GB692543A - Improvements relating to non-linear electrical circuits - Google Patents

Abstract

692,543. Electric analogue calculating systems. ELECTRIC & MUSICAL INDUSTRIES, Ltd. April 5, 1949 [April 21, 1948], No. 10954/48. Class 37. [Also in Group XL (c)] In a circuit of adjustable non-linearity for " gamma " correction in television equipment, following a variable fractional power law, the video signal is fed to an impedance network comprising a linear and a non-linear impedance and means are provided for adjustably weighting the output in favour of one or the other response to obtain the desired law. The output of a cathode follower circuit 1, 6 following the head amplifier of a television camera is fed to the input of the succeeding valve 11 through a circuit comprising a resistor 9, an adjustable portion of which is shunted to earth through a diode or a tetrode valve 20 acting as a non- linear resistor. The output from the circuit is applied to the following circuit 19 through resistor 15 and capacitor 17 which also applies negative feed-back to the grid of valve 11 to reduce the input impedance. Resistance 7 is adjusted conjointly with the tapping on resistor 9 to maintain a constance peak-to-peak output amplitude. The output valve may be dispensed with in which case the output is derived from the junction of resistors 8 and 9 and the other end of resistor 9 is earthed. In an alternative arrangement similar to that described in Specification 536,089, Fig. 2 (not shown), the non-linear resistor is connected across an adjustable portion of the load resistor of a high impedance valve and the output is derived from a potentiometer connected across the whole of the anode load adjusted conjointly with the adjustment of the load resistor tap.