An automatic frequency tuning loop for the low pass filter of 400–800 MHz Spectrum sensing system

An automatic frequency tuning loop (ATL) for the low pass filter is fabricated in TSMC 0.18-μm CMOS technology for 400-800 MHz Spectrum Sensing. The whole ATL system employs a divide-by-four, a low pass filter, a phase-frequency-detector (PFD), charge pump (CP), a comparator and a successive approximations register (SAR) to calibrate the low pass filter of 400-800 MHz spectrum sensing system. The ATL provides 3.33% corner frequency accuracy. The ATL operates in the range from 207 kHz to 350 kHz, and the frequency steps are from 8 kHz to 10 kHz.