Noise compensated synchronous detector system

• US 4,675,613 A
• Filed: 07/11/1986
• Issued: 06/23/1987
• Est. Priority Date: 08/11/1983
• Status: Expired due to Term

• Current Assignee: Agilent Technologies, Inc.
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Naegeli, Andrew H., Carp, Stuart L.
• Primary Examiner(s): Miller, Stanley D.
• Assistant Examiner(s): Roseen, Richard
• Application Number:
  US06/883,464
• Time in Patent Office: 347 Days
• Field of Search: 328/14, 328/15, 328/133, 328/150, 328/165, 328/166, 328/167, 328/138, 307/527, 307/529, 307/556, 307/543, 331/1 R, 455/296, 455/312, 455/309, 329/50, 329/130, 330/302, 330/303, 330/306
• US Class Current: 327/5
• CPC Class Codes: H03D 1/2245 using two quadrature channels H03D1/2209 takes precedence

Abstract

A circuit in a synchronous detector system is provided to minimize and compensate for the errors induced by phase modulation and additive noise in the system. In one embodiment a first-order correction of such errors is achieved by equipping the synchronous detector system with a constant loop filter noise bandwidth and an RMS detector. A resolution filter passing the detected system signal to the RMS detector for correction is made to have a noise bandwidth identical to the loop filter noise bandwidth.

Claims

1. A noise-compensated synchronous detector system comprising:

a synchronous detector having a first signal and a second signal synchronized to said first signal as input signals;

synchronizer means for providing said second signal to said synchronous detector, wherein said synchronizer means has a fixed noise bandwidth B;

a resolution filter having said fixed noise bandwidth B coupled to an output of said synchronous detector; and

an RMS detector having an input coupled to an output of said resolution filter for compensating noise induced errors in said output of said synchronous detector, said RMS detector having a detector system output;

whereby noise and perturbation effects are reduced at said detector system output because said synchronizer means and said resolution filter have the same noise bandwidth B.

2. The synchronous detector system as in claim 1 wherein said synchronizer means further comprises:

a loop filter having variable gain for establishing a fixed loop noise bandwidth B;

a variable oscillator coupled to an output of said loop filter and responsive thereto to provide a loop signal;

phase shift means coupled to an output of said variable oscillator, said phase shift means being responsive to said loop signal and operative to phase shift said loop signal by 90 degrees to develop said second signal at an output thereof; and

a phase detector having said first signal and said loop signal as input signals, said phase detector having an output which develops an output signal responsive to said input signals, said output of said phase detector being coupled to an input of said loop filter as an input signal.

3. A noise-compensated synchronous tracking detector system comprising:

an input port for receiving a first input signal;

a first frequency converter having as input signals said first input signal and a loop signal to provide a first frequency converter output signal at an output thereof;

a loop filter having said first frequency converter output signal connected thereto as an input signal, said loop filter having a variable gain to maintain a constant noise bandwidth B;

a variable oscillator coupled to an output of said loop filter and responsive thereto to provide said loop signal to said first frequency converter;

a second frequency converter having as input signals said first input signal and said loop signal shifted by 90 degrees in phase to provide a second frequency converter output signal;

a resolution filter having a bandwidth equal to said constant noise bandwidth B coupled to an output port of said second frequency converter for receiving said second frequency converter ouput signal; and

an RMS detector connected to an output port of said resolutin filter to provide a detected signal which is noise-compensated due to the fact that said loop filter and said resolution filter have the same constant noise bandwidth B.

4. A noise-compensated nonsynchronous tracking detector system comprising:

an input port for receiving a first input signal;

a frequency converter having as input signals said first input signal and a second input signal;

a phase detector coupled to an output of said frequency converter;

a loop filter coupled to an output of said phase detector;

a variable oscillator coupled to an output of said loop filter, said vairable oscillator being operative to provide said second input signal, where said frequency converter, phase detector, loop filter, and variable oscillator form a closed loop having a predetermined noise bandwidth B;

a resolution filter having a predetermined noise bandwidth 2B coupled to said output of said frequency converter; and

an average detector coupled to an output of said resolution filter for developing a detector system output;

wherein noise and perturbations in said detector system output are reduced as a result of said resolution filter having a predetermined noise bandwidth 2B which is twice the noise bandwidth B of said closed loop.

