| 摘要 |
A receiver 200 for receiving and demodulating a frequency modulated RF signal by a direct conversion procedure includes an input signal path (101) receiving an RF input signal (x(t)), an I-channel (103) including a first mixer 107 for mixing the RF input signal with an in-phase reference signal to produce an in-phase component (I(t)), a Q-channel 105 including a second mixer 109 for mixing the input signal with a quadrature-phase reference signal to produce a quadrature-phase component (Q(t)). The receiver further includes a compensator for repeatedly measuring and compensating for DC offset produced by the receiver and combined with the input signal component in a respective I and/or Q channel. The compensator estimates 202, 204 a component of the DC offset present in the respective channel (I, Q) by (i) taking a set of N samples of the value of the input signal component in the respective channel; (ii) summing the values obtained for the N samples; and (iii) calculating an average value by dividing the sum by the number N of samples, and a combiner 206, 207 operable to combine with the input signal component an adjustment signal which cancels the estimated DC noise component in the respective channel. The receiver may also include a controller 203 operably coupled to the estimator 202, 205 to provide control signals to indicate when the estimator of the compensator should release the noise value it has estimated. The controller may also indicate an integration time to be used by the estimator of each compensator. The controller may include a detector which assists in control of the estimators by determining a frequency offset between the carrier frequency of the input signal and the reference signal produced by a local oscillator 221. The controller may, via a frequency setter 222, adaptively adjust the reference frequency produced by the local oscillator. |
