A CMOS RF Receiver with Improved Resilience to OFDM-Induced Second-Order Intermodulation Distortion for MedRadio Biomedical Devices and Sensors

Abstract

A MedRadio RF receiver integrated circuit for implanted and wearable biomedical devices must be resilient to the out-of-band (OOB) orthogonal frequency division modulation (OFDM) blocker. As the OFDM is widely adopted for various broadcasting and communication systems in the ultra-high frequency (UHF) band, the selectivity performance of the MedRadio RF receiver can severely deteriorate by the second-order intermodulation (IM2) distortion induced by the OOB OFDM blocker. An analytical investigation shows how the OFDM-induced IM2 distortion power can be translated to an equivalent two-tone-induced IM2 distortion power. It makes the OFDM-induced IM2 analysis and characterization process for a MedRadio RF receiver much simpler and more straightforward. A MedRadio RF receiver integrated circuit with a significantly improved resilience to the OOB IM2 distortion is designed in 65 nm complementary metal-oxide-semiconductor (CMOS). The designed RF receiver is based on low-IF architecture, comprising a low-noise amplifier, single-to-differential transconductance stage, quadrature passive mixer, trans-impedance amplifier (TIA), image-rejecting complex bandpass filter, and fractional phase-locked loop synthesizer. We describe design techniques for the IM2 calibration through the gate bias tuning at the mixer, and the dc offset calibration that overcomes the conflict with the preceding IM2 calibration through the body bias tuning at the TIA. Measured results show that the OOB carrier-to-interference ratio (CIR) performance is significantly improved by 4–11 dB through the proposed IM2 calibration. The measured maximum tolerable CIR is found to be between −40.2 and −71.2 dBc for the two-tone blocker condition and between −70 and −77 dBc for the single-tone blocker condition. The analytical and experimental results of this work will be essential to improve the selectivity performance of a MedRadio RF receiver against the OOB OFDM-blocker-induced IM2 distortion and, thus, improve the robustness of the biomedical devices in harsh wireless environments in the MedRadio and UHF bands.

A 24 GHz CMOS Direct-Conversion RF Receiver with I/Q Mismatch Calibration for Radar Sensor Applications

“…The I/Q calibration of this work is based on the mixer’s gate bias control for the amplitude tuning, and the LO buffer’s capacitance control for the phase tuning. The proposed gate bias control circuit for the amplitude mismatch calibration can be found in more conventional sub-6 GHz RF receivers such as 0.9/1.9 GHz cellular receiver [ 26 ], 2.4 GHz Bluetooth receiver [ 27 ], and 400 MHz MedRadio receiver [ 28 ]. In addition, the same technique was also proven effective for the 28 GHz millimeter-wave RF transmitter [ 2 ].…”

28-GHz CMOS Direct-Conversion RF Transmitter with Precise and Wide-Range Mismatch Calibration Techniques

“…It can decouple the dc offset cancellation condition and optimal gate bias condition to some extent, and thus allow the finding of the best optimal dc offset cancellation condition while minimally disturbing the dc bias condition. Due to this advantage, this technique was adopted in the author's previous sub-6 GHz CMOS transceiver designs [19,20]. The body bias voltage is precisely generated by a 6-bit voltage digital-to-analog converter (VDAC).…”

Issues with Modeling a Tunnel Communication Channel through a Plasma Sheath

“…The model has been used to conduct a noise immunity investigation for signal-code constructions that meet telemetric and control radio line requirements. For this purpose, estimates for the bit error rate (BER) and signal-to-noise ratio (SNR) were included in the model (that is very common for a variety of tasks) [ 20 , 21 , 22 , 23 , 24 , 25 ]. SNR was estimated as the ratio of the spectral power density in the band of the signal to the spectral power density outside this band.…”