Delay locked loop synthesizer with multiple outputs and digital modulation

• US 7,162,000 B2
• Filed: 01/16/2002
• Issued: 01/09/2007
• Est. Priority Date: 01/16/2002
• Status: Active Grant

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Bockelman, David E., Stengel, Robert E., Heck, Joseph P.
• Primary Examiner(s): Kim; Kevin
• Assistant Examiner(s): Wong; Linda
• Application Number:
  US10/050,233
• Publication Number:
  US 20030152181A1
• Time in Patent Office: 1,819 Days
• Field of Search: 708/316, 375/371, 375/376, 375/322, 375/271, 375/373, 375/327, 375/354, 375/375, 327/158, 327/146, 327/155, 327/152, 327/156, 327/161, 327/183, 327/182, 327/269, 327/141, 327147-150, 327/159, 370/503, 370/516, 370/517, 370/518, 370/215, 370/483
• US Class Current: 375/373
• CPC Class Codes: H03K 2005/00019 Variable delay
• CPC Class Codes: H03K 7/04 Position modulation, i.e. PPM
• CPC Class Codes: H03L 7/0814 the phase shifting device being digitally controlled
• 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: H04L 27/0008 arrangements for allowing a transmitter or receiver to use more than one type of modulation negotiating modulation type for two-way transmission paths H04L5/1453

Abstract

A delay locked loop circuit (200) in which multiple outputs are produced. A single delay line (24) is shared among multiple tap selection circuits (256A, 265B, 265C). Fixed phase shifts (412) can be introduced between multiple outputs. A modulating signal can be used in the tap selection processing to produce digital amplitude, frequency and/or phase modulation.

Claims

1. A circuit, comprising:

a delay locked loop having a delay line with a plurality of tap outputs;

a first tap selection circuit that produces a first set of tap addresses to select a first set of the plurality of tap outputs from the delay line according to a first timing to produce a first output signal;

a second tap selection circuit that produces a second set of tap addresses to select a second set of the plurality of tap outputs from the delay line according to a second timing to produce a second output signal;

a modulator combining the first and second output signals to produce a modulated output signal; and

wherein the modulator frequency-modulates the first output signal with the second output signal.

2. A circuit, comprising:

a delay locked loop having a delay line with a plurality of tap outputs;

a first tap selection circuit that produces a first set of tap addresses to select a first set of the plurality of tap outputs from the delay line according to a first timing to produce a first output signal;

a second tap selection circuit that produces a second set of tap addresses to select a second set of the plurality of tap outputs from the delay line according to a second timing to produce a second output signal;

a modulator combining the first and second output signals to produce a modulated output signal; and

wherein the modulator phase-modulates the first output signal with the second output signal.

3. A circuit, comprising:

a delay locked loop having a delay line with a plurality of tap outputs;

a first tap selection circuit that produces a first set of tap addresses to select a first set of the plurality of tap outputs from the delay line according to a first timing to produce a first output signal;

a second tap selection circuit that produces a second set of tap addresses to select a second set of the plurality of tap outputs from the delay line according to a second timing to produce a second output signal;

a modulator combining the first and second output signals to produce a modulated output signal; and

wherein the modulator amplitude-modulates the first output signal with the second output signal.

4. A circuit, comprising:

a delay locked loop having a delay line with a plurality of tap outputs;

a first tap selection circuit that produces a first set of tap addresses to select a first set of the plurality of tap outputs from the delay line according to a first timing to produce a first output signal;

a second tap selection circuit that produces a second set of tap addresses to select a second set of the plurality of tap outputs from the delay line according to a second timing to produce a second output signal;

a tap selection processor that selects the first set of the plurality of tap outputs from the delay line according to the first timing, and selects the second set of the plurality of tap outputs from the delay line according to the second timing, the tap selection processor comprising;

a frequency accumulator receiving an integer part K of K.C where K.C=F_out/F_ref, where F_out is a desired output frequency and F_ref is a reference clock frequency, and wherein the frequency accumulator is clocked by F_ref; and

a phase accumulator that receives the fractional part C of K.C, wherein the phase accumulator is clocked by an overflow of the frequency accumulator, and wherein the frequency accumulator produces the first set of the plurality of tap output addresses as an output thereof;

a first demultiplexer responsive to the tap selection processor to selectively route the selected first set of the plurality of tap outputs to a common node to produce the first output signal; and

a second demultiplexer responsive to the tap selection processor to selectively route the selected second set of the plurality of selected tap outputs to another common node to produce the second output signal.

