Patent ID: 6339355
Filing Date: 2002-01-15
Classification: H03F

Abstract:
An offsetting comparator device for determining whether or not a potential difference represented by a differential signal has exceeded on offset voltage, the offsetting comparator device comprising:a master comparator circuit which receives the differential signal as differential input and supplies a sensed current corresponding to the potential difference represented by the differential input; and offset current supply means for supplying an offset current, wherein the offsetting comparator device outputs a current representing a sum between the sensed and offset currents, the offset current supply means comprising: a reference differential voltage generator which receives an intermediate potential, represented by the differential signal, as an input and outputs a reference differential voltage corresponding to the intermediate potential; and a slave comparator circuit which receives the reference differential voltage as differential input and outputs a current corresponding to the potential difference represented by the differential input as the offset current, the slave comparator circuit having the same configuration as the master comparator circuit, wherein each of the master and slave comparator circuits receives the associated differential input at respective parallel gates of p-channel and n-channel transistors, the reference differential voltage generator comprising: a potential generator, which includes a resistor and generates both potentials represented by the reference differential voltage based on the intermediate potential and a voltage drop caused by the resistor; and a current controller for controlling the amount of current flowing through the resistor such that the voltage drop caused by the resistor becomes constant, the potential generator comprises an operational amplifier which receives the intermediate potential as one of the inputs, wherein the resistor connects the other input of the operational amplifier to the output thereof, and wherein the output of the operational amplifier is directly output as one of the potentials represented by the reference differential voltage.