Quantization circuit for image data transmission system

A signal receiver quantization circuit for an image data transmission device in which received signals are quantized correctly even if they are subjected to distortion in their time positions so that degradation of the received images is prevented. In accordance with the invention, a signal receiver includes a digital PLL circuit, a PLL control circuit for detecting the transition times of an input received signal with the digital PLL circuit being controlled in accordance with an output of the PLL control circuit, and a circuit for sampling the input signal in response to an output signal of the digital PLL circuit. In a preferred embodiment, the PLL control circuit detects the transition times of the input signal only during predetermined time slots determined in accordance with the relative phase between the input received signal and a sampling clock.