A multi-mode reconfigurable analog baseband with I/Q calibration for GNSS receivers is presented. The baseband circuit consists of an I/Q calibration circuit, a reconfigurable complex band-pass filter (C-BPF) and an AGC loop. It provides I/Q mismatch auto-calibration with the aid of a FPGA. The 3rd/ 5th-order reconfigurable C-BPF supports various bandwidths from 2.2 to 10 MHz and with different center frequencies from 3.996 to 16 MHz. The AGC loop features 5-50 dB gain range and 1 dB step, and digital AGC algorithms. The auto DC-offset cancellation is also integrated on-chip. The analog baseband circuit has been implemented in 180 nm CMOS and consumes 6.5-13 mA variable current thanks to the power scaling technique. The measured image-rejection ratio is 45-55 dB, improved by 22 dB after I/Q calibration.