| 摘要 |
PROBLEM TO BE SOLVED: To provide an input changeover circuit that reduces crosstalk so as to improve the S/N ratio of an output signal. SOLUTION: In the input changeover circuit, an operating current is supplied to one of differential circuits by a switching signal among a plurality of differential circuits Q7 and Q8, and Q10 and Q11 receiving the input signals of a plurality of systems to activate the one differential circuit and only the input signal supplied to the operated differential circuit is extracted and outputted. The input changeover circuit includes impedance reduction means Q15 and Q16, R7 and R9, Q17 and Q18, and R8 and R10 provided to each of a plurality of the differential circuits Q7 and Q8, and Q10 and Q11 to decrease the impedance of the inoperative differential circuits except the differential circuit selected by the switching signal so as to significantly reduce the crosstalk through the capacitive coupling by the parasitic capacitance between the bases and emitters of the transistors of the inactivated differential circuits, thereby improving the S/N ratio of the output signal.
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