GB1086533A - Improvements in or relating to non-linear amplifier arrangements - Google Patents

Abstract

1,086,533. Electric analogue calculating. MARCONI CO. Ltd. Nov. 25, 1964 [Feb. 19, 1964], No. 6918/64. Heading G4G. A circuit for approximating to a desired non- linear input/output transfer characteristic e.g. for television gamma correction comprises a transistor VT1 whose base receives an input signal and whose emitter output is coupled over resistors R2 and R5 respectively to the bases of transistors VT3, VT4 whose emitter circuits energize opposite ends of potentiometer RV2 whose slider is connected to the base of output transistor VT5 energizing the output. Transistor VT2 operates as a low impedance reference voltage source whose base is connected to a slider of a potentiometer RV1 across the operating power supply, and whose emitter is earthed over series resistors R9, R10, R4 and is connected over R3 and R2 to the emitter of VT1 to which the junction of R4, R10 is also connected over R8 and R5. Potentiometer RV1 is adjustable so that the emitter voltages of VT1, VT2 are equalized. The junction of R5, R8 is connected to the emitter of VT2 over diode MR2 and resistor R6, and to the junction of R9, R10 over the diode R1 and resistor R7 in a non-linear network such that lower levels of the input signal provide a relatively greater proportion of the output signal than do higher levels; the overall transfer characteristic approximating to an inverse square law. R2, R3 are chosen so that at maximum input signal the outputs of transistors VT3, VT4 are equal and adjustment of RV2 varies the proportions of such outputs applied to the base of VT5 to energize the circuit output. The input may be a linear sawtooth signal, and the waveform of the output is variable with the position of the potentiometer slider (Fig. 2, not shown).