GB786643A - Improvements in or relating to electric signal generators - Google Patents

Abstract

786,643. Sawtooth generator circuits. CINEMA-TELEVISION, Ltd. Nov. 16, 1955 [Nov. 16, 1954], No. 33155/54. Class 40 (6). A signal generator for producing a sawtooth waveform balanced about a mean potential in response to a control pulse comprises a first pulse generator which generates an output pulse of predetermined duration in response to the control signal and a second pulse generator triggered by the cessation of the pulse generated by the first pulse generator to produce a second pulse of predetermined duration, thus in response to pulses from the first generator the charge in a capacitor is altered at one rate and a second generator prevents the charge in the capacitor from being altered in the same sense at another rate, the charge in the capacitor being changed in the opposite sense continuously. Fig. 3 shows a sawtooth generator in which the flip-flop circuit comprising cathodecoupled valves 11, 12 is triggered by a negative pulse applied at input 10 to generate a negative output pulse of predetermined duration at the anode of tube 12. This pulse is applied to the control grid of tube 18 to cut it off, so that its cathode goes negative until it reaches a voltage lower than that at which capacitor 42 is clamped by tube 21, diode 20 thus conducts and the portion AB of the waveform shown in Fig. 2 is generated. When the pulse on the grid of tube 18 ends diode 20 is cut off. The positive-going voltage at the anode of tube 12 triggers a second cathode-coupled flip-flop circuit comprising tubes 14, 15 to generate a positive pulse at the anode of tube 15 this causes tube 17 to conduct, its cathode going positive so that diode 19 is cut off. The potential on capacitor 42 rises due to current flowing into it through resistors 43, 44, thus generating the main stroke BC of the sawtooth waveform shown in Fig. 2. At the end of the second pulse valve 17 is cut off so that diode 19 passes current and capacitor 42 discharges until diode 21 conducts and clamps the voltage across capacitor 42, thus generating portion CD of the waveform shown in Fig. 2. The potential across capacitor 42 is applied to the grid of tube 22 which is connected in a " boot-strap " circuit, the voltage at its cathode being applied back to charging resistor 43 so that the charging rate remains constant. Non- linearity of the discharge is reduced by returning discharging resistors 40 and 45 to the junction of suitably chosen resistors 48, 49 in the cathode of tube 22. The circuit may be modified, Fig. 5, not shown, to generate the inverse sawtooth waveform as shown in Fig. 4.