GB584329A - Improvements in or relating to circuits employing electron discharge devices - Google Patents

Abstract

584,329. Pulse generating and frequency dividing circuits. WILLIAMS, F. C. Sept. 1, 1944, No. 16741. [Class 40 (v)] A train of pulses, applied to a valve, cause the anode potential to fall in a series of steps until predetermined number has been received when the anode potential returns to the original value. A condenser is connected between the grid and anode of the valve, means being provided for discharging the condenser to form the steps. The pulses to be counted are applied to the grid of pentode V2 and it is assumed that the grid has been driven beyond cut-off before the cycle commences, the anode potential rising exponentially to the anode supply. The rise in anode potential of valve V2 tends to raise the potential of the grid of pentode V1 over the condenser C1 and diode D3 until diode D2 conducts and holds the grid near the cathode potential of diode D2. Due to the cathode load R5, the cathode potential rises to a value slightly above the control grid, the anode current being cut off due to the bias on the suppressor grid relative to the cathode. The anode potential of valve V1 rises exponentially towards the supply voltage until diode D1 conducts. A positivegoing pulse, applied to the grid of valve V2, causes the screen potential to fall, generating a negative pulse which is differentiated over condenser C3 and resistance R6. The short negative-going pulse causes diode D1 to conduct, the anode potential of -valve V1 falling and due to the feed-back condenser C2 the grid potential falls by the same amount. The fall in grid potential results in a corresponding fall in cathode potential, the suppressor grid bias now allowing the valve V1 to pass anode current. The positive pulse applied to the grid of valve V2 also results in a fall in anode potential, the lower plate of condenser C1 falling in potential until diode D4 conducts and substantially discharges the small condenser C1. When the valve V2 is cut off again by the negative-going pulse on the grid, the anode potential rises and hence that of the lower plate of condenser C1 until diode D3 conducts, the condenser C1 then charging to approximately the supply voltage, charge passing from condenser C2. A diode D5 may be included to reduce the charging time of condenser C1. The tendency of the grid of valve V1 to rise is overcome to a large extent by the feed-back action of condenser C2, resulting in a rapid fall or step in the anode potential. When the control grid of valve V2 next goes positive and the valve conducts, condenser C1 is discharged over diode D4, the negative pulse applied to the cathode of diode D1 being ineffective due to the negative bias on the anode. The following negative-going pulse causes the anode potential of valve V2 to rise, condenser C2 discharging into condenser C1 to produce a further step in the anode potential of valve V1. The process is repeated, each negative-going pulse producing a step in the anode potential of valve V1 until it approaches the cathode potential when the feed-back action of condenser C2 ceases. As the anode potential of valve V2 rises, the control grid and anode 'of valve V1 rise, the increased cathode current resulting in a rise in cathode potential above the suppressor grid bias, the anode current thereby being cut off so that the anode potential rises exponentially until diode D1 conducts. The' negative triggering pulse obtained by differentiating the pulse from the screen grid of valve V2 may be made coincident with the step-producing positive pulse from the anode by the use of a delay network. Separate sets of pulses may be used for triggering and stepproducing, the lower frequency triggering pulses being applied to the anode of valve V1, also triggering a cathode-ray tube time base and feeding through an integrating circuit to the cathode of diode D1. The anode potentials is reduced in steps, the number of steps depending on the anode potential as determined by the .cathode of diode D1. The cathode potential may be made to increase one step every cycle so that the return in the anode potential is delayed by the duration of one step, a timing pulse moving discontinuously across the cathode-ray screen. In further modifications, the resistance R1 may be replaced by a shortcircuited delay network, and the diode D4 by a resistance. Specification 582,758 is referred to.