| 摘要 |
The first branch includes first (16) and third (20) mixers and the second branch includes second (17) and fourth (21) mixers. A first local oscillator (26) provides a local oscillator signal to the first mixer and its quadrature component to the second mixer. A second local oscillator (30) is coupled to the third mixer and through a quadrature phase shifter (32) to the fourth mixer. The third and fourth mixers are coupled to the first and second mixers respectively to receive a down-converted signal from them. The sum and difference of the signal at the outputs of the third and fourth mixers is derived in a respective summer, differencing circuit (22, 24). Circuits for correcting gain and phase errors in the signal paths are coupled to the summer and differencing circuit, for transforming their outputs to provide signals having terms centred on 2 delta w, where delta w equals w1-ee, wc is the carrier frequency and w, is the frequency of the first local oscillator.4
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