Patent ID: 6693980
Filing Date: 2004-02-17
Classification: H03D

Abstract:
A wideband fast-hopping receiver front-end, comprising:a first mixer which receives a radio frequency (RF) signal at a first input, a first wideband local oscillator (LO) signal at a second input, and which produces an output which includes components derived from the sum of its two input signals and from the difference of its two input signals, a second mixer which receives said RF signal at a first input, a second wideband LO signal at a second input, and which produces an output which includes components derived from the sum of its two input signals and from the difference of its two input signals, at least one intermediate frequency (IF) phase shift circuit connected in series with at least one of said mixer outputs to introduce a phase difference of 90 degrees between said mixer outputs, a summing circuit which sums said mixer outputs having a phase difference of 90 degrees between them to provide an intermediate frequency (IF) output, and a wideband I/Q LO generating circuit connected to provide said first and second wideband LO signals to said mixers and to enable wideband image rejection over a wide range of RF signal frequencies, said wideband I/Q LO generating circuit comprising: a direct digital synthesis (DDS) circuit which stores multiple pairs of digital word sequences, receives a clock signal and a command signal at first and second inputs, respectively, and selects one of said stored digital word sequence pairs to be produced at first and second outputs in response to said command and clock signals, each of said stored digital word sequence pairs representing first and second periodic waveforms having a particular frequency and a phase difference of 90 degrees between them, a first digital-to-analog converter (DAC) which receives said first output from said DDS at an input and which produces said first periodic waveform at an output, said first periodic waveform being said first wideband LO signal, and a second digital-to-analog converter (DAC) which receives said second output from said DDS at an input and which produces said second periodic waveform at an output, said second periodic waveform being said second wideband LO signal.