| 摘要 |
<p>This invention relates to apparatus and methods for radio receivers, in particular low (IF) frequency receivers. Embodiments of the invention are particularly suitable for digital audio broadcast receivers. A low-IF radio receiver circuit, the circuit comprising: an rf input for a received rf signal; a first local oscillator having a quadrature output to provide a quadrature first local oscillator signal at a first frequency; a quadrature first mixer coupled to said rf input and to said quadrature-output of said first local-oscillator and having a quadrature first mixer output, and said first mixer and said first local oscillator being configured to provide quadrature mixing of said quadrature first local oscillator signal and said received rf signal to downconvert said received rf signal to a first quadrature IF Signal at a first IF frequency; a bandpass filter coupled to said quadrature first mixer output and having a filtered output to provide a bandpass filtered first IF signal; a second local oscillator having a second local oscillator output to provide a second local oscillator signal at a second frequency; a second mixer coupled to said filtered output of said bandpass filter and to said second local oscillator and having a second mixer output, said second mixer and said second local oscillator being configured to provide mixing of said second local oscillator signal and said bandpass filtered first IF signal to up-convert said bandpass filtered first IF signal to a second IF signal at a second IF frequency, wherein said second IF frequency is greater than said first IF frequency; and an output coupled to said second mixer output to provide an output signal from said second IF signal.</p> |
