KD494
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If I'm reading correctly, if you have 2V full-scale signal, you've also got 100mV of noise (regardless of what the ADC adds). That's a signal-to-noise ratio of 26dB, not so good.
Have you considering averaging? If you can integrate over a number of samples, you can lower your noise floor.
Hi,
Your circuit looks good.
I recommend to run an FFT on the sampled data find out if there is one (or more) dominant noise frequency.
If yes, you could clean the source of this noise instead of manipulating your sensor signal.
Are you interested in signal frequencies down to DC or is there any limit.
To keep noise low..the first amplifier in chain should have the highest gain.
Is there a cable between sensor and ADC? (Or is the sensor mounted on the same PCB?)
Do you know the sensor's source impedance?
Klaus
For averaging, you first need to run your ADC at a higher sampling rate. For eg: if you double the sampling rate by 2x, on averaging you will get 3 dB advantage or 0.5 bit in ENOB.
As suggested in earlier posts, you can find out the dominant source of noise at the ADC input and clean that first.
Eddy current sensor:
They are low impedance, isolated and I assume you are not interested in DC signal.
Then you could try a signal transformer to "amplify" your signal voltage.
But I´d try this:
(I´d avoid the true instrumentation amplifier and use a high gain first Opamp stage to decrease noise.)
You have a 1.65V ...maybe you need to stabilize it with an Opamp and a filter.
Then connect one sensor input directely to his 1.65V
Then build a gain of -50 (up to gain -100) inverting stage with one LTC6253. (noniverting input to 1.65V, close to where the sensor is connected)
Maybe use 50Ohms and 2500 Ohms feedback.
You could also try LT6200-5 or LT6200-10. Less noise, high bandwidth.
If you increase ADC sampling rate, then .. with this method ... you just decrease ADC noise, but you can´t reduce signal noise.
But here definitely signal noise is the problem.
No, you don't need an Opamp, but I recommend to put at least 1 uF ceramics capacitor close to the sensor connection.maybe you need to stabilize it with an Opamp and a filter.
You say eddy current. Do you have the electrical source signal that cuses the eddy current? Or is it some mechanical source?
If you have the source, then you could correlate your signal to this source.
Just to be sure: you have a proper GND plane? Solid and clean..
In my eyes true noise is always not correlated to any signal. It is random in amplitude and random in frequency.I thought noise was either correlated or not and you have to deal with what you've got?
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