Patent ID: 6906568

Claim:
A hysteresis comparing device with constant hysteresis width, for receiving a first signal and a second signal and outputting a digital signal, the hysteresis comparing device comprising: a threshold voltage generator used to receive the first signal and output an upper threshold voltage and a lower threshold voltage, the threshold voltage generator comprising: a bandgap reference voltage generator, used to produce a bandgap reference voltage; a reference resistor for generating a reference current according to the bandgap reference voltage; a current mirror for generating a second mirror current according to the reference current; a first resistor and a second resistor connecting in series for receiving the first signal and the second mirror current, and outputting the upper threshold voltage and the lower threshold voltage; a multiplexer, coupled to the threshold voltage generator, and used to receive the upper threshold voltage and the lower threshold voltage, wherein the multiplexer also outputs a multiplexing signal according to the digital signal, and the multiplexing signal is from one of the upper threshold voltage and the lower threshold voltage; and a next stage comparator, wherein one terminal of the next stage comparator is used to receive the multiplexing signal, and another one terminal is used to receive the second signal, and the next stage comparator outputs the digital signal, wherein the first signal is obtained by low-pass filtering the second signal.