High spectral purity digital waveform synthesizer

• US 5,495,202 A
• Filed: 06/30/1993
• Issued: 02/27/1996
• Est. Priority Date: 06/30/1993
• Status: Expired due to Term

• Current Assignee: Hughes Electronics Corporation (AT&T, Inc.)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Hsu, Steve I.
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): NGUYEN, TIEP HUU
• Application Number:
  US08/089,066
• Time in Patent Office: 972 Days
• Field of Search: 307/271, 328/14, 328/60, 364/607, 364/608, 364/851, 364/852
• US Class Current: 327/113
• CPC Class Codes: H03B 21/04 using several similar stages
• CPC Class Codes: H03B 2200/0072 Frequency hopping and enabling of rapid frequency changes
• CPC Class Codes: H03B 2200/0088 Reduction of noise

Abstract

A digital waveform synthesizer, using a direct digital synthesizer and a digital frequency divider. The direct digital synthesizer provides a digitally synthesized input frequency signal. An upconverter and frequency divider circuit upconverts and divides the synthesized input frequency signal to provide an divided synthesized frequency signal. An output upconverter circuit is coupled to the upconverter and divider circuit for providing an upconverted output frequency signal. A reference frequency generator is coupled to the direct digital synthesizer, to the upconverter and divider circuit, and to the output upconverter, for providing clock and frequency reference signals thereto. The waveform generator is coupled to the direct digital synthesizer for commanding a desired waveform. The frequency divider is used to improve the inherently poor spurious signal performance of the direct digital synthesizer. The digital waveform synthesizer provides fast switching, flexible and precisely defined frequency output signals. The digital waveform synthesizer may be used with any signal generator that requires high spectral purity and frequency precision, but requires relatively narrow signal bandwidth.

Claims

1. A digital waveform synthesizer comprising:

a direct digital synthesizer for providing a digitally synthesized input frequency signal;

a reference frequency generator for providing a clock signal to the direct digital synthesizer and predetermined frequency reference signals;

an upconverter and divider circuit coupled to the direct digital synthesizer for upconverting and dividing the synthesized input frequency signal to provide a divided synthesized frequency signal, said upconverter and divider circuit comprising;

a mixer having an input coupled to the direct digital synthesizer for receiving the synthesized input frequency signal, and having a second input coupled to the reference signal generator for receiving a first predetermined reference frequency signal;

a bandpass filter coupled to the mixer;

a divide by N divider circuit, where N is a divide number, coupled to the bandpass filter; and

a low pass filter coupled to the divide by N divider circuit;

an output upconverter circuit coupled to the upconverter and divider circuit and to the reference frequency generator for upconverting the divided synthesized frequency signal to provide a desired upconverted synthesized output frequency signal;

a calibration signal generator coupled in parallel with the upconverter and divider circuit; and

switching means having inputs coupled to the calibration signal generator and the upconverter and divider circuit and having an output coupled to the output upconverter circuit for switching therebetween to provide for calibration and variable frequency signal sources.

2. The digital waveform synthesizer of claim 1 which further comprises a waveform generator coupled to the direct digital synthesizer for providing digital commands thereto and for commanding a desired waveform.

3. The digital waveform synthesizer of claim 1 which further comprises at least one additional upconverter and divider circuit coupled between the upconverter and divider circuit and the output upconverter circuit, and that is coupled to the reference frequency generator for receiving at least one additional predetermined frequency reference signal therefrom to provide for additional upconversion and division of the synthesized input frequency signal.

4. The digital waveform synthesizer of claim 2 wherein the waveform generator comprises:

a frequency accumulator adapted to receive frequency modulated ramp slope signals from an external source; and

a control circuit coupled to the frequency accumulator and to the external source for processing input control signals derived from the external source and causing the frequency accumulator to generate linear frequency ramp commands.

5. A digital waveform synthesizer comprising:

a direct digital synthesizer for providing a digitally synthesized input frequency signal;

a reference frequency generator for providing a clock signal to the direct digital synthesizer and predetermined frequency reference signals;

an upconverter and divider circuit coupled to the direct digital synthesizer for upconverting and dividing the synthesized input frequency signal to provide a divided synthesized frequency signal, said upconverter and divider circuit comprising;

a mixer having an input coupled to the direct digital synthesizer for receiving the synthesized input frequency signal, and having a second input coupled to the reference signal generator for receiving a first predetermined reference frequency signal;

a bandpass filter coupled to the mixer;

a divide by N divider circuit, where N is a divide number, coupled to the bandpass filter; and

a low pass filter coupled to the divide by N divider circuit;

a waveform generator coupled to the direct digital synthesizer for providing digital commands thereto and for commanding a desired waveform, wherein the waveform generator comprises;

a frequency accumulator adapted to receive frequency modulated ramp slope signals from an external source, and

a control circuit coupled to the frequency accumulator and to the external source for processing input control signals derived from the external source and causing the frequency accumulator to generate linear frequency ramp commands.