Methods and apparatus for modulating, demodulating and amplifying

• US 5,939,951 A
• Filed: 11/24/1997
• Issued: 08/17/1999
• Est. Priority Date: 05/25/1995
• Status: Expired due to Fees

• Current Assignee: BTG International Limited (Boston Scientific Corporation)
• Original Assignee: BTG International Limited (Boston Scientific Corporation)
• Inventors: Chan, Kam Yuen, Bateman, Andrew
• Primary Examiner(s): Grimm, Siegfried H.
• Application Number:
  US08/976,950
• Time in Patent Office: 631 Days
• Field of Search: 331/2, 329/325, 329/326, 329/346, 329/360, 329/308, 330/10, 330/103, 332/127, 332/128, 332/144, 332/162, 332/103
• US Class Current: 332/103
• CPC Class Codes: H03C 1/06 Modifications of modulator to reduce distortion, e.g. by feedback, and clearly applicable to more than one type of modulator
• CPC Class Codes: H03F 1/0294 using vector summing of two or more constant amplitude phase-modulated signals

Abstract

An apparatus is disclosed for processing an input signal. The apparatus includes two feedback loops for generating output signal components from the input signal. Each loop contains an oscillator, which has a frequency or phase which is variable in response to a control signal, and a comparator for generating the control signal. The oscillator generates a loop output signal which forms one of the components of the output signal. The apparatus also includes a combiner for combining the loop output signals to produce the output signal. For each loop, the apparatus also produces a feedback loop operating signal, these signals being dependent on the output signal and in phase quadrature with one another. One input of the comparator in each loop receives the feedback loop operating signal, and the other input of the comparator receives a component of the input signal. The apparatus also continuously ensures that the output signal is stable whatever the phase of the output signal relative to that of the input signal.

Claims

1. Apparatus for processing an input signal to generate a combined signal, said apparatus comprising

first and second feedback loop units for generating, from said input signal, first and second loop output signals, respectively, and ensuring that the loop output signals have a phase relation corresponding to one among a set of predetermined phase relations,

said first feedback loop unit comprising a first voltage controlled oscillator, having one of a frequency and a phase which is variable in response to a signal v₁, for generating a first oscillator signal, said first loop output signal being based at least in part on the first oscillator signal, and a first comparator for generating a first control signal, the signal v₁ being based at least in part on the first control signal,

said second feedback loop unit comprising a second voltage controlled oscillator, having one of a frequency and a phase which is variable in response to a signal v₂, for generating a second oscillator signal, said second loop output signal being based at least in part on the second oscillator signal, and a second comparator for generating a second control signal, the signal v₂ being based at least in part on the second control signal, and

combining means for combining the loop output signals and outputting a combined signal, and

means for providing first and second feedback loop operating signals, based at least in part on the combined signal and in phase quadrature with one another, and for each loop, applying the feedback loop operating signal to one input of the comparator

another input of the comparator being coupled to receive a corresponding one of a first loop input signal and a second loop input signal, and

signal-stability means for continuously stabilizing the combined signal by ensuring that the combined signal is stable whatever the phase of the combined signal relative to the input signal, said signal-stability means receiving the input signal and outputting the first and second loop input signals.

2. Apparatus according to claim 1 wherein the means for providing the feedback loop operating signals includes

an oscillator having quadrature output signals, and

first and second mixers, one for each loop, for generating the first and second feedback loop operating signals, the mixers both being coupled to receive the combined signal as one input, and to receive respective quadrature output signals from the oscillator as another input.

3. Apparatus according to claim 1 including an amplifier for each loop connected between the voltage controlled oscillator and a respective input of the combining means.

4. Apparatus according to claim 2 wherein

the input signal has Cartesian component signals x and y, and

the signal-stability means comprises means for providing an additional signal for the combining means which has the effect of so biassing the input signal that when the envelope of the unbiassed signal passes through zero the envelope of the biassed signal, as represented by the loop input signals, does not, and

the signal-stability means includes a signal-stability loop comprising a signal-stability comparator, signal-stability means for generating a loop output signal having a frequency or phase which is variable in response to a control signal, a signal-stability amplifier connected at the output of the signal-stability means for generating a loop output signal and a signal-stability multiplier for demodulating the amplifier output signal using a signal in phase with one of the quadrature output signals to provide one input to the signal-stability comparator, the other input to the signal-stability comparator being one of the x and y signals.

5. Apparatus according to claim 4 including

means for adding a proportion of the output of one of the first and second comparators to the feedback signal applied to the other of the first and second comparators.

6. Apparatus according to claim 2 including an amplifier for each loop connected between the voltage controlled oscillator and a respective input of the combining means.

7. Apparatus according to claim 6 wherein the signal-stability means comprises means for providing an additional signal for the combining means which has the effect of so biassing the input signal that when the envelope of the unbiassed signal passes through zero the envelope of the biassed signal, as represented by the loop input signals, does not, and

the input signal has Cartesian component signals x and y, and

the signal-stability means includes a signal-stability loop comprising a signal-stability comparator, signal-stability means for generating a loop output signal having a frequency or phase which is variable in response to a control signal, a signal-stability amplifier connected at the output of the signal-stability means for generating a loop output signal and a signal-stability multiplier for demodulating the amplifier output signal using a signal in phase with one of the quadrature output signals to provide one input to the signal-stability comparator, the other input to the signal-stability comparator being one of the x and y signals.

8. An apparatus according to claim 7 including means for adding a proportion of the output of one of the first and second comparators to the feedback signal applied to the other of the first and second comparators.

9. Apparatus according to claim 1, claim 2, claim 3, or claim 6, wherein the input signal has Cartesian components x and y, and, in each loop the signal-stability means and the comparators derive control signals v₁ and v₂ for the respective VCOs:

##EQU17## where k=the loop gain of first and second feedback loops, each of said feedback loops including a respective one of the feedback loop units,

r=the amplitude of the input signal as represented by the components x and y,

R=the amplitude of the output of the VCOs,

Δ

x=the difference between the x component of the input signal and the corresponding Cartesian component of the combined signal, and

Δ

y=the difference between the y component of the input signal and the corresponding Cartesian component of the combined signal.

10. Apparatus according to claim 9 wherein

the comparators are connected to derive Δ

x and Δ

y, and

the signal-stability means comprises

a signal-processor means connected to receive the components of the input signal and to generate the following signals;

##EQU18## and, multiplier means connected to receive the signals α

1, α

2, α

3, α

4, Δ

x and Δ

y and to generate the control signals v₁ and v₂ therefrom.

11. An apparatus according to claim 10 including a respective integration and addition circuit for receiving as a loop signal a respective one among the signals v₁ and v₂ and adding the integral of the loop signal to the loop signal.

12. Apparatus according to claim 9 wherein

the input signal has Cartesian component signals x and y, and

the signal-stability means comprises

addition means for adding the x and y signals,

difference means for deriving the difference between the x and y signals, and

a signal processor means connected to receive the x and y components of the input signal and the output signals of the comparators, and to derive the signals v₁ and v₂, and

wherein the comparators are connected to receive the outputs of the addition means and the difference means as the loop input signals.

13. An apparatus according to claim 12 including a respective integration and addition circuit for receiving as a loop signal a respective one among the signals v₁ and v₂ and adding the integral of the loop signal to the loop signal.

14. An apparatus according to claim 9 including a respective integration and addition circuit for receiving as a loop signal a respective one among the signals v₁ and v₂ and adding the integral of the loop signal to the loop signal.

15. Apparatus according to claim 1, claim 2, claim 3, or claim 6, wherein the input signal has Cartesian component signals x and y, and the comparators are connected to derive Δ

x and Δ

y where

Δ

x=the difference between the x component of the input signal and the corresponding Cartesian component of the combined signal, and

Δ

y=the difference between the y component of the input signal and the corresponding Cartesian component of the combined signal, and

the signal-stability means comprises

addition means for adding the x and y signals,

difference means for deriving the difference between the x and y components of the input signal, and

signal processor means connected to receive the outputs of the comparators, the addition means and the difference means, and to derive the signals v₁ and v₂.

16. An apparatus according to claim 15 including a respective integration and addition circuit for receiving as a loop signal a respective one among the signals v₁ and v₂ and adding the integral of the loop signal to the loop signal.

17. Apparatus according to claim 1, claim 2, claim 3, or claim 6, wherein

the signal-stability means comprises means for providing an additional signal for the combining means which has the effect of so biassing the input signal that when the envelope of the unbiassed signal passes through zero the envelope of the biassed signal, as represented by the loop input signals, does not.

18. An apparatus according to claim 17 including a respective integration and addition circuit for receiving as a loop signal a respective one among the signals v₁ and v₂ and adding the integral of the loop signal to the loop signal.

19. Apparatus according to claim 1, claim 2, claim 3, claim 4, claim 5, claim 6, claim 7, or claim 8, including a respective integration and addition circuit for receiving as a loop signal a respective one among the signals v₁ and v₂ and adding the integral of the loop signal to the loop signal.

20. Apparatus for processing an input signal to provide a combined signal, said apparatus comprising

a phase detector and an amplitude detector connected to receive the input signal and a feedback signal as inputs,

first and second means for generating first and second component signals having frequencies or phases which are variable in response to signals v₁ and v₂,

means for combining the first and second component signals in deriving the combined signal,

means for deriving the feedback signal from the combined signal or components thereof,

difference means for deriving the difference between the output signal of the phase detector and a correction signal derived from the output signal of the amplitude detector to generate the signal v₁,

summing means for deriving the sum of the correction signal and the output signal of the phase detector to generate the signal v₂, and

correction means for deriving the correction signal from the input signal to reduce the dependence of the amplitude response of the apparatus on the amplitude of the input signal.

21. Apparatus according to claim 20 including

mixer means for frequency translating the combined signal or components thereof in providing the feedback signal by an amount equal to the difference in frequency between the outputs of the said first and second means, and the input signal.

22. Apparatus according to claim 20 or 21 wherein the first and second means are VCOs of sensitivity c and receive signals v₁ and v₂ according to the equations ##EQU19## where Δ

φ and

Δ

r are the phase and amplitude differences, respectively, between the input signal and the combined signal,

r is the amplitude of the input signal,

R is the amplitude of the respective VCO output signals, and

k is the gain of the feedback loop formed by feeding the combined signal back to the detectors.

23. An apparatus according to claim 22 including a respective integration and addition circuit for receiving as a loop signal a respective one among the signals v₁ and v₂ and adding the integral of the loop signal to the loop signal.

24. Apparatus according to claim 20 or 21 wherein the first and second means are VCOs of sensitivity c and receive signals v₁ and v₂ according to the equations ##EQU20## where Δ

φ and

Δ

r are the phase and amplitude differences, respectively, between the input signal and the combined signal,

r is the amplitude of the input signal,

R is the amplitude of the respective VCO output signals, and

k is the gain of the feedback loop formed by feeding the combined signal back to the detectors.

25. An apparatus according to claim 24 including a respective integration and addition circuit for receiving as a loop signal a respective one among the signals v₁ and v₂ and adding the integral of the loop signal to the loop signal.

26. A method of processing an input signal to generate a combined signal including the steps of

using first and second feedback loops to generate, from said input signal, first and second loop output signals, respectively, and ensuring that the loop output signals have a phase relation corresponding to one among a set of predetermined phase relations,

for each loop, generating from a voltage controlled oscillator, having one of a frequency and a phase which is variable in response to a control signal, a respective one among the loop output signals,

combining the loop output signals and the input signal to derive a combined signal,

generating feedback loop operating signals, in phase quadrature with one another, from the combined signal, one for each loop, and

for at least one loop, comparing the feedback loop operating signal with a component of the input signal to provide the respective control signal and continuously ensure that the combined signal is stable whatever the phase of the combined signal relative to the input signal.

27. A method of processing an input signal to provide a combined signal, comprising

generating first and second component signals each having one of a frequency and a phase which is variable in response to a respective one among first and second control signals,

combining the first and second component signals to derive the combined signal,

deriving a feedback signal from the combined signal or components thereof,

deriving the difference between the output signal of a phase detector and a correction signal derived from the output signal of a amplitude detector to generate the first control signal,

summing the correction signal and the output signal of the phase detector to generate the second control signal, and

deriving the correction signal from the input signal to reduce the dependence of the amplitude response of the apparatus on the amplitude of the input signal.

28. Apparatus for processing an input signal, said apparatus comprising:

(a) a first feedback loop unit for receiving a first loop input signal and generating a first loop output signal, said first feedback loop unit comprising

(a1) a first comparator for receiving a first loop feedback signal and the first loop input signal and generating a first control signal; and

(a2) a first oscillator for generating a first oscillator signal, said first oscillator having a frequency or phase which is variable in response to a signal v₁, the signal v₁ being based at least in part on the first control signal;

(b) a second feedback loop unit for receiving a second loop input signal and generating a second loop output signal, said second feedback loop unit comprising

(b1) a second comparator for receiving a second loop feedback signal and the second loop input signal and generating a second control signal; and

(b2) a second oscillator for generating a second oscillator signal, said second oscillator having a frequency or phase which is variable in response to a signal v₂, the signal v₂ being based at least in part on the second control signal;

(c) a signal combiner for receiving a first loop output signal and a second loop output signal, the first loop output signal being based at least in part on the first oscillator signal and the second loop output signal being based at least in part on the second oscillator signal, and outputting a combined signal;

(d) means for providing first and second loop operating signals, the first and second loop operating signals being in phase quadrature with one another and each being based at least in part on the combined signal; and

(e) signal-stability means for receiving the input signal and outputting the first and second loop input signals,

wherein the first loop feedback signal is based at least in part on the first loop operating signal, and the second loop feedback signal is based at least in part on the second loop operating signal, and

wherein said first and second loop output signals have a phase relation corresponding to one among a set of predetermined phase relations, and

wherein said signal-stability means maintains a continuous stability of the combined signal regardless of the relation between the phase of the combined signal and the phase of the input signal.

29. An apparatus for processing an input signal, said apparatus comprising:

a phase detector for receiving the input signal and a feedback signal and outputting a phase signal;

an amplitude detector for receiving the input signal and the feedback signal and outputting an amplitude signal;

a first signal generator for generating a first component signal having a frequency or phase which is variable in response to a signal v₁ ;

a second signal generator for generating a second component signal having a frequency or phase which is variable in response to a signal v₂ ;

a signal combiner for combining the first and second component signals and outputting a combined signal;

a feedback circuit for receiving at least a portion of the combined signal and outputting the feedback signal;

a subtractor for outputting a difference of the phase signal and a correction signal to generate the signal v₁ ;

an adder for outputting a sum of the phase signal and the correction signal to generate the signal v₂ ; and

a correction signal generator for receiving the amplitude signal and outputting the correction signal,

wherein the correction signal causes a dependence of the amplitude response of the apparatus on the amplitude of the input signal to be reduced.

30. A method of processing a input signal, including:

using first and second feedback loops to generate first and second loop output signals, respectively, from said input signal, said first and second output loop signals being substantially phase-matched with respect to each other,

for each loop, generating a corresponding one of the first and second loop output signals from a voltage controlled oscillator, said voltage controlled oscillator having a frequency or phase which is variable in response to a corresponding one among first and second control signals,

combining the loop output signals and the input signal to derive a combined signal,

for each loop, generating a feedback loop operating signal from a corresponding one of the loop operating signals, the feedback loop operating signals being in phase quadrature with one another, and

comparing one among the feedback loop operating signals with a component of the input signal to provide the first control signal,

wherein the continuous stability of the combined signal is maintained regardless of the relation of the phase of the output signal to the phase of the input signal.

31. A method of processing an input signal, said method comprising:

generating a first component signal having a frequency or phase which is variable in response to a first control signal,

generating a second component signal having a frequency or phase which is variable in response to a second control signal,

combining the first and second component signals to derive a combined signal,

deriving a feedback signal from a signal based at least in part on the combined signal,

deriving the difference of an output signal of a phase detector and a correction signal to generate the first control signal, said phase detector receiving the input signal and the feedback signal,

summing the correction signal and the output signal of the phase detector to generate the second control signal, and

deriving the correction signal from an amplitude detector, said amplitude detector receiving the input signal and the feedback signal, said correction signal causing a dependence of the amplitude response of the apparatus on the amplitude of the input signal to be reduced.