Semiconductor device

摘要

A differential amplifier includes a differential circuit section, a gain circuit section amplifying the output of the differential circuit section and outputting the amplified output, and an offset voltage adjusting circuit section carrying out an adjustment so that a voltage equal to the offset voltage of the differential circuit section is added to the input voltage applied across a pair of input terminals and giving the adjusted voltage to the differential circuit section. The offset voltage adjusting circuit section includes a differential pair formed of a pair of MOS-FETs, a MOS-FET forming the load of the differential pair, and two resistor elements each corresponding to one of the MOS-FETs of the differential pair and the load, and giving a voltage equal to the offset voltage to the differential pair. This provides a differential amplifier suitable for detecting the output current of the zero-phase current transformer in an earth leakage breaker.

主权项

1. A differential amplifier comprising:
a pair of input terminals; a differential circuit section carrying out differential amplification of voltages given in a pair; a gain circuit section amplifying an output of the differential circuit section and outputting the amplified output; and an offset voltage adjusting circuit section inserted between the differential circuit section and a pair of the input terminals, the offset voltage adjusting circuit section carrying out an adjustment so that a voltage equal to an offset voltage of the differential circuit section is added to an input voltage applied across the pair of the input terminals and giving the adjusted voltage to the differential circuit section; wherein the offset voltage adjusting circuit section comprises: sixth and seventh transistors forming a second differential pair; an eighth transistor forming a current source of the second differential pair; a ninth transistor forming a load of the second differential pair; a first resistor element inserted between the sixth transistor forming one of the second differential pair and the load; and a second resistor element inserted between the seventh transistor forming the other one of the second differential pair and the load, the first and second resistor elements giving a voltage equal to the offset voltage of the differential circuit section to the second differential pair.