OPA347: DC Output Smoothing decay rate too long

Dave

Part Number: OPA347
Other Parts Discussed in Thread: TINA-TI, INA827, , TS5A9411

I have a design which will smooth a differential input signal from an In Amp, provide some gain with a potentiometer and output the signal. This is all fine but when the signal is removed, the output takes too long to settle due to the integrator capacitor. The decay rate is far too long. Is there a better way of doing this?

I have tried a precision peak detector but this adds time for the signal to ramp up.

This is a single supply design. The input frequency is from 10Hz to 1KHz.

I want an output signal like the one below but when I remove the input signal, I want the output to be 0V within 200ms.

I could do with simulating the sinewave for a small finite amount of time and then seeing the decay rate when the signal disappears, is there a way to do this in Tina-TI?

The design is attached, I hope someone can help.DC Smoothing circuit.TSC

over 2 years ago

0 kai klaas69 over 2 years ago

Guru 140200 points

Hi Dave,

I would do it with a switch:

dave_opa347.TSC

Kai

0 Caro Walter over 2 years ago in reply to kai klaas69

TI__Genius 17497 points

Hey Dave,

Is there a reason you chose to use AD8226? We have a TI equivalent in INA827.

Additionally I would add an Riso for U5 like you have in U12, before driving the 22nF.

All the best,
Carolina

0 Dave over 2 years ago in reply to kai klaas69

Prodigy 90 points

I have managed to get rid of the decay by draining the capacitor using a comparator and transistor. When the input voltage at VF1 drops below 0.1V, I turn on

a FET to drain the Integrator Capacitor C11 but it does drain it too well. I could do with something to smooth out some more.

0 Dave over 2 years ago in reply to Caro Walter

Prodigy 90 points

I will check out the INA827 In Amp, I used this as I have used this In Amp before.

Can you elaborate more about the changes to U5 please.

0 kai klaas69 over 2 years ago in reply to Dave

Guru 140200 points

Hi Dave,

unfortunately, you short circuit the output of OPA347 by this, which might not be a good idea when doing this repeatedly and frequently under normal operation. You could discharge the integrating capacitor by the help of DG419, as shown in this link:

https://www.physics.utoronto.ca/~astummer/Archives/2004%20nS%20Pulse%20Integrator/nS%20Pulse%20Integrator.html

Kai

0 Dave over 2 years ago in reply to kai klaas69

Prodigy 90 points

I am trying to look for an Analogue Switch to use in my simulation but cannot find one, can you point me in the right direction?

0 Jerry Madalvanos over 2 years ago in reply to Dave

TI__Mastermind 22361 points

Hey Dave,

https://www.ti.com/cross-reference-search/singlepart?searchTerm=DG419

Here is a list of TI equivalent parts for the DG419.

Best,
Jerry

0 Caro Walter over 2 years ago in reply to Jerry Madalvanos

TI__Genius 17497 points

Hey Dave,

You may add a SPST switch in TINA-TI, is this what you mean by analog switch?

I have moved the thread to precision amplifiers to help with the comparison between AD8226 and INA827.

All the best,
Carolina

0 Dave over 2 years ago in reply to Caro Walter

Prodigy 90 points

No, lol. I have added the TS5A9411 to my simulation and it appears ok.

I will add a few more parts and a bit more testing but it looks ok.

Thanks

0 kai klaas69 over 2 years ago in reply to Dave

Guru 140200 points

Hi Dave,

Caro isn't so wrong. I usually take the TINA-TI's "voltage controlled switch" and add the parasitic capacitances and series resistance manually. Sometimes I choose a discrete FET, when I'm interested in charge injection issues, as discussed here:

https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/940064/how-to-improve-the-accuracy-of-peak-detector-as-high-as-posssible/3473673?tisearch=e2e-sitesearch&keymatch=yatao%20AND%20kai#3473673

Kai

0 Raymond Zhang1 over 2 years ago in reply to Dave

TI__Mastermind 47796 points

Hi Dave,

Here may be another way to do it under Controlled Source Editor.

You may configure two input voltage/current sources and compare the input and derive a desired output ( as an example).

if V(N1) > V(N2), then

Vout will retain V(N1) signal

Else

Vout = 0

endif

Controlled Switched Controller 03082022.TSC

I am not proficient in this feature. I did try the functionality a while ago and it works good. The Controlled Source can be also used to generate PWM or other digital signals as well).

If you have additional questions, please let me know.

Best,

Raymond

0 Dave over 2 years ago in reply to Raymond Zhang1

Prodigy 90 points

Hi Raymond,

Thank you for this, it has come in very handy.

Always learning something new.

Dave

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OPA347: DC Output Smoothing decay rate too long