GB941731A - Improvements in electrical circuits having non-linear transfer characteristics - Google Patents

Abstract

941, 731. Electric analogue reaction generators. BRITISH BROADCASTING CORPORATION. June 17,1960 [April 3, 1959], No. 11473/59. Heading G4G. A non-linear circuit for television signals comprises two valves having substantially identical characteristics and cathode loads; a black level clamping circuit connected in the input to the control grid of the first valve; means for biasing the second valve such that the two cathode potentials are the same when the control grid of the first valve is clamped; and a non-linear output circuit connected between the first and second cathodes which includes two series connected resistors, the second of which is shunted by at least one further resistor over a predetermined range of signal levels. The input signal fed to valve VIA is clamped by clamp circuit 12 to the potential determined by the position of the slider on potentiometer RV1, the potentiometer being adjusted to give equal cathode potentials on valves V1A, V1B when the grid of VIA is clamped. The potential at the point E thus corresponds to black level. A third valve V2B has its grid biased to a higher potential than that of V1B, such that the potential Eg at its cathode corresponds to peak white signal, and potentials corresponding to any signal level may be tapped off from RK3. These tapping points are connected to series arrangements of resistors and diodes D1, R3 and D2, R4 which are arranged to shunt a part R2 of the load connected between cathodes, to produce the required non-linear characteristic. The output is fed to a paraphase amplifier V3, V4. A further valve V2A has its cathode connected directly to that of V1A, and has its grid fed with suppression pulses during the line suppression period, the arrangement being such that at other times it is cut off. The pulses appear in the output and may be used as a reference when setting the gain of the amplifier. The non-linear circuit is made as a plug-in unit for ease in changing the characteristic.