A multi-mode complex bandpass filter with gm-assisted power optimization and I/Q calibration

Abstract

This paper presents a 65nm multi-mode complex band-pass filter (C-BPF) used in low-IF GNSS receivers. It supports the bandwidth of 4MHz, 10MHz and 18MHz, and can be centered at 4.2MHz, 6.1MHz, 12.3MHz and 28MHz. The OTAs served in the filter are realized in arrays which makes the power consumption scalable among different operation modes. In addition, assistant transconductors (assistant-gm) are adopted to compensate the outputs of each OTA stage, which in turn saves at maximum 9mA DC current for the whole filter. In order to achieve higher than 30dB image rejection ratio (IRR), another group of assistant-gms are introduced to the input stage for I/Q mismatch calibration, which is able to regulate a maximum ±3dB amplitude imbalance and ±5° phase imbalance. The filter consumes less than 10mA in the 28MHz-IF, 18MHz-bandwidth mode, and achieves >31dB IRR with the maximum I/Q amplitude and phase mismatch.