GB1285685A - Improvements in or relating to transistor amplifiers - Google Patents

Abstract

1285685 Transistor amplifying circuits MARCONI CO Ltd 24 May 1971 [3 Sept 1970] 42207/70 Heading H3T In a transistor amplifier including at least one transistor which in operation produces at least the third harmonic of a fundamental frequency applied to the input terminal of the amplifier, voltage limiting means are provided for modifying the phase of at least the third harmonic frequency component of voltage present at the collector of said transistor in relation to the fundamental frequency component of voltage there present substantially without changing the amplitude of said fundamental frequency component whereby the application of excessive voltage to said transistor as a result of third harmonic generation thereby is prevented. Transistors 1, 2 operate in class AB, being driven with high frequency from a transformer 3; the output is taken via transformer 4, a line 6 and a filter 5 tuned to reject third harmonic. Limiting diodes 9, 10 are connected to the collectors of transistors 1, 2 respectively, with their common terminal connected to a biasing terminal 12 and via capacitor 11 to earth. the arrangement is such that the diodes do not clip the fundamental frequency, but only the harmonics which have become phase-shifted by the line 6 and filter 8. The effect of limiting is to shift the phase of the third harmonic.