Patent GB-1261657-A (GB)
Title: Pulse frequency modifying circuit
Inventor: MOLNAR KALMAN
IPC: H03K7/06
Filed: 1970-05-15
Abstract: 1,261,657. Pulse modulation circuits. MERESTECHNIKAI KOZPONTI KUTATO LABOEATORIUM. 15 May, 1970 [15 May, 1969], No. 23786/70. Heading H4L. In a circuit for modifying the pulse rate in a pulse train in accordance with a predetermined law (e.g. for correcting for non-linearity in a pulse-frequency modulator) first means responsive to the pulse train generates a corresponding series of pulses in which each pulse is of predetermined amplitude and duration, second means responsive to the mark/space ratio of said series produces a signal having an amplitude which is a predetermined function of the mark/space rates and converts said signal to a further series of pulses having a repetition rate dependent upon the amplitude of said signal and third means combines the input signal. and said further series of pulses to produce a. pulse train modified according to said predetermined law. As drawn'in Fig. 8, the input pulses, Fig. 1, are supplied via terminal 1 to a monostable device 8, and the resulting pulses of constant amplitude U2 and duration To, Fig. 2, are passed via a D.C. blocking capacitor 9 and resistor 10 to a circuit 17, which is arranged to provide the required modification. Due to the circuit 9, 10, the input, Fig. 3, to circuit 17 consists of pulses having a positive amplitude U3 which is proportional to the repetition frequency of the input pulses, the zero level being shifted-inaccordance with the mark/space ratio of the pulses U2. The circuit 17 includes a number of elements 15 which in conjunction with a reference, voltage - U R  build up the required characteristic by approximate straight line sections, the outputs of the elements being summed in operational amplifier 16. The output of circuit 17, of the formshown in Fig. 4, for example, assuming that the linearity error is negative; consists, of negative pulses - U 4  whose amplitude is proportional to the error, and these pulses are supplied, via switch 18, controlled, by monostable 8 to a clamping and inverting circuit 22 which produces the variable amplitude pulse train U 5 , Fig. 5. Pulses U 5  aresupplied: to a voltage-to-frequency, converter 39 comprising an integrator 27 and pulse generator 38. The output of the integrator rises in a negative or positive sense, depending on the direction of the error, until a predetermined negative or positive level is reached and a gate 28 or 29 is opened and supplies a pulse from monostable 8 to operate a bi-stable 34 or 35, the bi-stables being reset by the output of an inverter 32. Bi-stables 34, 35 control switches 36, 37 respectively. Switch 36 applies a reference voltage - UR of opposite polarity to that of the 'input signal to the input of the integrator 27 which discharges the capacitor 26 by a predetermined amount and the operation then is -repeated. Switch 37 similarly connects a vol- .tage U R  to the input of the integrator. Thus when the non-linearity is in a negative sense, pulses U 6 , Fig. 6, at a rate proportional to the error, appear at output terminal 6 and-are added at 44 to the input signal from terminal 1 to produce pulses U 7 , Fig. 7. The -addition is carried out by a monostable device 43 which is triggered by the pulses from 1 and 6 the resulting pulses U 7  being passed by a gate 48 to the - output 7. The first pulse U, operates a bi-stable 46 to enable the gate 48. If the error is in a positive sense the correcting pulses appear at output 40 and are supplied to a pulse subtracting circuit 50 to change over the bi-stable 46 to block the gate 48 and prevent the transmission of the next pulse from monostable 43. However this pulse, via delay 49 and bi-stable 46 enables the gate 48 for the following pulses until the next pulse appears on output 40 and the operation is repeated. In a modification, Fig. 9 (not shown), the switch 18 is dispensed with and a diode is inserted between circuits 11 and 17. In a further modification the monostable 8 controls the application of-the reference voltage - U R  to the circuit 17.