Patent GB-587610-A (GB)
Title: Improvements in or relating to electric thermionic valve integrating arrangements
IPC: H03K4/86
Filed: 1944-12-01
Abstract: 587,610. Saw-tooth generating circuits; code telegraphy. STANDARD TELEPHONES & CABLES, Ltd.. and JACOBSEN, B. B. Dec. 1, 1944. No. 24042. [Classes 40 (iii) and 40 (v)] In an integrating circuit, in which a current charges or discharges a condenser connected between the output and input of a D.C. amplifier so that the voltage developed in the output circuit acts in opposition to that acquired by the condenser, the amplifier comprises an oscillation generator, the oscillations being rectified to produce the D.C. output, the difference between the voltages being used to vary the amplitude of the oscillations. The valve 9, Fig. 2, connected to oscillate at a frequency determined by the primary of transformer 10 and condenser 12, produces D.C. potentials across resistances 5, 20 due to the rectification of the output by voltage doubler network 18, 19, 21, 22. When a positive potential is to be integrated, the cathode bias combination 11 is adjusted to prevent valve 9 from oscillating, terminal 7 being at earth potential since there is no output from valve 9. The grid is momentarily earthed through switch 27, the applied potential then causing condenser 4 to charge over resistance 3, the resulting rise in grid potential causing a corresponding steady increase in the amplitude of the oscillations generated and a negative D.C. potential to appear across resistance 5. For a limited range, the amplitude of the oscillations increases linearly with increase in grid potential. The rise in potential across condenser 4 is largely offset by the almost equal and opposite change across resistance 5, so that the flow of current in resistance 3 is affected to only a minor extent. The potential across resistance 5 may be measured by a suitable instrument to give the integrated output. An equal and opposite potential across resistance 20 may be utilized, condenser 22 and resistance 20 being omitted when this output is not required. To integrate a negative potential, the bias is adjusted for maximum amplitude of oscillation of valve 9 consistent with linear control by grid potential, the grid being earthed momentarily through switch 27 and switch 23 operated so that the negative potential developed across resistance 5 may be opposed by suitable adjustment of potentiometer 24. Switch 27 is opened and condenser 4 charges negatively to increase the negative bias on the grid of valve 9 and decrease the amplitude of the oscillations, the negative potential across resistance 5 falling with the result that the potential rises with respect to earth towards the setting of potentiometer 24. The valve 9 may be a tetrode, the secondary of transformer 10 being connected to the second grid. By inserting a diode in series with the input, only currents of one sign are integrated, and by using two diodes with opposite connections to two integrating circuits, separate results may be obtained. To generate a linear time base, Fig. 5 (not shown), a gas-filled diode or triode may be connected across condenser 4 or resistance 5, firing when the potential reaches the critical value, to discharge the condenser.. The gasfilled triode may be triggered by a signal applied to the grid over a limiting resistance or to the cathode over a transformer shunted by a rectifier. The circuit may be used for frequency dividing by suitable choice of the synchronizing pulse amplitude. Where a singlestroke time base is required, the gas-filled valve is so biassed that the potential across condenser 4 does not rise to the firing potential of the valve, a pulse on the control grid or cathode initiating the discharge. When condenser 4 is arranged to charge negatively, the gas-filled triode is inverted. Alternatively, a triggering pulse may be applied to an auxiliary grid in valve 9 to increase momentarily the amplitude of the oscillations and so fire the gas-filled valve. In a modification, a negative pulse, applied to an additional grid in valve 9, stops the oscillations, condenser 4 discharging through grid-cathode path of valve 9. To avoid an A.C. potential appearing across the input, the condenser 4, Fig. 7, may be isolated from the grid of valve 9 by a stopper resistance 45. To reduce the effect of the gridearth potential tending to discharge condenser 4 through the external circuit, the potential to be integrated is applied to condenser 4 and through a bias source to the cathode of a cathode follower valve 48, any increase in D.C. potential due to condenser 4 charging resulting in an almost equal change in the cathode potential of valve 48. In a further modification, Fig. 9 (not shown), a potentiometer is connected between the input terminal and resistance 20, the resistance 3 being connected to the slider, an equal potential being applied to condenser 4 to prevent its discharging. In a circuit of the type shown in Fig. 2, a separate rectifier circuit may be used for this purpose. The natural .leakage of condenser 4 may be neutralized by a compensating arrangement, Fig. 8 (not shown), in which a resistance is connected between the junction of resistance 3 and condenser 4 and resistance 20. By decreasing the compensating resistance, the leakage through the external circuit may also be compensated. As applied to a low-frequency signalling circuit, Fig. 10, a square wave fed over submarine cable 55 appears distorted at the secondary of transformer 54. A potentiometer 58 allows a potential to be tapped off consisting of the received signal mixed with a variable amount of the' integrated signal. The resulting potential more nearly approximates to the transmitted signal. Specifications 545,866 and 575,250 are referred to.