Rapid frequency synthesizer apparatus and method

• US 4,704,585 A
• Filed: 08/08/1986
• Issued: 11/03/1987
• Est. Priority Date: 08/08/1986
• Status: Expired due to Term

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Lind, Harold V.
• Primary Examiner(s): Grimm, Siegfried H.
• Application Number:
  US06/894,404
• Time in Patent Office: 452 Days
• Field of Search: 331/1 A, 331/16, 331/17, 331/25, 331/14, 375/1, 375/2.2, 375/48, 375/65
• US Class Current: 331/114
• CPC Class Codes: H03L 7/148 said digital means comprising a counter or a divider
• CPC Class Codes: H03L 7/181 a numerical count result being used for locking the loop, the counter counting during fixed time intervals H03L7/1806 takes precedence

Abstract

Rapid frequency synthesizer apparatus, particularly for use in high speed frequency hooping systems, includes a voltage controlled oscillator (VCO) and a memory in which are stored digital control voltage commands corresponding to the various frequencies to be synthesized by the VCO. A controller, responsive to channel selection commands, addresses the memory and causes the corresponding digital control voltage command to be generated. A digital-to-analog converter receives the digital control voltage command and converts it to an analog control voltage signal which is fed to the VCO. The resulting VCO output signal, at frequency, f_out, is compared in a frequency counter with a reference frequency f_R. The controller controls operation of the frequency counter so that a difference between the actual synthesized frequency and the programmed frequency is determined. Responsive to this difference, the controller causes the addressed control voltage command to be modified in a manner designed to reduce the difference the next time the same programmed frequency is selected. A corresponding method for providing rapid frequency synthesis is described.

Claims

1. Rapid frequency synthesizer apparatus which comprises:

(a) a controllable oscillator;

(b) memory means for storing a plurality of different oscillator control commands corresponding to a like plurality of different programmed frequencies to be synthesized by said oscillator;

(c) selecting means enabling the external selecting among said programmed frequencies;

(d) control means responsive to the external selecting of any one of said programmed frequencies for internally selecting the corresponding one of the oscillator control commands stored in the memory means and for applying said selected oscillator control command to said oscillator,

said oscillator being responsive to said selected oscillator control command provided thereto for synthesizing a present actual output frequency corresponding to the selected programmed frequency;

(e) means for comparing said present actual output frequency synthesized with said corresponding selected programmed frequency and for determining a present error difference therebetween; and

(f) means responsive to said present error difference for modifying the selected oscillator control command stored in the memory means in a manner designed to reduce a corresponding error difference the next time the same programmed frequency is selected without changing said present error difference.

2. The frequency synthesizer apparatus as claimed in claim 1 wherein said oscillator is a voltage controlled oscillator.

3. The frequency synthesizer apparatus as claimed in claim 2 wherein said oscillator control commands comprise control voltage commands.

4. The frequency synthesizer apparatus as claimed in claim 3 wherein said control voltage commands are stored in the memory means as digital words and including digital-to-analog converting means for converting said digital words into analog oscillator control voltages.

5. Rapid frequency synthesizer apparatus which comprises:

(a) a voltage controlled oscillator;

(b) memory means for storing a plurality of different oscillator control voltage commands corresponding to a like plurality of different programmed frequencies to be synthesized by the voltage controlled oscillator;

(c) selecting means enabling the external selecting among said programmed frequencies;

(d) control means responsive to the external selecting of any one of said programmed frequencies for internally selecting the corresponding one of the oscillator control voltage commands stored in the memory means and for applying said selected control voltage command to said voltage controlled oscillator,

said voltage controlled oscillator being responsive to said selected control voltage command for synthesizing a present actual output frequency corresponding to the selected programmed frequency;

(e) means for comparing said present actual output frequency with said corresponding selected programmed frequency and for determining a present error difference therebetween; and

(f) means responsive to said present error difference for modifying the selected control voltage command stored in the memory means in a manner designed to reduce a corresponding error difference the next time the same programmed frequency is selected without changing said present error difference.

6. The frequency synthesizer apparatus as claimed in claim 5 wherein said control voltage commands are stored in the memory means in digital format and including digital-to-analog converting means for converting the control voltage commands from the digital format to analog oscillator control voltages.

7. Rapid frequency synthesizer apparatus which comprises:

(a) a voltage controlled oscillator;

(b) memory means for storing, in digital format, a plurality of different oscillator control voltage commands corresponding to a like plurality of different programmed frequencies to be synthesized by said voltage controlled oscillator;

(c) selecting means enabling the external selecting among said programmed frequencies;

(d) control means responsive to the external selecting of any one of the programmed frequencies for internally selecting the corresponding one of the stored control voltage commands;

(e) digital-to-analog-converting means connected for receiving said selected control voltage commands from the memory means and for applying, in response thereto, a corresponding analog control voltage to the oscillator,

said oscillator being responsive to said corresponding analog control voltage for synthesizing a present actual output frequency corresponding to the selected programmed frequency;

(f) means for sampling the present actual output frequency of the voltage controlled oscillator, for comparing said present actual output frequency with said selected programmed frequency and for providing a present error difference between said present actual and programmed frequencies; and

(g) means responsive to said present error difference for modifying the selected control voltage command stored in the memory means in a manner designed to reduce a corresponding error difference the next time the same programmed frequency is selected without changing said present error difference.

8. A method for rapid frequency synthesizing which comprises:

(a) storing in a memory a plurality of different oscillator control commands corresponding to a like plurality of different programmed frequencies to be synthesized;

(b) selecting a particular one of the programmed frequencies to be synthesized and thereby also selecting a corresponding particular one of the stored oscillator control commands;

(c) applying said selected oscillator control command to a frequency synthesizing oscillator to cause said oscillator to provide a present actual output frequency;

(d) comparing the present actual output frequency of the oscillator to the selected one of the programmed frequencies and determining a present error difference therebetween; and

(e) modifying the corresponding particular one of the stored oscillator control commands in response to said present error difference in a manner designed to reduce a corresponding error difference the next time said particular one of the programmed frequencies is to be provided without changing said present error difference.

9. The method as claimed in claim 8 wherein the oscillator voltage commands are stored in digital form in the memory and wherein the oscillator is responsive to analog control commands and including the step of converting the selected one of the oscillator control commands to a corresponding analog control command.

10. The method as claimed in claim 8 wherein the oscillator is a voltage controlled oscillator and wherein the oscillator control commands are voltage commands.

11. A method for rapid frequency synthesizing which comprises:

(a) storing in a random access memory, in digital form, a plurality of different control voltage commands corresponding to a like plurality of different programmed frequencies to be synthesized;

(b) selecting a particular one of the programmed frequencies to be synthesized and thereby also selecting a corresponding one of the stored control voltage commands;

(c) extracting from the memory said selected one of the digital control voltage commands and converting said command to a corresponding analog voltage command;

(d) applying said corresponding analog voltage command to a voltage controlled oscillator to cause the oscillator to synthesize a corresponding present actual frequency;

(d) comparing the present actual synthesized frequency with the selected frequency and determining a present error difference therebetween; and

(e) modifying, in response to said present error difference, the selected one of the control voltage commands stored in the memory in a manner designed to reduce a corresponding error difference the next time said particular one of the programmed frequencies is to be provided without changing said present error difference.