Digital sweep generator

• US 4,943,779 A
• Filed: 05/19/1988
• Issued: 07/24/1990
• Est. Priority Date: 05/19/1988
• Status: Expired due to Fees

• Current Assignee: Worcester Polytechnic Institute
• Original Assignee: Worcester Polytechnic Institute
• Inventors: Pedersen, Peder C., Green, Thomas J. Jr.
• Primary Examiner(s): Callahan, Timothy P.
• Application Number:
  US07/195,790
• Time in Patent Office: 796 Days
• Field of Search: 307/228, 307/529, 307/260, 307/271, 328/14, 328/181, 328/185, 328/15, 328/16, 328/27
• US Class Current: 327/106
• CPC Class Codes: H03B 2200/0092 Measures to linearise or reduce distortion of oscillator characteristics
• CPC Class Codes: H03B 23/00 Generation of oscillations periodically swept over a predetermined frequency range angle-modulating circuits in general H03C3/00

Abstract

A digital sweep generator includes a counter which receives a clock signal to generate a frequency output and an accumulator which sums the outputs of the counter at each clock. The value held by the accumulator is a quadratic function of time which is used as a phase representation to address a wave generator PROM. The PROM may be selectively coupled to different ranges of accumulator output to set the sweep rate.

Claims

1. A digital sweep generator for synthesizing a sweep signal of a predetermined periodic waveform swept through a range of frequencies, the generator comprising:

a counter for counting clock signals and providing a clock signal count;

means for setting the count from the counter to a value representative of an initial frequency of the sweep signal;

means for stopping the sweep signal after the clock signal count reaches a value representative of a predetermined stop frequency of the sweep signal;

a digital accumulator which sums successive clock signal counts from the counter for accumulating a count of clock signals as phase angle values of a sweep signal output as any of different selected sets of multiple bits;

a look-up table memory for receiving a selected set of multiple bits output from the accumulator and having stored therein values of a single cycle of the periodic waveform as a function of phase angle within a single cycle and responding to different selected sets of multiple bits output from the accumulator to vary sweep frequency of the sweep signal; and

a digital-to-analog converter coupled to receive and to convert to analog form stored values from the memory through successive cycles of the waveform.

2. A sweep generator as claimed in claim 1 further comprising means for setting the accumulator to an initial phase.

3. A sweep generator as claimed in claim 1 in combination with one or more like sweep generators, the sweep generators being responsive to a common clock signal for providing at least two synchronized sweep signals.

4. A sweep generator as claimed in claim 1 wherein the values stored in the look-up table memory are of a sinusoidal function.

5. A method of synthesizing a periodic waveform swept through a range of frequencies, the method comprising:

selecting an initial count of clock signals to set an initial frequency and selecting an initial accumulated sum of counts of clock signals to set an initial phase;

digitally generating a multibit phase signal by counting clock signals and accumulating sums of counts of the clock signals, any of selected sets of bits of which are digital representations of phase angle of successive cycles of the periodic waveform swept through a range of frequencies;

selecting frequency of the clock signals in combination with selecting one of the selected sets of bits, the bits of the set being less than all bits of the multibit phase signal, to represent a single cycle of the periodic waveform, sweep frequency of the waveform being determined by the selected set of bits;

digitally generating successive cycles of a sweep signal by means of a single cycle waveform generator responsive to the selected set of bits; and

stopping the sweep signal when the count reaches a value representative of a predetermined stop frequency.

6. A method as claimed in claim 5 wherein the step of generating the waveform comprises addressing a look-up table memory.

7. A sweep generator for synthesizing a sweep signal of predetermined periodic waveform sweep through a range of frequencies, the generator comprising:

a counter for counting clock signals to provide counts as indications of frequency;

a digital accumulator for accumulating counts of clock signals to generate phase angle values of a sweep signal;

a look-up table memory having stored therein values of a single cycle of the periodic waveform as a function of phase angle within a single cycle and coupled to receive phase angle values output from the accumulator;

a digital-to-analog converter coupled to receive and to convert to analog form stored values from the memory through successive cycles of the waveform; and

means responsive to the count from the counter for stopping synthesis of the sweep signal when the count of clock signals indicates a predetermined stop frequency.

8. A method of synthesizing a periodic waveform swept through a range of frequencies, the method comprising:

counting clock signals to provide an indication of frequency;

accumulating sums of counts of clock signals to provide a digital representation of phase angle of successive cycles of the periodic waveform swept through a range of frequencies;

generating successive cycles of a sweep signal by means of a single cycle waveform generator responsive to the digital representations of phase angle; and

stopping the sweep signal when the count of clock signals reaches a predetermined stop frequency.

9. A sweep generator system for synthesizing sweep signals of predetermined periodic waveforms swept through respective ranges of frequencies, the system comprising:

a master clock for generating clock signals; and

a plurality of sweep generators, each sweep generator comprising;

a counter for counting clock signals from the master clock;

an accumulator for accumulating counts of clock signals as phase angle values of a sweep signal;

means for setting the phase angle value from the accumulator to an initial phase angle value;

means for setting the count from the counter to a value representative of an initial frequency of the sweep signal;

a waveform generator for generating a cycle of a predetermined waveform as a function of phase angle and responsive to the phase angle values generated by the accumulator to generate successive cycles of the sweep signal; and

means responsive to the count from the counter for stopping synthesis of the sweep signal after the clock signal count reaches a value representative of a predetermined stop frequency of the sweep signal.

10. A system as claimed in claim 9 wherein the accumulator generates a multibit phase signal, selected bits of which are representative of the phase angle values, and the waveform generator is adapted to be coupled to respond to different selected bits of the phase signal.