Voltage controlled amplifier for symmetrical electrical signals

Claim 1

A voltage controlled, ground symmetrical amplifier comprising: a logarithm circuit comprising a first pair of bipolar transistors and circuit means connecting the emitter-collector paths of said first pair of transistors, an antilog circuit comprising a second pair of bipolar transistors and circuit means connecting the emitter-collector paths of said second pair of transistors, means connected for applying a gain control voltage to the bases of one of said first pair of transistors and one of said second pair of transistors, a bipolar auxiliary transistor having an impedance in the emitter-collector path thereof, means connected for applying to the base of said auxiliary transistor a constant direct voltage, which is temperature stabilized over the operating range of the amplifier and whose value is approximately equal to U beO +α·273°/mV where U beO =the base-emitter voltage across the p/n or n/p junction at 0° C. and with operating collector and emitter current, and α=the temperature coefficient of this base-emitter voltage, whereby the auxiliary voltage appearing across said auxiliary transistor impedance is directly proportional to absolute temperature, means connected for thermally coupling said auxiliary transistor to said first and second pair of transistors, circuit means connected for applying said auxiliary voltage to the base of the other of said second pair of transistors, whereby the output signal from said antilog circuit is ground symmetrical over at least a range of ±30°, and means connected for generating said gain control voltage as a product voltage containing said auxiliary voltage as a factor.