| 摘要 |
PURPOSE:To obtain a constant current source having a prescribed output current ratio by supplying each output current of plural unit current sources to the 1st or 2nd current output terminal via a switch circuit and controlling the switch circuit via a PROM. CONSTITUTION:The unit constant current sources M1-Mn+1 consisting of MOS transistors TR are produced together with switch circuits S1-S1+1 which supply the output currents of source M1-Mn+1 to an output terminal I or NI. The control signals of circuits S1-Sn+1 are produced by an EPROM1. The circuit S1, for example, is formed differentially with MOSTRMS1 and MS2 and the control signal is applied to the circuit S1 with the output of a NAND gate NA1. A decoder 2 receives an input signal 3 and connects the sources M1-Mn+1 to the terminal I. A writing operation is applied to the EPROM1 so that an n:1 output current ratio is obtained between both terminals NI and I, then secured for a semiconductor constant current circuit.
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