A multi-mode reconfigurable lowpass/complex bandpass continuous-time sigma-delta (LP/CBP CT ΣΔ) modulator for short range wireless receiver is presented. The proposed modulator could be configured as either 3rd-order lowpass or 2nd-order complex bandpass mode. The flexible amplifiers in the integrators and the comparator preamplifiers are implemented with power optimizing technique to acquire scalable power consumption among different modes. And an automatic tuning circuit is utilized to guarantee the accuracy of intermediate frequency and bandwidth. The modulator has been implemented in 65nm CMOS and achieves 82.7dB peak SNR at 4MHz lowpass mode, and 80.7/82.2dB peak SNR at 1MHz/2MHz complex bandpass mode. Powered by a 1.2-V supply, the modulator consumes 2.96 to 3.48mW, resulting in FOMs of 0.038-0.167pJ/conversion.