ABSTRACT
This chapter describes the variable gain amplifier (VGA) used in the radio frequency integrated circuit (RFIC) transceiver. The VGA is a key RF frontend building block that supports reliable mobile communication of wireless transceivers. The range of the VGA gain control also determines the receiver input dynamic range that provides a stable regulated power to the baseband chipset. The gain control can be achieved by either discrete steps (digital variable gain amplifier (DVGA) or programmable gain amplifier (PGA)) or by continuous gain variation (VGA). The DVGA implemented by using bipolar transistors have exponential transconductance characteristic based on the bias voltage and have a linear transconductance characteristic based on the bias current. A DVGA can be implemented at circuit level by switching between fixed gain amplifier stages or by using a binary weighted array of passive or active circuit components selected discretely using transistor switches.
