Low-Power Variable Gain Amplifier Free of Common-Mode Feedback Circuit

A low-power high-dynamic range digitally controlled variable gain amplifier (VGA) is designed in this paper. First, a novel method for defining the output common-mode voltages of VGA is proposed by adjusting the current of the load resistor according to the change of its resistance to keep the voltage drop across the load resistor unchanged, so that the common-mode feedback circuit is not required for the VGA, resulting in decreased power consumption. Second, coupling capacitors are used between the stages to remove the DC offset, and hence no extra DC offset cancellation circuit is necessary. The VGA is designed and simulated in TSMC 0.18μm CMOS process. Simulation results show that, the VGA dissipates an average current of 504.7μA while achieving 1.16MHz -3dB bandwidth and providing 81dB gain range with 3 dB resolution, and the gain error is less than ±0.65dB.