GB682864A - Improvements relating to circuits for generating sawtooth waveforms - Google Patents

Abstract

682,864. Saw-tooth generating circuits. ELECTRIC & MUSICAL INDUSTRIES, Ltd. May 24, 1950 [June 21, 1949], No. 16413/49. Class 40 (vi). In a saw-tooth waveform generator of the type in which a capacitor is charged via a resistor from a constant voltage source and periodically rapidly discharged, the linearity of the long flank of the saw-tooth waveform is improved by providing in series with the capacitor and resistor a low impedance voltage source of substantially parabolic waveform. Fig. 1 shows a saw-tooth generator in which capacitor 1 is charged from a source 3 via a resistor 2 and periodically discharged via valve 4 when this valve is rendered conducting by positive-going pulses applied from source 5. The saw-tooth voltage produced across the capacitor which has an exponential curvature to its long flank is integrated by network 8, 9 to produce a low impedance voltage source of voltage (a) across cathode resistor 11. This voltage is thus effectively in series with the voltage across capacitor 1 and thus produces a linear flank to the saw-tooth waveform produced at terminal 13. Fig. 2 shows a modification in which the saw-tooth voltage produced across capacitor 1 is amplified in cathode follower 10 and the voltage produced across resistor 11 is integrated in network 14, 15 so that the parabolic voltage produced across capacitor 14 is effectively in series with the charging voltage source to capacitor 1 and a linear saw-tooth voltage is thus produced. Third order correction may be produced by feeding a voltage to capacitor 1 from the anode of valve 10 via resistor 17.