A quadrant alternate switching phase interpolator includes first and second multiplexer circuits, a phase interpolator circuitry, and a controller circuitry. The first multiplexer circuit outputs one of first and second clock signals to be a first signal in response to first and third bits in a quadrant control code. The second multiplexer circuit outputs one of third and fourth clock signals to be a second signal in response to second and fourth bits in the quadrant control code, and the first, the third, the second, and fourth clock signals are sequentially different in phase by 90 degrees. The phase interpolator circuitry generates an output clock signal in response to the first and the second signals and phase control bits. The controller circuitry performs a bit-shift operation on the phase control bits to adjust a phase of the output clock signal.