A low power, high dynamic-range, broadband variable gain amplifier for an ultra wideband receiver

摘要

A fully differential Complementary Metal-Oxide Semiconductor (CMOS) VariableGain Amplifier (VGA) consisting of complementary differential pairs with sourcedegeneration, a current gain stage with programmable current mirror, and resistor loads isdesigned for high frequency and low power communication applications, such as an UltraWideband (UWB) receiver system. The gain can be programmed from 0dB to 42dB in 2dBincrements with -3dB bandwidth greater than 425MHz for the entire range of gain. The 3rd-orderintercept point (IIP3) is above -13.6dBm for 1Vpp differential input and outputvoltages. These low distortion broadband features benefit from the large linear range of thedifferential pair with source degeneration and the low impedance internal nodes in thecurrent gain stages. In addition, common-mode feedback is not required because of theselow impedance nodes. Due to the power efficient complementary differential pairs in theinput stage, power consumption is minimized (9.5mW) for all gain steps. The gain controlscheme includes fine tuning (2dB/step) by changing the bias voltage of the proposedprogrammable current mirror, and coarse tuning (14dB/step) by switching on/off the source degeneration resistors in the differential pairs. A capacitive frequency compensationscheme is used to further extend the VGA bandwidth.