GB1111646A - Improvements in or relating to amplitude modulating circuit arrangements - Google Patents

Abstract

1,111,646. Amplitude modulating systems; pulse modulation systems. TELEFUNKEN PATENTVERWERTUNGS G.m.b.H. 29 Oct., 1965 [29 Oct., 1964], No. 45979/65. Headings H3R and H4L. [Also in Division H2] An inverter circuit comprising a first pair of transistors S1 and S2 of opposite conductivity types and a second similar pair S3 and S4 arranged in a bridge circuit with a D.C. source U connected across one diagonal and an output circuit RLC series resonant at the switching frequency connected across the other diagonal either directly, Fig. 1, or through a transformer (Tr, Fig. 2, not shown), protective diodes G1-G4 being connected across each transistor, is used to provide an amplitude modulated sine wave output in response to relatively phase-modulated square wave control pulses. The relationship between the amplitude of the output and the relative phases of the two square waves applied respectively at A1 and B1 to the two pairs of transistors is sinusoidal, and this is taken into account when preparing the control pulses. Pulse modulation systems.-The output of a carrier wave oscillator O, Fig. 4, is phase shifted and rectified to provide two anti-phase negative half-wave signals to which the modulating signal M is added in units AN1 and AN2. The peak value of the modulating signal does not exceed half the amplitude of the oscillator output signal. The outputs of AN1 and AN2 feed respective trigger circuits T1 and T2 which have a threshold equal to half the amplitude of the half-wave unmodulated signals. The width of the pulse outputs of T1 and T2 depend on the instantaneous amplitude of the modulating signal, and these pulses are differentiated in units D1 and D2. The pulses corresponding to the leading edges of the outputs of T1 and T2 are fed through rectifiers R3 and R5 to a bistable circuit K1 which produces one square wave output at A1. The pulses corresponding to the trailing edges are fed through rectifiers R4 and R6 and inverters U1 and U2 to a second bi-stable circuit K2 which provides the second square wave output at B1, the relative phases of the two square waves depending on the modulation.