| 摘要 |
<p>A method and an apparatus are disclosed for cancelling local oscillator (LO) feed thru in an intermediate frequency (IF) transmission circuit (31). The apparatus includes first and second mixers (15, 17) for receiving local oscillator (LO) and intermediate frequency (IF) signals. The mixers (15, 17) are operable to upconvert the intermediate frequency (IF) signal while passing an attenuated and phase shifted portion of the local oscillator (LO) signal. Bias regulation circuitry (21, 23) is provided for regulating the attentuation and phase shift of the local oscillator (LO) signal portion passed by at least one of the mixers (15, 17) such that the local oscillator (LO) signal portions are combinable to cancel each other. A coupler circuit (19) is provided for combining the mixer outputs such that the local oscillator (LO) signal portions are substantially cancelled and an upconverted intermediate frequency (IF) signal remains. The bias regulation circuitry (21, 23) may be self-correcting to optimize cancellation of the local oscillator (LO) signal portions (Fig. 2).</p> |
