CMOS VARIABLE GAIN AMPLIFIER WITH AN APPROXIMATED EXPONENTIAL GAIN CONTROL
Original Publication Date: 2002-Jun-13
Included in the Prior Art Database: 2003-Jun-21
AM9-97-020 CMOS VARIABLE GAIN AMPLIFIER WITH AN APPROXIMATED EXPONENTIAL GAIN CONTROL Variable gain amplifiers are widely used in communication, multimedia and storage systems for providing a signal-processing gain control in their front-end circuits. They are also essential components in circuits that include an analog-to-digital conversion where an optimized operational region is required. A typical variable gain amplifier includes an amplitude modulation amplifier, a control voltage conversion circuit with signal interconnection for providing a variable gain amplification function. FIG. 1 is a simple variable gain amplifier for generating a gain controlled amplification of a differential high frequency input signal Vin. The analog signal Vin with signal terminals Vin+ and Vin- is supplied to the amplifier with an amplitude modulation function to produce a differential output signal Vout with signal lines Vout+ and Vout-. The voltage amplification or attenuation gain G, defined as G Vout Vin, is controlled or modulated by a desired gain control signal Va generated by a voltage conversion circuit. The conversion circuit translates the control voltage Vc which is provided with respect to a reference voltage Vr, and forms an interfacing signal Va. By defining Vr as a ground reference, the overall gain G of the amplifier is a function of Vc.