A GaAs monolithic linear-in-dB wide-dynamic-range variable-gain amplifier with matching compensation for 1.95-GHz applications
05 February 2005
This paper describes a method to design a compact linear-in-dB variable-gain amplifier (VGA) with good input/output matching in a wide gain-control range. The method is theoretically supported and has been validated with the design of a 1.95-GHz GaAs fully monolithic VGA. Measured maximum gain is 18.8 dB with associated noise figure of 6.3 dB and 40-dB dynamic range with lower than +/-1.5-dB deviation from linearity, under a low control voltage from -0.4 V to -1.5 V. Good linearity with an output 1-dB compression of 12 dBm at maximum gain and associated 3(rd)-order intercept point better than 22 dBm are also shown. The adjacent channel power ratio (ACPR) was measured at the 1.95-GHz WCDMA band, showing values better than -48 dBc at 885-KHz offset and -70 dBc at 1.98-Mhz offset over the whole control range. The chip size is 2 x 1.0 mm(2) and consumes only 34 mA from a supply voltage of 3.5 V. (C) 2005 Wiley Periodicals, Inc.