. In this case application of a short negative pulse at input terminals 22 will switch the diode to its high voltage state until the voltage fed back through the delay means switches it off again, i.e. the circuit is now monostable. Alternatively, by the application of a suitable long negative pulse at terminals 22, the circuit may be made to function as a gated oscillator. In a further form of the circuit, Fig. 12 (not shown), feed-back is effected from the emitter circuit of the transistor. The circuit may be either monostable or free-running. Considering its operation as a free-running circuit in which regular rectangular pulses are produced at the collector of transistor 60. When the transistor is switched off, capacitor 78 charges towards the positive voltage +V 3  until the potential at the emitter becomes sufficient to cause the tunnel diode 62 to assume its high voltage state whereupon the transistor is switched on. The capacitor then discharges and the potential at the emitter' falls until this potential becomes so reduced that the tunnel diode reverts to its lowvoltage state and the transistor is switched off once more. The circuit can alternatively be made to function in a monostable fashion or as a gated oscillator by a suitable choice of operating conditions. In a modified circuit, Fig. 11 (not (shown), the capacitor 78 is omitted. This circuit may be made to operate in bi-stable 'fashion and is described as an emitter follower serving for the translation of pulse logic signals and supplying both current and voltage gain at each stage. This circuit may be rendered monostable by connecting an inductor between 'the source - V 1  and the base of transistor 60.