A Center Frequency Calibration Technique for Ring VCO Exploiting Delay−1 Detection

This paper presents a technique to detect and correct the variation of the center frequency of ring voltage-controlled oscillator (VCO) with process, voltage and temperature (PVT). Instead of using frequency information, delay information is employed for calibration to achieve background operation without replicas for saving power and hardware consumption. Since the delay expresses a reciprocal relationship to oscillation frequency, a delay
⁻¹
detector is proposed to calculate the polarity of the deviation of the center frequency. Designed in 180 nm CMOS, a 15-stage ring VCO with deviated initial center frequency can be effectively calibrated by the proposed technique.