Method and apparatus for digital frequency synthesis

• US 6,891,420 B2
• Filed: 12/21/2001
• Issued: 05/10/2005
• Est. Priority Date: 12/21/2001
• Status: Active Grant

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Stengel, Robert E., Martin, Frederick L., Juan, Jui-Kuo
• Primary Examiner(s): Nguyen, Simon
• Application Number:
  US10/036,558
• Publication Number:
  US 20030119465A1
• Time in Patent Office: 1,236 Days
• Field of Search: 455/76, 455/183.1, 455/165.1, 455/209, 455/242.1, 455/242.2, 455/243.1, 455/260, 455/550.1, 375/327, 375/354, 375/373, 375/375, 375/376, 327/269, 327/271, 327/272, 327276-277, 327/284, 327/294
• US Class Current: 327/260
• CPC Class Codes: H03L 7/0816 the controlled phase shifter and the frequency- or phase-detection arrangement being connected to a common input
• CPC Class Codes: H03L 7/16 Indirect frequency synthesis, i.e. generating a desired one of a number of predetermined frequencies using a frequency- or phase-locked loop
• CPC Class Codes: H03L 7/22 using more than one loop

Abstract

A digital frequency synthesizer includes one or more reference clocks (104, 1316, 1502A, 1504A, 1506A) optionally coupled through one or more pulse width reducers (106) to one or more main delay lines (108, 702, 1502B, 1504B, 1506B) that include a plurality of output taps (108B-108I, 702B-702E). During at least certain periods of the reference clock (104) a plurality of the output taps are coupled to a common output (130, 1312, 1508), thereby producing an output signal that has a frequency that exceeds a frequency of the one or more reference clocks. The coupling is preferably accomplished by transmission gates (114, 128, 720-724, 1420-1434) that are switched by gating pulses that are received from decoders (148, 150, 1418) via gating signal delay lines (134-146, 704-718, 1404-1416).

Claims

1. A wireless communication device comprising:

a mixer including;

a first input for receiving a first signal that includes coded information;

a second input for receiving a locally generated signal for mixing with the first signal;

a digital frequency synthesizer including;

one or more delay lines including a plurality of output taps;

one or more clock signal sources coupled to the one or more delay lines;

one or more multiplexers including;

a plurality of signal inputs coupled to the plurality of output taps;

a plurality of address inputs; and

a common output coupled to the second input of the mixer; and

a controller including a plurality of control signal outputs coupled to the plurality of address inputs, for causing the one or more multiplexers to couple a plurality of output taps to the common output during a plurality of periods of a clock signal generated by at least one of the one or more clock signal sources.

2. A digital frequency synthesizer comprising:

a clock signal source for outputting a clock signal that is characterized by a clock signal period;

a first delay line including;

a first delay line input coupled to the clock signal source; and

a plurality of first delay line output taps;

a plurality of transmission gates each of which include;

a first signal terminal coupled to one of the plurality of first delay line output taps;

a second signal terminal coupled to a common output; and

a gate control terminal;

a plurality of decoders each of which includes;

one or more decoder address inputs; and

a plurality of decoder outputs;

a plurality of gate signal delay lines each of which is characterized by one of a plurality of delay durations and includes;

an input that is coupled a decoder output of each of the plurality of decoders;

an output coupled to the gate control terminal of one of the plurality transmission gates,

a controller including;

a set of control signal outputs coupled to the one or more decoder address inputs of the plurality of decoders.

3. The digital frequency synthesizer according to claim 2 wherein:

a delay associated with each gate signal delay line is commensurate with a delay that characterizes a tap of the first delay line that is coupled to a transmission gate to which the gate signal delay line is coupled.

4. The digital frequency synthesizer according to claim 2 wherein:

the delay line is characterized by a propagation delay length of about an integer multiple of the clock signal period.

