Phase detector for PLL with low SNR

In summary: A PLL circuit is used to automatically adjust frequency to a resonance f. Because frequency is at resonance the phase is very unstable. By saying low signal I mean the amplitude is small and it kinda dissapears in the noise which makes it hard to detect. Any particular questions?Interesting! In summary, a PLL circuit is used to automatically adjust frequency to a resonance. The signal is analog and measured with a voltmeter. The system's purpose is to measure a surface potencial with vibrating zond of a material. Because frequency is at resonance the phase is very unstable. By saying low signal I mean the amplitude is small and it kinda dissapears in the noise which makes it hard to detect. Any scheme idea
  • #1
C12H17
4
0
I'm making a system with PLL. Here's more or less a principal scheme. What happens here is that the signal in this compensating system becomes really low and phase detector might not work properly. What I want to ask, what type or how to make a phase detector which can detect phase correctly from a very low signal. Any scheme idea?
 

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  • #2
Interesting!

Can you supply some more detail? Are the signals digital or analog? When you say "low signal" do you mean you wish to detect very small phase error, or that the amplitude of the signal is small.
 
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  • #3
The system's purpose is to measure a surface potencial with vibrating zond of a material. The signal is analog and measured with voltmeter. PLL circuit is used to automatically adjust frequency to a resonance f. Because frequency is at resonance the phase is very unstable. By saying low signal I mean the amplitude is small and it kinda dissapears in the noise which makes it hard to detect. Any particular questions?
 
  • #4
Why don't you use the output of your generator to drive two synchronous detectors but maintain a phase difference between the generator inputs to the two synchronous detectors of 90 deg? This is typically referred to as I & Q demodulation.

You would take the analog outputs of both synchronous detectors, square the values and add them together. The sum represents the amplitude of your signal. Note that this method works even if neither phase from the generator is in phase with your signal. The effect of noise can be minimized by the use of a low pass filter on the output.

To accomplish the squaring function you can either use A/D converters to convert to digital values which you square and then either convert back to analog or use the digital values. Or you can use an analog multiplier such as the AD633ANZ to square the analog values directly.

If you look around you may be able to find ICs that do the I & Q demodulation for you.
 
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  • #5
C12H17 said:
The system's purpose is to measure a surface potencial with vibrating zond of a material. The signal is analog and measured with voltmeter. PLL circuit is used to automatically adjust frequency to a resonance f. Because frequency is at resonance the phase is very unstable. By saying low signal I mean the amplitude is small and it kinda dissapears in the noise which makes it hard to detect. Any particular questions?
This doesn't make sense to me. Since the slope dphi/df is maximal on resonance, doesn't your feedback loop have maximal gain there? I'd expect best stability on resonance.
 
  • #6
I have to say I'm a little confused as well. The phase should be fairly stable at resonance if the Q is decent. At the very least, it sounds like you're going to need an amplifier with a bandpass filter to get enough signal to drive your phase detector.
 
  • #7
any small frequency deviation from the resonance makes a phase to change from +90 to -90. So I need f to be stable at resonance and phase to be stable. My lecturer said that the gain will be minimal.
Honestly, I have no idea what I'm doing here.
 
  • #8
C12H17 said:
any small frequency deviation from the resonance makes a phase to change from +90 to -90.
Phase with respect to what - your generator?

So I need f to be stable at resonance and phase to be stable. My lecturer said that the gain will be minimal.
How is f created? If you have a pickup, what kind of pick up is it? Are you able to amplify and filter f before you try to phase lock to it?

Can you clarify why your instructor instructor said gain will be minimal? Can you give us a better description of your setup?
 
  • #9
C12H17 said:
any small frequency deviation from the resonance makes a phase to change from +90 to -90. So I need f to be stable at resonance and phase to be stable. My lecturer said that the gain will be minimal.
Honestly, I have no idea what I'm doing here.


That sort of phase shift around resonance is typical. The swing thru zero is what marks the resonant frequency.
 
  • #10
I have to ask, why are you using a PLL for this? If all you want is to provide stimulation to a resonant device, all you need is a simple signal generator tuned to the resonant frequency.
 

1. What is a phase detector for PLL with low SNR?

A phase detector is a device used in a phase-locked loop (PLL) to compare the phase of two signals and generate an error signal that is used to adjust the frequency of the output signal. In the context of a PLL with low signal-to-noise ratio (SNR), the phase detector is designed to operate effectively even when the input signals are weak and noisy.

2. How does a phase detector for PLL with low SNR work?

A phase detector for PLL with low SNR typically uses a combination of analog and digital processing techniques to accurately compare the phase of the input signals. It may also incorporate signal filtering and amplification to improve the signal-to-noise ratio before the phase comparison process.

3. What are the advantages of using a phase detector for PLL with low SNR?

One of the main advantages of using a phase detector designed for low SNR is its ability to operate effectively in environments with weak and noisy signals. This makes it a valuable tool for applications such as telecommunications, where signals may be subject to interference and distortion.

4. Are there any limitations to using a phase detector for PLL with low SNR?

While a phase detector for low SNR can improve the performance of a PLL in noisy environments, it may also introduce some additional complexity and cost to the system. Additionally, the effectiveness of the phase detector may be limited by the overall quality of the input signals.

5. How can a phase detector for PLL with low SNR be optimized for a specific application?

The design and optimization of a phase detector for low SNR will depend on the specific requirements and characteristics of the application. This may include factors such as the desired frequency range, input signal strength, and noise profile. Working with a skilled engineer or using computer simulation tools can help to ensure that the phase detector is well-suited for the intended application.

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