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

Abstract

A software-defined radio (SDR) receiver with im- proved robustness to out-of-band interference (OBI) is presented. Two main challenges are identified for an OBI-robust SDR re- ceiver: out-of-band nonlinearity and harmonic mixing. V oltage gain at RF is avoided, and instead realized at baseband in com- bination with low-pass filtering to mitigate blockers and improve out-of-band IIP3. Two alternative “iterative” harmonic-rejec- tion (HR) techniques are presented to achieve high HR robust to mismatch: a) an 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 multi- phase 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 /43/51 /53dBm in-band IIP3 while the out-of-band IIP3 is /43/49/54dBm 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 /54/48dB over 40 chips, while the digital AIC technique achieves /56/48dB for the dominating harmonic. The total power consumption is 50 mA from a 1.2 V supply.