5. The digital frequency synthesizer according to claim 2 wherein:

the plurality of first delay line output taps are spaced by about a fraction of the clock signal period, wherein a denominator of the fraction is indivisible by a numerator of the fraction; and

the first delay line is characterized by a propagation delay length of about the numerator of the fraction times the clock signal period.

6. The digital frequency synthesizer according to claim 2 wherein:

the first delay line further comprises;

a delay control input; and

the digital frequency synthesizer further comprises;

a phase detector including;

a first phase detector input coupled to the first delay line;

a second phase detector input coupled to the clock signal source;

a phase detector output;

a low pass filter including;

an low pass filter input coupled to the phase detector output; and

a low pass filter output coupled to the delay control input.

7. The digital frequency synthesizer according to claim 2 wherein the controller comprises:

a first adder including;

a first summand input for receiving a first control number;

a second summand input;

a first adder output coupled to the second summand input;

an overflow output; and

a first clock input coupled to the clock signal source;

a second adder including;

a second clock input coupled to the overflow output of the first adder;

a third summand input for receiving a second control number;

a fourth summand input;

a second adder output coupled to the fourth summand input wherein the second adder output serves as a subset of the set of control signal outputs of the controller.

8. The digital frequency synthesizer according to claim 7 wherein the controller further comprises:

an overflow signal duration reducer coupled between the overflow output of the first adder and the second clock input.

9. The digital frequency synthesizer according to claim 7 wherein the controller further comprises:

one or more address modifiers, each of which is interposed between the second adder output and the one or more decoder address inputs of one of the plurality of decoders.

10. The digital frequency synthesizer according to claim 9 wherein the one or more address modifiers each comprise:

an address modifier adder for adding approximately an integer multiple of a ratio of a period of a signal to be synthesized and a period of the clock signal to an address output at the second adder output.

11. The digital frequency synthesizer according to claim 10 wherein the one or more address modifiers each comprise:

a selective delayer for determining if an incremented address output by the address modifier adder exceeds a predetermined maximum address and if so delaying the address in reaching the one or more address inputs of one of the plurality of decoders by one period of the reference clock.

12. A method of digitally synthesizing a signal, the method comprising the steps of:

generating a clock signal that includes a plurality of successive clock signal periods;

reducing a pulse width of the clock signal;

coupling the clock signal to a delay line that includes;

an input end;

a plurality of taps including;

a zeroth tap that is located closest to the input end; and

a last tap that is furthest from the input end; and

during at least one clock signal period, selecting and coupling two or more of the plurality of taps to an output.

13. The method according to claim 12 wherein the step of selecting and coupling two or more of the plurality of taps to the output includes the steps of:

during each kth clock signal period selecting a plurality of taps that are spaced from each other by delays that when divided by a period of the clock signal yield remainders that are about equal to integer multiples of a generated signal period.

14. The method according to claim 13 wherein:

a last selected tap selected during each kth clock signal period is spaced from the zeroth tap by a first propagation delay that when divided by the clock signal period yields a first remainder that when subtracted from the clock signal period yields a difference that is less than the generated signal period,

selecting during a successive (k+1)th clock signal period a second selected tap that is spaced from the zeroth tap by second propagation delay that when divided by the clock signal period yields a second remainder that when added to the difference yields a sum that is equal to the generated signal period.

15. The method according to claim 12 wherein the step of coupling one or more of the plurality of taps to the output includes the steps of:

during each kth clock signal period coupling to the output a plurality of taps that are spaced from each by about a generated signal period.

16. The method according to claim 15:

the plurality of taps selected during each kth clock signal period includes;

a first selected tap that is positioned closest, among the plurality of taps, to the zeroth tap; and

a last selected tap that is positioned furthest, among the plurality of taps, from the zeroth tap; and

wherein a first propagation delay time between the zeroth tap and the last selected tap, during each kth clock signal period, when subtracted from the clock signal period yields a difference that when added to a second propagation delay time between the zeroth tap and the first selected tap for each successive (k+1)th clock signal period is equal to about the generated signal period.