5. A circuit, comprising:

a delay locked loop having a delay line with a plurality of tap outputs;

a first tap selection circuit that produces a first set of tap addresses to select a first set of the plurality of tap outputs from the delay line according to a first timing to produce a first output signal, the first tap selection circuit further comprising;

a first tap selection processor that selects the first set of the plurality of tap outputs from the delay line according to the first timing; and

a first demultiplexer responsive to the first tap selection processor to selectively route the selected first set of tap outputs to a common node to produce the first output signal;

a second tap selection circuit that produces a second set of tap addresses to select a second set of the plurality of tap outputs from the delay line according to a second timing to produce a second output signal, the second tap selection circuit further comprising;

a second tap selection processor that selects the second set of the plurality of tap outputs from the delay line according to the second timing; and

a second demultiplexer responsive to the second tap selection processor to selectively route the selected second set of tap outputs to another common node to produce the second output signal;

and wherein the first tap selection processor comprises;

a frequency accumulator receiving an integer part K of K.C where K.C=F_out/F_ref, where F_out is a desired output frequency and F_ref is a reference clock frequency, and wherein the frequency accumulator is clocked by F_ref; and

a phase accumulator that receives the fractional part C of K.C, wherein the phase accumulator is clocked by an overflow of the frequency accumulator, and wherein the frequency accumulator produces the first set of the plurality of tap output addresses as an output thereof.

6. The apparatus according to claim 5, wherein the second tap selection processor comprises a phase offset adder receiving the first set of the plurality of tap outputs as a first input and a normalized phase shift as a second input thereto and producing the second set of the plurality of tap output addresses as an output thereof, and wherein the phase offset adder is clocked by the overflow of the frequency accumulator.

7. A circuit for producing two output signals having frequency F_out and differing by a phase shift, comprising:

a delay locked loop having a plurality of addressable tap outputs;

a tap selection circuit that selects a first sequence of tap addresses C_ja from the addressable tap outputs;

an adder that adds a normalized phase shift component Φ

=α

/ (2 π

) (α

=a desired phase shift in radians) to the first sequence of tap addresses C_ja to produce a second sequence of tap addresses C_jb, where C is the fractional part of K.C in K.C=F_out/F_ref, and F_ref being a reference clock frequency; and

a first multiplexer and a second multiplexer, wherein the first sequence of tap addresses C_ja are applied to the first multiplexer to produce a first output signal F_outa, and wherein the second sequence of tap addresses C_jb are applied to the second multiplexer to produce a second output signal F_outb, and wherein F_outa differs from F_outb by the desired phase shift.

8. The apparatus according to claim 7, wherein the desired phase shift comprises ±

90 degrees.

9. The apparatus according to claim 7, wherein the desired phase shift component Φ

comprises a time varying phase shift component.

10. A circuit for producing two output signals differing by a phase shift, comprising:

a delay locked loop having a plurality of addressable delay line tap outputs, the delay locked loop synthesizing the output signals at a frequency F_out, with K.C=F_out/F_ref, and F_ref being a reference clock frequency;

a tap selection circuit that selects a sequence of tap addresses C_ja from the plurality of addressable delay line tap outputs;

a first multiplexer, wherein the sequence of tap addresses C_ja are applied to a plurality of inputs of the first multiplexer to produce a first output signal F_outa;

a second multiplexer, wherein the sequence of tap addresses C_ja are added to a delay factor α

/(2π

) where α

is a desired phase shift in radians and applied to a plurality of inputs of the second multiplexer to produce a second output signal F_outb; and

wherein the first and second multiplexers each comprise N;

1 multiplexers having N inputs.

11. The apparatus according to claim 10, wherein α

corresponds to a fixed phase shift.

12. The apparatus according to claim 10, wherein the α

corresponds to ±

90 degrees.

13. The apparatus according to claim 10, wherein the α

comprises a time varying phase shift.

