GB592372A - Improvements in or relating to time-base generators incorporating thermionic amplifiers - Google Patents

Abstract

592,372. Saw-tooth waveform generators. MACKAY, D. M., and WRIGHT, C. S. May 5,1945, No. 11510. [Class 40 (v)] A time base waveform with an expanded or contracted portion is generated by a thermionic amplifier with a capacitive feedback path between the output and input electrodes, the amount of 'feedback being changed during the time base sweep by adding or subtracting further capacitive elements by means of an electronic switch. In Fig. 1, network R1, C1 is the additional circuit element connected in parallel with condenser C in a "Miller" integrating circuit. Diode D is non-conducting at the incidence of the positive square wave at the suppressor grid of valve A, and R1, C1 is effective with condenser C in determining the rate of fall of anode voltage Va down to the level V1. Diode D then conducts and clamps the junction of R1 and C1 at the voltage V1, so that the network is ineffective for the rest of the discharge path which is consequently steeper than before. Alternatively, a second diode may replace resistor R1 which is then connected between the junction of the two cathode leads and the negative H.T. terminal. The initial discharge may be given the greater slope by reversing the diode connections, and returning resistor R1 to the positive H.T. terminal in the case of the double-diode arrangement. Fig. 6 shows a modification which produces a contracted portion within the operating range of anode voltage Va. When Va is greater than VI or less than V2, diode D1 or D2 is conducting and an additional circuit R1, C1 or R2, C2 is effective in the discharge circuit. When Va lies between V1 and V2, however, both diodes are conducting and the discharge proceeds at a higher rate since both networks are now ineffective. An expanded portion may be obtained between voltages V1 and V2 by connecting the anode and cathode of diodes D1 and D2 respectively to a single network R1, C1.