| 摘要 |
PURPOSE:To realize a current switching circuit which reduces base currents of transistors (TR) constituting differential amplifiers of the current switching circuit and suits to fast operation by providing the differential amplifier as the 1st and the 2nd differential amplifiers separately. CONSTITUTION:The TRs Q7 and Q8 constituting the constant current source circuit 100 are connected on Darlington basis; the base of the TRQ7 is connected to the output voltage terminal 5 of an operational amplifier OP, the emitter is connected to the base of the TRQ8, and the collector is connected to the emitters of TRs Q1 and Q2 constituting the 1st differential amplifier 90a. Those differential amplifiers 90a and 90b are composed of the single-connected TRs, so even when those TRs turn off, charges accumulated in those TRs are discharged speedily from a digital input terminal 1 and a bias voltage input terminal 4, so that fast operation is obtained.
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