Provided is a nonvolatile memory including a receive buffer configured to generate a buffer signal by comparing an input signal with a reference voltage, a reference voltage calibrator configured to generate a calibrated reference voltage code signal based on a reference voltage code signal and the buffer signal, and a reference voltage generator configured to generate a reference voltage corresponding to the calibrated reference voltage code signal. In addition, the read reference voltage calibrator includes a duty cycle monitor configured to generate a monitoring signal by measuring a duty cycle of the buffer signal, an up/down counter configured to generate a count number signal by comparing a reference duty cycle with a measurement duty cycle corresponding to the monitoring signal, and a code calculator configured to generate the calibrated reference voltage code signal based on the count number signal and the reference voltage code signal.