chapter  2

Feedback Amplifier Configurations

WithJohn Choma

This chapter examines small-signal performance equations, general operating characteristics, and engineering design guidelines for the six most commonly used global feedback circuits. These observations derive from analyses based on the judicious application of signal flow theory to the small-signal model that results when the subject feedback network is supplanted by an appropriate two-port parameter equivalent circuit. The chapter utilizes two types of global dual-loop feedback architectures are used: the series-series/shunt-shunt feedback amplifier and the series-shunt/shunt-series feedback amplifier. Although only bipolar technology is exploited in the analysis of the aforementioned four single-loop and two dual-loop feedback cells, all disclosures are generally applicable to metal-oxide-silicon, heterostructure bipolar transistor, and III–V compound metal-semiconductor field-effect transistor technologies. Although the series–shunt circuit functions as a voltage amplifier, the shunt–series configuration is best suited as a current amplifier. The shunt–shunt nature of the subject amplifier suggests the propriety of y-parameter modeling of the feedback network.