A 55 dB range gain interpolating variable gain amplifier with improved offset cancellation

This work presents the design of a 55 dB dynamic range gain interpolating variable gain amplifier (VGA). In such wide dynamic range amplifiers, small input referred offsets in the range of a few millivolts may cause the outputs to rail especially at the higher gain settings. Therefore an offset cancellation circuit is needed. The VGA design including an improved offset cancellation circuit is fabricated as part of a full automatic gain control (AGC) loop on an IBM 0.18 μm BiCMOS 7LM technology. Measurement results are in good agreement with simulations showing that the AGC could track input power changes in the range from -44 to +11 dBm introduced to the VGA's 100 Ω differential input impedance. The VGA has a measured bandwidth of 18 MHz and input referred noise of 3.5 nV/√Hz. It can directly drive a capacitive load of 23 pF consuming 4 mA from a 3V supply.