14. A digital frequency modulator, comprising:

a delay locked loop having a delay line with a plurality of tap outputs;

a tap selection processor that selects, from the delay line with the plurality of tap outputs, a sequence of time varying tap addresses C_j(t) that vary in time in accordance with a modulating signal m(t); and

a multiplexer circuit, and wherein the time varying tap addresses C_j(t) are applied to the multiplexer circuit to select a time varying sequence of tap outputs as a frequency modulated output signal F_out(t) wherein the tap selection processor comprises an integrator that integrates the modulating signal m(t) and an adder that adds the integrated modulating signal m(t) to a selected sequence of tap addresses C_j to produce C_j(t).

15. The apparatus according to claim 14, wherein the time varying tap addresses C_j(t) are further selected to amplitude modulate the output signal F_out(t) in accordance with the modulating signal m(t).

16. The apparatus according to claim 14, wherein the time varying tap addresses C(t) are further selected to phase modulate the output signal F_out(t) in accordance with the modulating signal m(t).

17. The apparatus according to claim 14, wherein the modulating signal m(t) comprises an analog signal.

18. The apparatus according to claim 14, wherein the modulating signal m(t) comprises a data signal.

19. A digital amplitude modulator, comprising:

a delay locked loop having a delay line with a plurality of tap outputs;

a tap selection processor that selects, from the delay line with the plurality of tap outputs, a sequence of time varying tap addresses C_j(t) that vary in time in accordance with a modulating signal m(t);

a multiplexer circuit, and wherein the time varying tap addresses C_j(t) are applied to the multiplexer circuit to select a time varying sequence of tap outputs as an output signal F_out(t); and

wherein the tap selection processor comprises;

a first adder that adds the modulating signal m(t) to a selected sequence of tap addresses C_ja to produce a first sequence of time varying tap addresses C_jb(t);

a second adder that subtracts the modulating signal m(t) from the selected sequence of tap addresses C_ja to produce a second sequence of time varying tap addresses C_jc(t); and

wherein C_j(t) comprises C_jb(t) and C_jc(t); and

wherein the multiplexer circuit comprises;

a first multiplexer receiving the first sequence of time varying tap addresses C_jb(t) to produce a first output signal V₁(t); and

a second multiplexer receiving the second sequence of time varying tap addresses C_jc(t) to produce a second output signal V₂(t);

and further comprising;

a summation circuit that adds V₁(t) to V₂(t) to obtain an amplitude modulated output signal V(t).

20. The apparatus according to claim 19, wherein the adding circuit comprises an analog summation circuit.

21. The apparatus according to claim 20, wherein the summation circuit comprises a three state analog summation circuit.

22. The apparatus according to claim 21, wherein the three state analog summation circuit comprises a NAND gate and a NOR gate, each receiving V1(t) and V2(t) and producing first and second outputs therefrom;

and a first and a second transistor connected in series and driven by the first and second outputs respectively to produce a three state output at a node coupling the first transistor with the second transistor.

23. The apparatus according to claim 19, wherein the time varying tap addresses C_j(t) are further selected to frequency modulate the output signal F_out(t) in accordance with the modulating signal m(t).

24. The apparatus according to claim 19, wherein the time varying tap addresses C(t) are further selected to phase modulate the output signal F_out(t) in accordance with the modulating signal m(t).

25. The apparatus according to claim 19, wherein the modulating signal m(t) comprises an analog signal.

26. The apparatus according to claim 19, wherein the modulating signal m(t) comprises a data signal.

27. A method of producing multiple output frequencies using a delay locked loop having a delay line with a plurality of tap outputs, comprising:

selecting a first sequence of the tap outputs from the delay line having the plurality of tap outputs according to a first timing to produce a first output signal F_out1;

selecting a second sequence of the tap outputs from the delay line having the plurality of tap outputs according to a second timing to produce a second output signal F_out2.; and

applying addresses of the first sequence of tap outputs to a first multiplexer to perform selecting the first sequence of tap outputs; and

applying addresses of the second sequence of tap outputs to a second multiplexer to perform selecting-the second sequence of tap outputs; and

modulating the first sequence of tap outputs with the second sequence of tap outputs.

