| 摘要 |
PURPOSE:To maintain the matching of impedance at an input/output point and at the same time setting the loss due to the coupling and branching at zero, by giving the directivity for the coupling or branching of signals by means of an operational amplifier. CONSTITUTION:Operational amplifiers OPA1 and OPA2 are earthed through their plus terminals via resistances R3 and R10 respectively, and signals are applied to a minus terminal of each of the OPA1 and OPA2 via resistances R1 and R7 respectively. Then feedback resistances R2 and R9 are connected between the minus terminal and an output terminal of the OPA1 and OPA2 respectively. In such a way, an inverted amplifier is obtained. Then the sufficient negative feedback is applied to the inverted amplifier to reduce the input impedance down to such a level that can be virtually neglected. In the same way, the output impedance is also reduced down to a low level. The voltage gain is substantially decided by the ration between R2/R1 and R9/R7 and therefore can be set freely. The resistances R4-R6 form a resistance hydrid. Then the matching of impedance is obtained by setting the resistances R1 and R4-R6 at R0 and the resistances R7 and R8 at 5/2R0 respectively in case the load impedances of terminals A, B and C are set at R0. |
