| 摘要 |
A high impedance circuit capable of operating at a low voltage without narrowing the dynamic range is provided, which includes a first and a second transistors forming differential-pair type circuit, a third and fourth transistors, a pair of collector resistance elements, a resistance element and a pair of current source circuits. The third and the fourth transistors serve as emitter follower circuits which also functions as a DC shift with respect to the differential-pair type circuit, as well as buffer circuits for heightening an input impedance of the first and the second transistors looked from the base side of the third and the fourth transistors. The current flowing in the resistance element is made current-fedback with respect to the resistance elements by the third and the fourth transistors. The input impedance is determined as Z1=V1/i3=(R1xR2)/(R1-R2), and when R1=R2, the high impedance circuit becomes infinite impedance.
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