Automatic frequency-calibrated low-pass filter with DC offset cancellation

Abstract

In order to improve the LO leakage caused by the DC offset of the analog baseband signal in the direct conversion transmitter, and the drift of the low-pass filter due to process deviation, temperature change, and chip aging, a method of design and implementation of an automatic frequency-calibrated low-pass filter with DC offset cancellation is proposed. In the SPI(Serial Peripheral Interface) control mode, the filter can configure the cut-off frequency from 324 kHz to 648 kHz through the adjustable capacitor array. In the adaptive tuning mode, a digital-analog hybrid calibration structure based on the latched comparator is proposed. By calibrating the RC time constant of the chip, the cut-off frequency is 373. 8~393. 3 kHz under different PVT conditions, and the tuning accuracy relative to the nominal value of 383 kHz is-2. 4%~ 2.7%. The chip uses 0. 18 CMOS technology for tape-out verification, and the tuning circuit area is 0.045 mm2, which is only 2.2% of the main filter area. Under the 1. 8V supply voltage, the power consumption of the whole filter is 6.08 mW, and the input reference noise is 38.49 nV/(Hz)1/2.