A 25 MHz 20 dB variable gain amplifier

This paper describes a new special purpose variable gain amplifier (VGA) using a standard 1.2 μm digital CMOS process. The new architecture allows the gain to be varied over a wide range (more than 20 dB), while temperature induced drift in gain is kept very small over a wide temperature range (5°C to 70°C). With the new VGA architecture, bandwidth is almost independent of gain. Despite low power consumption (19 mW) the circuit has a large bandwidth (27 MHz), a high maximum gain (14), and shows low THD (better than -55 dB) over its full frequency range. The circuit does not use any capacitor for gain adjustment, thus it is very compact (0.28 mm×0.25 mm) and has a large input impedance (transistor gate)