| 摘要 |
<p>A frequency synthesiser comprises a direct digital frequency synthesiser (DDFS) 11, which provides in phase and quadrature sinewave signals at a preset frequency from DACs 12 and 13 respectively, and a balanced mixer 2. The balanced mixer 2 provides an output signal having a carrier frequency twice that provided by DDFS I and reduced levels of spurious signals. A signal having a desired frequency is generated by controlling DDFS 1 to generate sinewave output signals at half the desired frequency. The reduced levels of spurious signals obtained by the arrangement allows improved signals for use in, for example, local oscillator applications. <IMAGE></p> |
