This brief presents a baseband automatic gain control (AGC) circuit for an IEEE 802.11a wireless local area network (WLAN) direct conversion receiver. The whole receiver is to be fully integrated in a low-cost 0.25-µm 75-GHz SiGe bipolar complementary metal-oxide-semiconductor (BiCMOS) process; thus, the AGC has been implemented in this technology by employing newly designed cells, such as a linear variable gain amplifier (VGA) and a fast-settling peak detector. Due to the stringent settling-time constraints of this system, a feedforward gain control architecture is proposed to achieve fast convergence. The proposed AGC is composed of two coarse-gain stages and a fine-gain stage, with a feedforward control loop for each stage. It converges with a gain error of below ±1 dB in less than 3.2 µs, whereas the power and area consumption are 13.75 mW and 0.225 mm 2 , respectively. IndexTerms-Bipolar complementary metal-oxidesemiconductor (BiCMOS) integrated circuits, feedforward systems, gain control, peak detector, variable gain amplifier (VGA), wireless local-area network (WLAN).

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This paper presents a new low-voltage pseudodifferential continuous-time CMOS transconductor for wideband applications. The proposed cell is based on a feedforward cancellation of the input common-mode signal and keeps the input common mode voltage constant, while the transconductance is easily tunable through a continuous bias voltage. Linearity is preserved during the tuning process for a moderate range of transconductance values. Simulation results for a 0.35 µm CMOS design show a 1:2 G m tuning range with an almost constant bandwidth over 600 MHz. Total harmonic distortion figures are below -60 dB over the whole range at 10 MHz up to a 200 µA p-p differential output. The proposed cell consumes less than 1.2 mW from a single 2.0 V supply. I. 1-4244-0921-7/07 $25.00 © 2007 IEEE.

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