Controlled gain amplifier

An amplifier, the ratio of its output signal to its input signal being responsive to a control signal, said amplifier comprising:

• first and second terminals having connected therebetween a source of said input signal with a direct current conductive path therethrough;
• a third terminal for application of a reference potential;
• a fourth terminal for supplying said output signal;
• a load direct coupled to said fourth terminal;
• a first transistor being of a first conductivity type, having a base electrode connected to said first terminal, having an emitter electrode connected to said third terminal, and having a collector electrode connected to said fourth terminal;
• a first controlled current source responsive to said control signal to supply a first controlled current to said second terminal;
• diode means connected between said second and said third terminal and poled to conduct said first controlled current, said diode means responding to said first controlled current to develop a substantially direct offset potential thereacross, which offset potential is continually applied without substantial attenuation as quiescent base-emitter potential to said first transistor to control the flow of collector current of said first transistor;
• and
• a second controlled current source responsive to said control signal for supplying a second controlled current applied to said fourth terminal to counteract changes in the quiescent component of said first transistor collector current as supplied to said load.