10-MHz 60-dB dynamic-range 6-dB variable gain amplifier

This paper describes a CMOS 10-MHz Variable Gain Amplifier (VGA) with 60-dB dynamic-range. The gain is continuously tunable over a 6-dB range, with a minimum gain of unity and a maximum gain of two. Continuous gain tuning is accomplished by a novel method of interpolating between 10 taps of a feedback resistor, respectively connected to a fully-differential multi-input-stage operational amplifier. Measured results with a 10-MHz input show THD below -60-dB with a Q-V-pp differential output signal. Third-order inter-modulation distortion, for two equal amplitude tones at 9.5-MHz and 10.5-MHz, remains below -59.17-dBc over all gain settings. The circuit has been fabricated in a 0.8-mu m CMOS process (Hewlett Packard CMOS26G), occupies an area of 0.6x1-mm(2) and dissipates 80-mW.