Compact Variable Gain Amplifier for a Multistandard WLAN/WiMAX/LTE Receiver

This paper presents a novel single-stage VGA architecture that employs two Gm cells, a voltage-controlled current attenuator, resistors and capacitors. The gain can be changed in three large steps by using digital controls, and continuously within these steps. The VGA bandwidth and output-related IP3 and 1dBCP are independent of the gain setting; the bandwidth can be programmed through a digitally-controlled capacitor array placed at its output. The proposed architecture was employed to realize the VGA for a WLAN/WiMAX/LTE radio receiver. Die area and power consumption were reduced by implementing the two Gm cells with one instantiation of a high-linearity Gm-core and scaled outputs; also, the current attenuator was implemented with a simple differential current steering circuit; finally, the load resistors were also used to sense the output common-mode level. The VGA was fabricated in 0.15 um standard CMOS process. Measurement results show the gain varying between -5 dB to 30 dB and the max bandwidth surpasses 60 MHz; 11.14 nV/√{Hz} input referred noise; O1dBCP of 8.6 dBm while taking 4.2 mA from a 1.8 V supply; it settles within 20 ns after a min-max step-change of the gain; it occupies 0.05 mm².