Patent GB-1474952-A (GB)
Title: Amplifying and processing systems for providing modulated carrier signal outputs
IPC: H03F3/217
Filed: 1974-03-28
Abstract: 1474952 Amplifiers; pulse modulation systems; compressors N O SOKAL and A D SOKAL 28 March 1974 [28 March 1973] 53996/76 Divided out of 1474951 Headings H3W H3T H4L and H4R In an amplifying and processing system for providing a modulated carrier signal output, input and output signals from a power amplifier 1, Fig. 2, are compared at 4 to control the amplitude of the carrier signal output of the power amplifier by controlling the A.C. cycle duty ratio of a switching mode stage of the power amplifier. The amplifier 1 for amplitude modulated carrier and single side band signals can be used as RF power amplifiers for radio communications or transmitting systems or ultrasonic frequency power amplifiers for under water or sonar transmitters. Further the amplifier may provide an amplitude or phase modulator or amplitude compressor. As shown in Fig. 2 the output from a differential amplifier 4 provides an error signal to a power output control 8 controlling the amplifier 1 to provide the required output amplitude by means of a feedback arrangement which functions to reduce amplitude distortion. An attenuator 3 can be inductively, capacitively or transformer coupled to the output. The output from a modulator is fed to the input 7 which can be changed in frequency in a frequency translator 9. The output 13 is also applied as feedback to a control mechanism 11 which controls a variable phase shift network 17 to reduce phase distortion by maintaining zero phase shift between input and output of the amplifier. The control mechanism 11 includes a phase detector 27, Fig. 5, fed from input 19 via an inverter 23 and a flip-flop 25 and fed from output 13 via a flip-flop 29. The amplifier output can be converted to light for optical communication or heat for an RF induction heater. A function generator (33, Fig. 4, not shown) may be connected in the input or output path to inputs a or b of the differential amplifier 4 so as to provide a power amplifier having a desired amplitude transfer function. In a modification of the control of the amplifier 1, Fig. 5, the differential amplifier 4 is replaced by a RF subtractor 37 or adder and a synchronous detector 39. In a modification (Fig. 6, not shown) the inputs to the RF subtractor 37 are also fed to a limiter/3-state digital adder (41) which provides a reference phase input to a 3-state synchronous detector (43) fed with the output from the RF subtractor. In a further modification (Fig. 7, not shown) the output from a 3-state synchronous detector (49) of a similar circuit to (Fig. 6, not shown) but using a RF adder is fed to the input of a summer (51). The other input of the summer (51) is fed with the output from the 3-state synchronous detector (43) and the output from the summer (51) controls the power output control 8. In a still further modification (Fig. 8, not shown) frequency translators (53, 57 and 55, 59) feed the inputs to the RF subtractor 37. In addition to the A.C. duty ratio control of a switching stage of the power amplifier the power output control 8 can be by control of the D.C. power supply for the output stage of the power amplifier and can be for one or more earlier stages by means of a switching regulator such as a transistor and a diode, a dissipative directcoupled regulator, an A.C.-coupled Class B, Class AB or Class A modulator and a switching regulator augmented for response to higher modulation frequency by addition of an A.C.- coupled Class B, Class AB or Class A modulator examples of which are disclosed. (Fig. 1A, not shown) discloses a power output control 8 including a modulator (8A) controlling a switch (8B) regulating the D.C. supply (8C) to one or more stages of the power amplifier 1. The RF cycle duty ratio of one or more of the RF power output transistors or electron tubes can be obtained by a voltage switching Class D power amplifier. An example of which employs alternately operating transistor switches S1, S2, Fig. 9A, with a further transistor switch S3 being on during the time when switches S1 and S2 are both off. The D.C. bias level or the RF input drive magnitude supplied to the control electrode of a transistor or electron tube such as a pentode or tetrode of one or more stages of the RF amplifier 1 can be controlled. A controlled RF attenuator such as a PIN diode can be inserted in the drive circuit. Specification 1,474,951 is referred to.