| 摘要 |
A radio receiver comprises an input (14) for a modulated radio frequency signal, a frequency down converter (16) coupled to the input, the frequency down converter including quadrature mixers (32,34) for demodulating a received modulated radio frequency signal using a local oscillator signal. An analogue-to-digital converter (54, 56) is coupled to receive demodulated signals from the mixing means. The analogue-to-digital converter, which may comprise a continuous time sigma delta converter, has an input for a sampling clock frequency (f s). A voltage controlled oscillator (38) provides the local oscillator signal and supplies a frequency divider (60, 94) used to provide the sampling clock frequency. The dividing ratio (1/A) of the frequency divider is variable in response to variations in the strength of an 15 output signal from the digital-to-frequency converter and the variations in the frequency of the sampling clock frequency vary the gain of the analogue-to-frequency converter thereby providing automatic gain control. |
