11.2 A Blocker-Tolerant Receiver with VCO-Based Non-Uniform Multi-Level Time-Approximation Filter with −36dB EVM in 28nm CMOS

The growing demand for wirelessly connected devices and networks has resulted in increasingly crowded spectrum, and hence blocker-tolerant receivers have drawn more attention. The undesired signals present at the frequencies other than the desired band, often referred to as out-of-band (OOB) blockers, can degrade in-band EVM of the receiver after sampling. Therefore, analog filtering along the receiver path is often needed to attenuate blockers and preserve the desired signal quality. While low-order analog filters can mitigate far-out blockers, nearby blockers require high-order bandpass or notch filtering. Prior high-order analog filter designs [1]–[11] have been demonstrated but are often limited in reconfigurability in terms of changing filter response or passband/notch frequencies. On the other hand, a mixer-first receiver with a time-approximation-filtering (TAF) technique [12] offers tunable bandpass/notch filtering by judiciously controlling when to integrate the input signal, i.e. time-gated integration according to a TAF pattern. It avoids costly switched-capacitor or resistor arrays and hence significantly lowers the implementation cost. Moreover, this TAF receiver allows non-uniform (NU) sampling to further mitigate the potential blockers appearing at harmonics of the sampling frequency, i.e. alias-band blockers. However, the achievable blocker rejection is still limited by the TAF pattern. To further enhance the overall blocker tolerance while maintaining high reconfigurability, we propose (1) a multilevel time-approximation filtering (mTAF) to provide more rejection for multiple blockers, (2) a VCO-based integrator with embedded digitalization to improve the accuracy of the TAF response at lower cost, (3) judiciously combining N-path filtering and NU sampling operations to simultaneously reject both far-out and alias-band blockers. A proof-of-concept receiver prototype was fabricated in 28nm CMOS, achieving maximum 65dB blocker rejection and EVM of −36/-31dB in the presence of a −20/+24dBc blocker at 1.217GHz frequency offset from a 32GHz LO frequency. Compared to prior N-path-filter receivers and TAF receivers, the non-uniform multilevel TAF receiver shows nearly 20dB improvement in nearby blocker rejection.