Importance

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Abstract

Analog (LC) circuit components for an input matching and base charge removal network for a Class-C amplifier are replaced by a digitally driven shunt circuit, which is coupled between the base electrode of the Class-C power transistor and a reference voltage terminal (ground). The digitally driven shunt circuit is operative to couple the base electrode of the power transistor to the reference voltage terminal upon the termination of the limited duty cycle input pulse employed as the base drive to the power amplifier. To facilitate implementation as a digital application specific integrated circuit (ASIC), the controlled shunt circuit comprises an auxiliary or second bipolar transistor having its emitter-collector path coupled in circuit with the base of the bipolar power transistor and the reference voltage terminal. This second transistor has its base coupled to receive a control pulse, which turns on the shunt transistor hard at the termination of the input pulse, thereby providing a shunt or discharge path for base charge that accumulated on the base of the power amplifier transistor during the input pulse applied to its base. Both the input pulse and the control pulse have a duration on the order of one-fourth of the duty cycle of the output voltage swing. In terms of the period of the output voltage swing, the control pulse is effectively delayed with respect to the input pulse by 90.degree..

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First Claim