CONSTANT CURRENT SOURCE CIRCUIT

摘要

PURPOSE:To prevent the characteristic variance of a transistor TR as well as the current variance of a constant current source due to the temperature change, by detecting the drain current flowing to the TR and controlling the gate voltage of the TR so that said drain current is kept at a fixed level. CONSTITUTION:The drain current ID of a transistor TRM1 is detected as the voltage value obtained between both terminals of a capacitor in a switched capacitor circuit. This voltage value is sampled and held by a sampling/holding circuit 2 and then compared with the reference voltage value set previously and received from a reference voltage generating circuit 3 via a comparator 4 for decision of the level of the current ID. Then the gate voltage of a 2nd TR, i.e., the gate voltage of the TRM1 is controlled according to the level of the current ID. Thus the current ID is kept at a fixed level. In such a way, a current of a fixed level is obtained regardless of the characteristic variance or the temperature dependence of the TRM1.