A Closed-Loop Reconfigurable Analog Baseband Circuitry With Open-Loop Tunable Notch Filters to Improve Receiver Tx Leakage and Close-in Blocker Tolerance

This brief presents an analog baseband (ABB) circuit in a 0.13 \boldsymbol{\mu }\text{m} SiGe technology for transmitter leakage cancellation and close-in blocker suppressions in fully duplex (FD) frequency-modulated continuous-wave (FMCW) radar. This ABB comprises a programmable gain amplifier (PGA) and a cascaded LPF/Notch hybrid, which incorporates a closed-loop (CL) reconfigurable low-pass filter (LPF) and an open-loop (OL) tunable notch filter. The adopted key topologies include active-R-C bi-quads and \text{G}_{\mathrm{ m}} -C ones. In an FD FMCW transceiver, Tx leakage and close-in blockers are difficult to be eliminated in the RF domain, especially when leakage/blockers are very close to desired signals or even in-band in the frequency domain. This LPF/notch hybrid is proposed to solve this issue. The LPF and PGA provide bandwidth (BW)/gain programmability, while the \text{G}_{\mathrm{ m}} -C bi-quad provides adaptable center frequency for a notch filter. With this adaption, the notch filter could be adjusted to match the leakage/blocker offset frequency. Thus, digitally discrete programmability and analog continuous tuning capability are combined in this solution for improving the overall front-end interference robustness without de-sensitizing the Rx. Furthermore, the order of LPF/notch hybrid is programmable from 2 to 10 with a step of 2 for different rejection levels of interferences. The measured chip achieves a −3dB bandwidth of 6 ~ 21 MHz with 4-bit digital control and 1 MHz/step programmability, and a voltage gain of 0 ~ 70 dB with 9-bit digital control (3-bit from pre-amplifier, and 6-bit from PGA with 1 dB/step). With the condition of 15 dB gain, output P −dB is 11.8 dBm@3MHz, and the output IP3 is 20.8 dBm@3MHz.