| 摘要 |
An image reject circuit comprises a local oscillator (26) for producing a local oscillator signal. A tunable phase shifting network (29) has inputs (1, 3) for receiving the local oscillator signal and producing an output in-phase (I) signal (13, 25) and an output quadrature (Q) signal (15, 27). A first amplitude detector (33) determines the amplitude of the output (I) signal, while a second amplitude detector (35) determines the amplitude of the output (Q) signal. A comparator (37) determines the difference between the amplitudes of the output (I) and (Q) signals, to produce a tuning signal for tuning the phase shifting network (29) to bring the difference between the amplitudes of the output (I) and (Q) signals towards a desired level. Preferably, the tunable phase shifting network (29) (shown in Figure 4) comprises a combination of tunable capacitive, resistive and inductive elements.
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