A wide-frequency and high-precision ZQ calibration circuit for NAND Flash memory

This paper presents a wide-frequency and high-precision ZQ calibration circuit for NAND Flash memory. To achieve high-precision impedance calibration within the wide frequency range of NAND Flash memory, the proposed ZQ calibration circuit adopts dynamic comparator with offset voltage compensation to accurately control the equivalent impedance of driver. And to ensure that the offset voltage of comparator can be accurately compensated in a wide frequency range, the offset voltage compensation circuit is controlled by a charge pump whose charging and discharging step time can be adjusted based on operating frequency range. The proposed circuit is fabricated in 130 nm CMOS process. In the frequency range of 1 MHz to 200 MHz, the Monte-Carlo analysis results show that the standard deviation of offset voltage is within 0.18 mV and the standard deviation of targeting calibrated impedance on 300 ohm is within 3.5 ohm. And the chip testing results show that the proposed ZQ calibration circuit can achieve 1.5% calibration accuracy.