A software-defined radio receiver is designed from a low-power ADC perspective, exploiting programmability of windowed integration sampler and clock-programmable discrete-time analog filters. To cover the major frequency bands in use today, a wideband RF front-end, including the low-noise amplifier (LNA) and a wide tuning-range synthesizer, spanning over 800 MHz to 6 GHz is designed. The wideband LNA provides 18-20 dB of maximum gain and 3-3.5 dB of noise figure over 800 MHz to 6 GHz. A low 1/f noise and high-linearity mixer is designed which utilizes the passive mixer core properties and provides around +70 dBm IIP2 over the bandwidth of operation.The entire receiver circuits are implemented in 90-nm CMOS technology. Programmability of the receiver is tested for GSM and 802.11g standards.

Abstract-The implementation of orthogonal frequency division multiplexing (OFDM)-based physical layers suffers from the effect of In-phase and Quadrature-phase (IQ) imbalances in the front-end analog processing. The IQ imbalances can severely limit the achievable operating signal-to-noise ratio (SNR) at the receiver and, consequently, the supported constellation sizes and data rates. In this paper, the effect of IQ imbalances on OFDM receivers is studied, and system-level algorithms to compensate for the distortions are proposed. The algorithms include post-fast Fourier transform (FFT) least-squares and least mean squares (LMS) equalization, as well as pre-FFT correction using adaptive channel/distortion estimation and special pilot tones to enable accurate and fast training. Bounds on the achievable performance of the compensation algorithms are derived and evaluated as a function of the physical distortion parameters. A motivation is included for the physical causes of IQ imbalances and for the implications of the approach presented in this paper on designing and implementing wireless transceivers.Index Terms-Compensation algorithms for analog impairments, equalization, in-phase and quadrature-phase (IQ) imbalances, orthogonal frequency division multiplexing (OFDM).

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