GB660675A - Improvements in frequency-dividing circuits - Google Patents

Abstract

660,675. Pulse generating circuits. MURPHY RADIO, Ltd., DAVIES, S. N., and HUMPHREY, K. G. Feb. 10, 1950 [Feb. 10, 1949], No. 3690/49. Class 40 (vi). The synchronizing pulses for a multivibrator are applied across a resistor which is connected in parallel with a cathode resistor in each valve of the multivibrator through a rectifier which conducts when the associated valve is passing current. The Figure shows a multivibrator used as a frequency divider, in which the positive-going pulses which are to be divided are applied across resistor 7. Diodes 8 conduct only when the associated valve is passing current when the synchronizing pulses appear across the anode load and are thus applied to the grid circuit of the other valve which is non-conducting at that instant. Both change-over points of the multivibrator are thus triggered, and the division ratio is unaffected by small drifts in the frequency of the incoming pulses. The diodes 8 only conduct when the amplitude of the input pulses is equal to or less than the value of cathode bias of the associated valve. The stability of the circuit is thus less affected by changes in amplitude of the input pulses or by changes in the H.T. supply or in the valve characteristic. If, for example, the H.T. supply voltage increases the reduction in frequency of the multivibrator which would normally occur is offset by the increased amplitude of synchronizing signal which is applied to each valve as a result of the increase in cathode bias voltage.