Patent GB-1474951-A (GB)
Title: Linear power amplifying systems for providing modulated carrier signal outputs
IPC: H03F1/02
Filed: 1974-03-28
Abstract: 1474951 Amplifiers N O SOKAL and A D SOKAL 28 March 1974 [28 March 1973] 12329/74 Headings H3W and H3T In a linear power amplifying system the amplitude of the output signal of a power amplifier 1, Fig. 2, is controlled by the output of a differential amplifier 10 which has one input connected to the input of the amplifier by an amplitude detector 5 and its other input connected to the output of the amplifier by an attenuator 3 and an amplitude detector 2 and the attenuator is connected between the output of the power amplifier and the input of the amplitude detector 2.  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 underwater or sonar transmitters. As shown in Fig. 2 the output from the 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. The 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. 3, not shown) fed from input 18 via an inverter (23) and flipflop (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 R.F. induction heater. Power output control of power amplifier 1 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 direct-coupled regulator, an arc-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 controlled so as to obtain a voltage switching Class D power amplifier. An example of which employs alternately operating transistor switches (S1, S2, Fig. 4A, not shown) 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 driven circuit. Specification 1,474,952 referred to.