Patent ID: 6597224
Filing Date: 2003-07-22
Classification: H03K

Abstract:
A hysteresis comparing device with constant hysteresis width, for separately 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, wherein the threshold voltage generator comprises: a bandgap reference voltage generator, used to produce a bandgap reference voltage; a transconductance amplifier, coupled to the bandgap reference voltage generator, in which an positive input terminal of the transconductance amplifier is used to receive the bandgap reference voltage; a transistor, wherein a gate electrode of the transistor is coupled to an output terminal of the transconductance amplifier, a source region of the transistor is coupled to a negative input terminal of the transconductance amplifier; a reference resistor, wherein one terminal of the reference resistor is coupled to the source region of the transistor, and another one terminal of the reference resistor is coupled to a ground voltage, wherein a current flowing through the reference resistor is a reference current, and a quantity of the reference current is a result of the bandgap reference voltage divided by the reference resistor; a first current mirror, wherein a first terminal of the first current mirror is coupled to a drain region of the transistor and used to receive the reference current, a second terminal of the first current mirror is to produce a first mirror current according to the reference current, and a third terminal of the first current mirror is to produce a second mirror current according to the reference current; a second current mirror, wherein a first terminal of the second current mirror is coupled to a second terminal of the first current mirror and used to receive the first mirror current, a second terminal of the second current mirror is to produce a second mirror current according to the first mirror current; a first resistor, wherein one terminal of the first resistor is coupled to the third terminal of the first current mirror, and a voltage thereof is the upper threshold voltage, another terminal of the first resistor is used to receive the first signal; and a second resistor, wherein one terminal of the second resistor is coupled the another terminal of the first resistor, a second terminal of the second resistor is coupled to the second terminal of the second current mirror, and a voltage of the second terminal of the second resistor is 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 one selected from the upper threshold voltage and the lower threshold voltage; and a next stage comparator for outputting the digital signal, wherein one terminal of the next stage comparator is used to receive the multiplexing signal, and another terminal is used to receive the second signal.