| 摘要 |
A mixer circuit used in a radio receiver for mixing two frequencies (RF, LO) and providing an intermediate frequency (IF) which is difference of two frequencies (RF-LO) with excellent performance of rejection of an image frequency (RF+LO) has a differential amplifier (2e) for amplifying an input RF signal (RF) to provide amplified output in differential form, and a plurality of differential pairs (2a, 2b, 2c, 2d) for mixing an output of said differential amplifier (2e) and a local signal (LO-I, LO-Q) to provide an output IF signal (IF-I, IF-Q). Each output of the amplified RF signal is commonly applied to inphase branch (I) and quadrature branch (Q) of the differential pairs. Sources of each differential pairs (2a, 2b, 2c, 2d) and sources of said differential amplifier (2e) are coupled with a ground through an impedance circuit (3a, 3b, 3c) which has high impedance for operation frequency (RF, LO) and is short-circuited for D.C. current. A transistor of each differential pairs (2a, 2b, 2c, 2d) is biased independently from a bias of a transistor of the differential amplifier (2e).
|
