| 摘要 |
<p>A wideband fast-hopping receiver front-end uses direct digital synthesis (DDS) to provide quadrature LO signals (108, 110) to the front-end's mixers (100, 102). A DDS circuit (132) stores multiple digital word sequences which represent desired waveforms, and outputs desired sequence pairs to a pair of DACs (134, 136) in response to a closk signal and a command signal. The DACs convert the sequences to analog signals, which are filtered and squared as necessary to provide quadrature LO signals to the mixers. Frequency hopping is accomplished by changing the command signal, which causes a different pair of sequences to be output and the frequency of the LO signals provided to the mixers to be changed. Active image rejection is combined with DDS LO generation to provide faster frequency hopping. The front-end is combined with an ADC (180) and a communications signal processor (184) to provide a complete system, all of which can be integrated together on a common substrate.</p> |
