VCA821：I think there is something wrong in the picture of datasheet, Is there someone who have succeed simulating the circuit of this picture?

wen Zhang

Part Number: VCA821

Hello,

I think there is something wrong in the picture of datasheet, Is there someone who have succeed simulating the circuit of this picture? I simulated this circuit with Multisim，but can't achieve the function of AGC.

over 3 years ago

0 kai klaas69 over 3 years ago

Guru 140200 points

Hi Wen,

can you share your simulation file?

Kai

0 wen Zhang over 3 years ago in reply to kai klaas69

Prodigy 60 points

Hello Kai,

Thank you very much!

When I change the input of this circuit, the gain of the system has never changed. So I think maybe there is anything wrong.

Follow is my files, one is the simulation file of Multisim, the other is its picture.

Yours sincerely,

Wen

AGC_VCA821_10.2.5.zip

0 Hasan Babiker31 over 3 years ago in reply to wen Zhang

TI__Genius 15555 points

Hello Wen,

Would you be able to provide a screenshot of your transient simulation & labeling the issue? Can help you get this working on TINA or Pspice.

I've attached the circuit in TINA below:

AGC.TSC

Also you may want to take a look at this thread:

https://e2e.ti.com/support/amplifiers/f/14/t/152121?VCA820-Simulation-does-not-match-real-world-results

Best,

Hasan Babiker

0 Michael Steffes over 3 years ago in reply to Hasan Babiker31

Guru 47535 points

Your original sim Hasan using 1kHz was kind of in the bandwidth of the integrator, if you need to handle really slow signals, that integrator pole needs to be really low - here is your ckt with 1MHz input, The red curve is the control voltage, the green the output signal, Looks like it is working to me.

0 Hasan Babiker31 over 3 years ago in reply to Michael Steffes

TI__Genius 15555 points

Thanks Michael, it seems I wasn't allowing enough time in the transient sims to see this correction properly.

Best,

Hasan Babiker

0 Michael Steffes over 3 years ago in reply to Hasan Babiker31

Guru 47535 points

Or, you should have let R8 be 100k and extend the run time to capture to a final Vg value. The Vg was moving with the 1kHz signal which is why the waveform looked so bad.

0 wen Zhang over 3 years ago in reply to Hasan Babiker31

Prodigy 60 points

Thanks Hasan! It's very helpful to me.

Yours sincerely,

Wen

0 wen Zhang over 3 years ago in reply to Michael Steffes

Prodigy 60 points

Thanks Michael.

Yours sincerely,

Wen

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VCA821：I think there is something wrong in the picture of datasheet, Is there someone who have succeed simulating the circuit of this picture?