USE OF A DC COMPONENT FEEDBACK WITH ON-CHIP FILTERING TO MATCH BETWEEN FREQUENCY CONTROL CIRCUIT AND A SECOND DETECTOR IN A MONOLITHIC INTEGRATED CIRCUIT

摘要

A surface-acoustical-wave (SAW) or other lumped intermediate-frequency amplifier filter is followed by an IF amplifier chain and a second detector constructed within the confines of a monolithic integrated circuit. The IF amplifier chain includes three emitter-coupled differential amplifiers, each exhibiting up to about twentyfold voltage gain, cascaded one after the other. Provision is made for automatically controlling the voltage gain of the first two emitter-coupled differential amplifiers. Common-collector amplifiers are used to buffer the application of the balanced output signals from each of the emitter-coupled differential amplifiers to the succeeding emitter-coupled differential amplifier or second detector. Balanced current responses to the direct bias potentials on which the balanced signals supplied to the second detector are respectively superposed, are extracted by lowpass filtering that is on-chip and does not use off-chip IF bypass capacitors. These balanced current responses are fed back to the emitters of the transistors in the common-collector amplifiers used to couple the first gain-controlled emitter-coupled differential amplifier in the IF amplifier chain to the second gain-controlled emitter-coupled differential amplifier in the IF amplifier chain. This completes a direct-coupled feedback loop for degenerating the differences between the direct bias potentials on which the balanced signals supplied to the second detector are respectively superposed.