28. A method of producing two output signals differing by a phase shift in a delay locked loop circuit having a delay line with a plurality of addressable tap outputs, comprising:

selecting a first sequence of tap addresses C_ja;

adding a phase shift component Φ

to the first sequence of tap addresses C_ja to produce a second sequence of tap addresses C_jb; and

applying the first sequence of tap addresses C_ja to a first multiplexer to produce a first output signal F_outa; and

applying the second sequence of tap addresses C_jb to a second multiplexer to produce a second output signal F_outb, and wherein F_outa differs from F_outb by a phase shift related to Φ

.

29. The method according to claim 28, wherein the phase shift comprises ±

90 degrees.

30. The method according to claim 28, wherein the phase shift component Φ

comprises a time varying phase shift component.

31. A method of producing two output signals differing by a phase shift using a delay locked loop having a plurality of addressable delay line tap outputs, comprising:

selecting a sequence of tap addresses C_ja from the delay locked loop having a delay line providing the plurality of addressable delay line tap outputs;

applying the sequence of tap addresses C_ja to a plurality of inputs of a first multiplexer to produce a first output signal F_outa; and

applying the sequence of tap addresses C_ja to a plurality of inputs of a second multiplexer to produce a second output signal F_outb;

wherein F_out1 differs from F_out2 by the phase shift, and wherein the phase shift is determined by a constant difference in address location selected by the sequence of tap addresses C_ja between the first and second multiplexers.

32. The method according to claim 31, wherein the first and second multiplexers are connected to the tap outputs in a manner such that a tap address from the sequence of tap addresses selects an input corresponding to tap number L of the first multiplexer and corresponding to tap number L+Φ

in the second multiplexer, where Φ

is a phase shift normalized to a length of the delay line.

33. The method according to claim 32, wherein the sequence of tap addresses C_ja is applied to the second multiplexer through a delay element.

34. The apparatus according to claim 31, wherein the phase shift corresponds to ±

90 degrees.

35. The apparatus according to claim 31, wherein the phase shift comprises a time varying phase shift.

36. A method of providing digital frequency modulation in a delay locked loop circuit having a delay line with a plurality of tap outputs, comprising:

selecting a sequence of time varying tap addresses C_j(t) that vary in time in accordance with a modulating signal m(t), wherein the selecting comprises;

integrating the modulating signal m(t); and

adding the integrated modulating signal m(t) to a selected sequence of tap addresses C_j to produce C_j(t); and

applying the time varying tap addresses C_j(t) to a multiplexer circuit to select a time varying sequence of tap outputs as a frequency modulated output signal F_out(t).

37. A method of providing digital amplitude modulation in a delay locked loop circuit having a delay line with a plurality of tap outputs, comprising:

selecting a sequence of time varying tap addresses C_j(t) that vary in time in accordance with a modulating signal m(t), wherein the selecting comprises;

adding the modulating signal m(t) to a selected sequence of tap addresses C_ja to produce a first sequence of time varying tap addresses C_jb(t); and

subtracting the modulating signal m(t) from the selected sequence of tap addresses C_ja to produce a second sequence of time varying tap addresses C_jc(t),

wherein C_j(t) comprises C_jb(t) and C_jc(t); and

applying the time varying tap addresses C_j(t) to a multiplexer circuit to select a time varying sequence of tap outputs as an amplitude modulated output signal F_out(t).

38. The method according to claim 37, and wherein the applying comprises:

applying the first sequence of time varying tap addresses C_jb(t) to a first multiplexer to produce a first output signal V₁(t); and

applying the second sequence of time varying tap addresses C_jc(t) to a second multiplexer produce a second output signal V₂(t).

39. The method according to claim 38, further comprising adding V₁(t) to V₂(t) to obtain an amplitude modulated output signal V(t).

40. The method according to claim 39, wherein the adding is carried out in an analog summation circuit.

41. The method according to claim 40, wherein the analog summation circuit comprises a three state analog summation circuit.

42. A method of selecting delay line taps to produce an output signal from a delay locked loop, comprising:

computing an tap address P.Q where P is an integer part and Q is a fractional part; and

selecting a delay line tap address of P during a portion of an operational cycle and of P+1 during a remainder of the operational cycle, with the regularity of selection of P and P+1 determined by an algorithm that establishes an average value of the tap address as approximately P.Q.

43. The method according to claim 42, wherein the algorithm selects the value of P for 1-0.Q operational cycles and selects the value of P+1 for 0.Q operational cycles.