A Wideband dB-Linear VGA With Temperature Compensation and Active Load

Abstract

In this paper, a wideband accurate dB-linear variable-gain amplifier (VGA) is presented, which consists of three cascading gain stages with dc-offset cancellation. Based on duplicate biasing and active load techniques, this VGA achieves merits such as simple and accurate continuous dB-linear gain control, gain robustness to process and supply voltage variation and constant bandwidth at different gain settings. The dB-linear gain control is realized based on exponential current steering. The exponential conversion can be based on bipolar transistors or MOS transistors in subthreshold region. Both ways are implemented in this design for comparison purpose. With temperature compensation circuit, this VGA is insensitive to temperature variation. All gain stages of the VGA share the same biasing, exponential V-I conversion and temperature compensation circuits to reduce design complexity. This proposed VGA is fabricated in 55-nm CMOS technology with a core area of 0.033 mm2. The measurement results show the proposed VGA has a dB-linear gain-control range from −37dB to 14 dB with an error within 0.65 dB. The −3dB bandwidth of the VGA is 740 MHz and is nearly constant when the gain varies. The core VGA circuit consumes about 2.49 mW. The proposed design features wide bandwidth, small chip area, and low power consumption.