Direct frequency synthesizer

• US 4,791,377 A
• Filed: 10/20/1987
• Issued: 12/13/1988
• Est. Priority Date: 10/20/1987
• Status: Expired due to Fees

• Current Assignee: General Dynamics Government Systems Corporation (General Dynamics Corporation)
• Original Assignee: GTE Government Systems Corporation (General Dynamics Corporation)
• Inventors: Campbell, James T., Gundel, Carl H., Grandfield, John, Shillue, William
• Primary Examiner(s): Miller, Stanley D.
• Assistant Examiner(s): ROSEEN, RICHARD R
• Application Number:
  US07/110,396
• Time in Patent Office: 420 Days
• Field of Search: 328/14, 328/15, 328/27, 328/29, 328/25, 328/30, 328/109, 331/39, 331/40
• US Class Current: 327/105
• CPC Class Codes: H03B 21/025 by repeated mixing in combination with division of frequency only
• CPC Class Codes: H03B 21/04 using several similar stages
• CPC Class Codes: H03B 2200/0072 Frequency hopping and enabling of rapid frequency changes

Abstract

A frequency synthesizer has in series a digital synthesizer, mix and divide circuits, and a mix only circuit. Each mix and divide circuit includes a mixer having an IF input, a LO input and a RF output, a filter, and a frequency divider. A segment of a digital word selects a tone from a tone generator and also selects a passband of the filter. The selected tone is coupled to the LO input of the mixer. The frequency divider divides the filtered RF output of the mixer. The mix only circuit is at the output of the last of the series connected mix and divide circuits. The mix only circuit is similar to a mix and divide circuit, but does not have a frequency divider. The digital synthesizer provides a signal to the input of the first of the series connected mix and divide circuits, the frequency of which corresponds to a segment of a digital word. The filter is preferably a voltage tunable bandpass filter.

Claims

1. A frequency synthesizer comprising:

a. tone generating means for providing a plurality of tones;

b. a plurality of series connected mix and divide circuits, including a first and a last mix and divide circuit, each mix and divide circuit including a mixer having an IF input, an LO input and a RF output, filter means for filtering the RF output of said mixer with a selectable passband;

means for selecting a tone from said tone generating means and selecting a passband of said filter means in response to a segment of a digital word;

means for coupling the selected tone to the IF input of said mixer, and frequency divider means for dividing the filtered RF output of said mixer;

c. a mix only circuit at the output of the last of said series connected mix and divide circuits, said mix only circuit including a mixer having an IF input, a LO input and a RF output, filter means for filtering the RF output of said mixer with a selectable passband, means for selecting a tone from said tone generating means and selecting a passband of said filter means in response to a segment of a digital word;

means for coupling the selected tone to the IF input of said mixer, and

d. a digital synthesizer for providing a signal to the input of the first of said series connected mix and divide circuits, the frequency of said signal corresponding to a segment of a digital word.

2. The frequency synthesizer of claim 1 wherein said filter means is a voltage tunable bandpass filter.

3. A frequency synthesizer comprising:

a. tone generating means for providing a plurality of tones;

b. a plurality of series connected mix and divide circuits including a first and last mix and divide circuit, each mix and divide circuit including a mixer having an IF input, a LO input and a RF output, filter means for filtering the RF output of said mixer with a selectable passband;

means for selecting a tone from said tone generating means and selecting a passband of said filter means in response to a segment of a digital word;

means for coupling the selected tone to the IF input of said mixer; and

frequency divider means for dividing the filtered RF output of said mixer;

c. a mix only circuit at the output of the last of said series connected mix and divide circuits;

said mix only circuit including a mixer having an IF input, a LO input and a RF output, a voltage tunable bandpass filter for filtering the RF output of said mixer with a selectable passband, means for selecting a tone from said tone generating means and selecting a passband of said voltage tunable bandpass filter in response to a segment of a digital word, means for coupling the selected tone to the IF input of said mixer; and

d. a signal source for providing a signal to the input of said series connected mix and divide circuits, the frequency of said signal corresponding to a segment of a digital word.