Digitally Enhanced Software-Defined Radio Receiver Robust to Out-of-Band Interference

Z. Ru, N.A. Moseley, E. Klumperink, B. Nauta
2009 IEEE Journal of Solid-State Circuits  
A software-defined radio (SDR) receiver with improved robustness to out-of-band interference (OBI) is presented. Two main challenges are identified for an OBI-robust SDR receiver: out-of-band nonlinearity and harmonic mixing. Voltage gain at RF is avoided, and instead realized at baseband in combination with low-pass filtering to mitigate blockers and improve out-of-band IIP3. Two alternative "iterative" harmonic-rejection (HR) techniques are presented to achieve high HR robust to mismatch: a)
more » ... n analog two-stage polyphase HR concept, which enhances the HR to more than 60 dB; b) a digital adaptive interference cancelling (AIC) technique, which can suppress one dominating harmonic by at least 80 dB. An accurate multiphase clock generator is presented for a mismatch-robust HR. A proof-of-concept receiver is implemented in 65 nm CMOS. Measurements show 34 dB gain, 4 dB NF, and +3 5 dBm in-band IIP3 while the out-of-band IIP3 is +16 dBm without fine tuning. The measured RF bandwidth is up to 6 GHz and the 8-phase LO works up to 0.9 GHz (master clock up to 7.2 GHz). At 0.8 GHz LO, the analog two-stage polyphase HR achieves a second to sixth order 60 dB over 40 chips, while the digital AIC technique achieves 80 dB for the dominating harmonic. The total power consumption is 50 mA from a 1.2 V supply. Index Terms-Adaptive interference cancellation, adaptive signal processing, baseband processing, blocker, blocker filtering, CMOS, cross-correlation, digitally assisted, digitally enhanced, harmonic mixing, harmonic rejection, interference mitigation, linearity, LMS, low-noise amplifier (LNA), low-noise transconductance amplifier (LNTA), mismatch, multiphase, multiphase clock, nonlinearity, out-of-band interference, passive mixer, polyphase, receiver, robust receiver, SAW-less, software radio (SWR), software-defined radio (SDR), switching mixer, wideband receiver. A. Out-of-Band Nonlinearity Nonlinearity may generate intermodulation and harmonic distortion falling on top of the desired signal, or may desensitize a receiver due to blockers and produce cross modulation [10] . Without sufficient RF band-selection filtering, the out-of-band linearity can become the bottleneck since OBI is much stronger than IBI. A wideband LNA as used in [1] and [2] amplifies the desired signal and undesired wideband interference with equal 0018-9200/$26.00
doi:10.1109/jssc.2009.2032272 fatcat:axr5qxt5zvc33olm4j2fffkil4