| 摘要 |
PURPOSE:To obtain a variable impedance circuit featuring an excellent linearity and the reduced temperature dependency by using two sets of differential transistor pairs, PN junction pairs, the current mirror circuit and the feedback circuit which feeds the output back to the input terminal respectively. CONSTITUTION:Instantaneous voltage vin applied to terminal 1 is applied to 1st differential Tr pair 11, and the collector of pair 11 is connected to the base of 2nd differential Tr pair 13 as well as to the emitter of load PN junction pair 12. Pair 13 is connected to current mirror circuit 14, and the output of circuit 14 is connected to the input terminal. The emitters of TrQ11 and Q12 forming Tr pair 11 are connected to 1st control current source 15 via feedback resistance R12 and R13, and the emitter of pair 13 is connected to 2nd control current source 16. Input conductance G becomes as shown by Eq. (9), where the input current is iin, the current of source 15 and 16 are IC1 and IC2, and the feedback resistance is RE (RE = R12 = R13). Thus, the input conductance features linear shape with no dependency on the input signal, and can be controlled by the current ratio of the control current source and with no dependency on the temperature. |
