In a phase modulation method enable signals may be sequentially generating based on a clock signal to generate a sequence of enable signals, and a signal is delayed by delay values generated from delay cells based on the sequence of enable signals and digital bit values. A phase modulator may include a first delay circuit configured to: delay a clock signal based on a first delay value to generate a first delayed clock signal, and delay a carrier signal based on the first delayed clock signal to generate a first delayed carrier signal; and a second delay circuit configured to: delay the first delayed clock signal based on a second delay value to generate a second delayed clock signal, and delay the first delayed carrier signal based on the second delayed clock signal to generate a second delayed carrier signal.