5. A noise-compensated synchronous detector system comprising:

a synchronous detector having a first signal and a second signal synchronized to said first signal as input signals;

synchronizer means for providing said second signal to said synchronous detector, said synchronizer means having a fixed noise bandwidth B and including;

a loop filter having variable gain for establishing said fixed loop noise bandwidth B, said loop filter having;

integrator means having an input and an output, where said input of said integrator means is coupled to said output of said phase detector;

variable gain amplifier means having an input and an output, where said input of said variable gain amplifier means is coupled to said output of said phase detector; and

summation means having inputs coupled to said outputs of said integrator means and said variable amplifier means, said summation means having an output comprising said output of said loop filter;

a variable oscillator coupled to an output of said loop filter and responsive thereto to provide a loop signal;

phase shift means coupled to an output of said variable oscillator, said phase shift means being responsive to said loop signal and operative to phase shift said loop signal by 90 degrees to develop said second signal at an output thereof; and

a phase detector having said first signal and said loop signal as input signals, said phase detector having an output which develops an output signal responsive to said inputs signals, said output of said phase detector being coupled to an input of said loop filter as an input signal;

a resolution filter having said fixed noise bandwidth B coupled to an output of said synchronous detector; and

an RMS detector having an input coupled to an output of said resolution filter to compensate for noise induced errors in said output of said synchronous detector, said RMS detector having a detector system output;

whereby noise and perturbation effects are reduced at said detector system output because said synchronizer means and said resolution filter have the same noise bandwidth B.

6. The synchronous detector system as in claim 5 wherein said variable amplifier means includes:

amplifier means having an input and an output;

variable feedback means coupling said input and said output of said amplifier means; and

control means for controlling said variable feedback means.

7. The synchronous detector system as in claim 6 wherein said variable feedback means includes a variable resistance, and wherein said control means includes digital processing means and digital-to-analog means responsive to said digital processing means and operative to control said variable resistance.

8. A noise-compensated synchronous tracking detector system comprising:

an input port for receiving a first input signal;

a first frequency converter having as input signals said first input signal and a loop signal to provide a first frequency converter output signal at an output thereof;

a loop filter having said first frequency converter output signal connected thereto as an input signal, said loop filter having a variable gain to maintain a constant noise bandwidth B, said loop filter including;

integrator means having an input and an output, where said input of said integrator means is coupled to said output of said first frequency converter;

variable gain amplifier means having an input and an output, where said input of said variable gain amplifier means is coupled to said output of said first frequency converter; and

summation means having inputs coupled to said outputs of said integrator means and said variable amplifier means, said summation means having an output comprising said output of said loop filter;

a variable oscillator coupled to an output of said loop filter and responsive thereto to provide said loop signal to said first frequency converter;

a second frequency converter having as input signals said first input signal and said loop signal shifted by 90 degrees in phase to provide a second frequency converter output signal;

a resolution filter having a bandwidth equal to said constant noise bandwidth B coupled to an output port of said second frequency converter for receiving said second frequency converter output signal; and

an RMS detector connected to an output port of said resolution filter to provide a detected signal which is noise compensated because said loop filter and said resolution filter have the same constant noise bandwidth B.

9. The synchronous detector system as in claim 8 wherein said variable amplifier means includes:

amplifier means having an input and an output;

variable feedback means coupling said input and said output of said amplifier means; and

control means for controlling said variable feedback means.

10. The synchronous detector system as in claim 9 wherein said variable feedback means includes a variable resistance, and wherein said control means includes digital processing means and digital-to-analog means responsive to said digital processing means and operative to control said variable resistance.

11. In a synchronous detector system including a phase lock loop, an improved phase lock loop filter comprising:

loop input means;

integrator means having an input and an output, where said input of said integrator means is coupled to said loop input means;

variable amplifier means having an input and an output, where said input of said variable amplifier means is coupled to said loop input means;

summation means having a plurality of inputs and an output, where said output of said integrator means is coupled to one of said inputs of said summation means and said output of said variable amplifier means is coupled to another one of said inputs of said summation means; and

loop output means coupled to said output of said summation means.

12. The phase lock loop filter as in claim 11 wherein said variable amplifier means includes:

amplifier means having an input and an output;

variable feedback means coupling said input and said output of said amplifier means; and

control means for controlling said variable feedback means.

13. The phase lock loop filter as in claim 12 wherein said variable feedback means includes digital processing means and digital-to-analog means responsive to said digital processing means and operative to control said variable resistance.