An S-band MMIC linear-in-dB wide-dynamic-range variable gain amplifier with matching compensation

This paper describes a method to design compact linear-in-dB variable gain amplifiers (VGAs) with good matching in a wide dynamic range. The method is theoretically supported and has been validated with the design of a fully monolithic VGA. Several circuits have been tested and excellent agreement between the measured and predicted results has been achieved. The maximum gain is 18.8 dB with 40 dB dynamic range under a low control voltage from -0.4 V to -1.5 V. Measured output 1 dB compression is 12 dBm at maximum gain with associated third order intercept point better than 22 dBm. 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 2×1.0 mm² and consumes only 34 mA from a supply voltage of 3.5 V.