Electronics > Beginners
Op amp not working out as planned
(1/11) > >>
netdudeuk:
Hi

I've got a AD9833 DDS Signal Generator Module sending out a 1KHz sine wave.  I'm supposed to be amplifying it with a NJM5532 op amp (https://www.njr.com/semicon/PDF/NJM5532_E.pdf) running from the same 5v rail.  However, the output looks poor, being clipped and with ringing.

Here's how I have the op amp configured.

Any idea why the output signal looks so bad and why the gain isn't -10 ?

Thanks

Andy Watson:

--- Quote from: netdudeuk on March 04, 2018, 06:31:04 pm --- running from the same 5v rail. 

--- End quote ---
Just the one supply ?
You will need both positive and negative power supplies to use any op-amp in that configuration. Also, the NE5532/34 requires a lot of headroom - If you have +5 and -5V supplies, the chip will only work properly with a signal within the range +3 to -3 (I think - look at the "common mode" range on the datasheet).

netdudeuk:
Hi

Thanks for the prompt reply.

Yes, I'm using a single 5v supply.

I was taking the design from here but without wanting to add the offset voltage -

https://youtu.be/ts-JqEVzvDo?t=6m35s

He looks to be using a single supply rail here -

https://youtu.be/ts-JqEVzvDo?t=7m44s

He also uses a capacitor in the feedback loop which I don't have.

Mechatrommer:

--- Quote from: netdudeuk on March 04, 2018, 07:00:30 pm ---I was taking the design from here but without wanting to add the offset voltage -
https://youtu.be/ts-JqEVzvDo?t=6m35s

--- End quote ---
that is used for audio amplification from microphone which usually in 100mV range. multiply by 10 in your application is 1Vpp well within the supply range. your application is 600mV input that is 6Vpp output well outside your supply range, hence the clipping. to avoid clipping you should either reduce your input Vpp or increase the voltage supply range or reduce the opamp gain.
Andy Watson:

--- Quote from: netdudeuk on March 04, 2018, 07:00:30 pm ---I was taking the design from here but without wanting to add the offset voltage -

--- End quote ---
With a single supply it is not optional - you need to bias the op-amp to around 2.5V - as is shown at approximately 6:45. You will also require the decoupling caps - depending on what you are using as your signal source.
Navigation
Message Index
Next page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod