Method and apparatus for amplifying, modulating and demodulating

• US 5,719,527 A
• Filed: 11/22/1994
• Issued: 02/17/1998
• Est. Priority Date: 05/08/1992
• Status: Expired due to Fees

• Current Assignee: British Technology Group Ltd.
• Original Assignee: British Technology Group Ltd.
• Inventors: Bateman, Andrew, Chan, Kam Yuen
• Primary Examiner(s): Grimm, Siegfried H.
• Application Number:
  US08/335,841
• Time in Patent Office: 1,183 Days
• Field of Search: 331/2, 331/23, 332/127, 332/128, 332/144, 332/162, 329/325, 329/326, 329/346, 329/360, 330/10, 330/103
• US Class Current: 330/10
• 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

A highly efficient linear amplifier and/or modulator and demodulator comprising first and second feedback loops is provided. Each loop processes a component of the input signal and the component signals are recombined at, for example, a summing junction 18. The feedback signals for each loop are dependent upon the output signal and are in phase quadrature. The input signal is separated into I and Q signals, which are also in phase quadrature, by a component separator 10.

Claims

1. Apparatus for processing a first signal to generate a second signal, the processing arrangement comprising:

input means for receiving said first signal and generating first and second process reference signals of said first signal;

first and second feedback loops, each loop comprising a voltage controlled oscillator responsive to a control signal for generating a loop output signal and a comparator for generating the control signal;

combining means for combining the loop output signals from each loop for deriving the second signal;

means for providing first and second feedback loop operating signals, dependent on the combined loop output signals from the combining means and in phase quadrature with one another;

the feedback loop operating signals being applied to corresponding inputs of the comparators of the first and second loops, respectively, and

another input of each comparator being coupled to receive a respective one of said first and second process reference signals.

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

a quadrature oscillator having quadrature output signals;

and

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

3. Apparatus according to claim 2, wherein the first signal is an input signal for amplification or modulation and the second signal is an output signal.

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

5. Apparatus according to claim 3, arranged as a modulator including first and second input terminals for the application of first and second Cartesian components of said first signal connected as the process reference signals for the comparators of the first and second loops, respectively;

and

an output terminal of the combining means;

whereby a modulated signal appears at said output terminal which is the input signal frequency translated by the frequency of the quadrature oscillator.

6. Apparatus according to claim 5, including a component separator for receiving a modulating input signal and deriving Cartesian components thereof for application to the said first and second input terminals.

7. Apparatus according to claim 1, arranged with amplification of the second signal wherein the means for providing the feedback loop operating signals comprises means for deriving quadrature-phase signals from the second signal as the first and second feedback loop operating signals.

8. Apparatus according to claim 1, including control means for controlling respective connections within or between components for the two feedback loops both in respect of determining the said connections and also whether the said connections include signal inversion, the control means operating in accordance with signal characteristics to ensure that stable operation occurs.

9. Apparatus according to claim 8, wherein the signal characteristics are the signs of one input signal for each comparator, and the respective connections are connections between the comparators and the voltage controlled oscillators.

10. Apparatus according to claim 1, wherein the process reference signals are Cartesian components of the first signal, including phase control means for controlling the phases of the process reference signals to ensure stable operation of the apparatus.

11. Apparatus according to claim 10, wherein the phase control means comprises a first phase shifter for subtracting the phase of the feedback loop out signals from that of both the process reference signals before application to the comparators, and

a second phase shifter for subtracting the phase of the first signal from that of both the first and second feedback loop operating signals before application to the comparators.

12. Apparatus according to claim 11 including rectifying means for taking the modulus for each output of the first phase shifter before application to the comparators.

13. Apparatus according to claim 10, wherein the phase control means comprises

means for providing a signal representative of the amplitude of the first signal as one process reference signal and means for providing a constant signal as the other process reference signal;

a phase shifter controlled by first and second phase control signals for shifting the phases of the first and second feedback loop operating signals before application to the comparators; and

means for providing signals representative of the phases of the Cartesian components as the first and second phase control signals.

15. Apparatus according to claim 1, including

detection means for detecting zero crossings in an envelope of the first signal;

and

noise reduction switching means for changing over the voltage controlled oscillator between loops when a zero crossing is detected by the detection means.

16. Apparatus according to claim 1, wherein the process reference signals are Cartesian components of the first signal wherein each voltage controlled oscillator generates Cartesian components of the loop output signal, and the apparatus includes:

first and second means for combining corresponding Cartesian loop output signals to provide the first and second feedback loop operating signals, and third combining means for combining the output of the first and second combining means to provide the second signal.

17. Apparatus according to claim 16, including first and second amplifiers connected between the first combining means and the third combining means, and the second combining means and the third combining means, respectively.

14. Apparatus for processing a first signal to generate a second signal, the processing arrangement comprising:

input means for receiving said first signal and generating first and second process reference signals of said first signal;

first and second feedback loops, each loop comprising a voltage controlled oscillator responsive to a control signal for generating a loop output signal and a comparator for generating the control signal;

combining means for combining the loop output signals from each loop for deriving the second signal;

means for providing first and second feedback loop operating signals, dependent on the combined loop output signals from the combining means and in phase quadrature with one another;

the feedback loop operating signals being applied to corresponding inputs of the comparators of the first and second loops, respectively, and

another input of each comparator being coupled to receive a respective one of said first and second process reference signals;

detection means for detecting zero crossings in one of the first signal or the envelope thereof; and

noise-reduction switching means for changing over the voltage controlled oscillator between loops when a zero crossing is detected by the detection means.

18. A method of processing a first signal to generate from said first signal a second signal comprising the steps of:

providing said first signal and generating first and second process reference signals of said first signal;

using first and second feedback loops, to generate a loop output signal for each loop having a frequency which is variable in response to a control signal;

combining the loop output signals from each loop for deriving the second signal;

generating feedback loop operating signals, in phase quadrature with one another, from the, combined loop output signals; and

comparing each feedback loop operating signal with a respective one of said first and second process reference signals to provide the respective control signals.

19. A method according to claim 18 comprising the steps of:

generating respective quadrature signals, and

generating the feedback loop operating signals includes mixing the second signal with the respective quadrature signal to provide the feedback loop operating signal.

20. A method according to claim 18, wherein the first signal is an input signal for modulation or amplification and the second signal is an output signal.

21. A method according to claim 20 including amplifying the loop output signals before combining them.

22. A method of modulation according to claim 20, wherein Cartesian components of the input signal are used as the respective process reference signals, and the second signal forms the output signal.

23. An amplifying method according to claim 18, wherein quadrature phase versions of said second signal form the feedback loop operating signals.

24. A method according to claim 18, including controlling connections between the two feedback loops, determining whether said connections include signal inversions, and altering the said connections to ensure stable operation occurs.

25. A method according to claim 18 including

providing Cartesian components of the first signal as the respective process reference signals, and

controlling the phases of the respective process reference signals to ensure stable operation.

26. A method according to claim 18 including

detecting zero crossings of the first signal or envelope thereof, and

changing connections between the two feedback loops when said zero crossings occur.

27. Apparatus for demodulating an input signal having an associated carrier frequency, comprising:

a summing circuit for combining the input signal to be demodulated with first and second feedback signals to output an error signal;

first and second feedback loops each receiving the error signal from the summing circuit and providing to the summing circuit said first and second feedback signals replicating Cartesian components of the input signal;

an oscillator for providing to said first and second feedback loops corresponding first and second operating signals at the carrier frequency but in phase quadrature with one another; and

each loop comprising;

a comparator for generating a control signal derived at least in part from the error signal, and

a voltage controlled oscillator having at least one of a frequency or phase characteristic which varies in response to the control signal, the oscillator generating in response to the control signal one of the first and second feedback signals; and

first and second out-of-loop mixers, one associated with each of said first and second feedback loops, for receiving corresponding ones of the first and second operating signals and first and second feedback signals for outputting therefrom respective output signals.

28. An apparatus according to claim 27, wherein each loop further comprises:

an amplifier connected between the voltage controlled oscillator for that loop and the summing circuit to receive and amplify the corresponding first and second feedback signals.

29. An apparatus according to claim 28 wherein:

the summing circuit comprises;

first, second and third input terminals, and an output terminal,

the first input terminal receiving the first feedback signal,

the second input terminal receiving the second feedback signal,

the third input terminal receiving the input signal, and

the error signal appearing at the output terminal, the error signal representing deviations in phase or frequency between the first and second feedback signals and the input signal;

each loop further comprising;

an in-loop mixer to receive the error signal from the summing circuit and a corresponding one of the first and second operating signals from the oscillator and to combine them into a in-loop mixer output provided to the comparator, and

wherein the comparator for each loop generates the control signal by comparing the in-loop mixer output for that loop with a zero magnitude signal.

30. An apparatus according to claim 29, further including means for combining the respective output signals from the first and second out-of-loop mixers to derive a signal representative of modulation carried by the input signal.

31. A method of demodulating an input signal having an associated carrier frequency, comprising the steps of:

combining the input signal to be demodulated at a summing circuit with first and second feedback signals for producing an error signal therefrom;

receiving the error signal from the summing circuit at first and second feedback loops and providing to the summing circuit from the loops said first and second feedback signals replicating Cartesian components of the input signal;

providing to said first and second feedback loops corresponding first and second operating signals at the carrier frequency but in phase quadrature with one another; and

within each loop;

mixing, within the loop, a corresponding first and second operating signal with the error signal to output an in-loop mixed signal,

comparing the in-loop mixed signal to a reference signal to generate a control signal, and

generating a voltage controlled oscillation signal having at least one of a frequency or phase characteristic which varies in response to the control signal to thereby generate in response to the control signal one of the first and second feedback signals;

receiving, at mixers outside of the loops, corresponding ones of the first and second operating signals and corresponding ones of the first and second feedback signals to provide respective output signals associated with each of said loops.

32. A method according to claim 31, further comprising:

combining in the summing circuit the first and second feedback signals and the input signal in such a way that the error signal deprived therefrom represents deviations in phase or frequency between the first and second feedback signals and the input signal; and

in each loop, comparing the in-loop mixed signal to a zero magnitude reference signal.