A phase detection system includes a low-resolution sensor and a high-resolution sensor for monitoring an alternating current (AC) voltage. A phase detector receives voltage samples from both the low-resolution sensor and the high-resolution sensor. The phase detector monitors the low-resolution sensor to detect approaching zero cross events (i.e., monitored voltage values approaching zero). In response to an approaching zero-cross event, the phase detector uses the magnitude of the high-resolution voltage samples measured on either side of the zero cross event to determine the phase of the monitored AC voltage.