Matsushita Electric Industrial Co., Ltd.

Hirokazu Mori

Yusaku Tada

While a switch SWis connected to 'a'-terminal side, offset of a differential output voltage 'A&#x2212;' of a D/A converter() is held in a comparator, and is reflected to a reference voltage. Thereafter, the switch SWis switched to a &#x201c;b&#x201d;-terminal side, and offset of a differential output voltage &#x201c;A+&#x201d; of the D/A converter() is measured by the comparator. An error signal is outputted to a counterso as to count up the counter. Such an operation is repeatedly carried out in which the count value is added to 1.7 V and then the added count value is inputted into the D/A converter(), and such a count value latched in a latch at timing when the error signal is inverted is defined as an offset correction value.

Comparing circuit and offset compensating apparatus

A comparator with an offset canceling function and a D/A conversion apparatus capable of canceling an input/output offset with high accuracy using this comparator. To eliminate unbalance between right and left currents of the differential circuit making up the comparator, the phase of a single end output signal of the differential circuit is inverted and the inverted signal is fed back to one substrate of the differential pair MOS transistors as a substrate bias. Threshold voltages of the MOS transistors are changed and the current capacities of the transistors are adjusted in this way.

Growing community of inventors

Kawasaki, Japan

Hirokazu Mori