TPA3244EVM: Understanding the Gain of the Amplifier

Hello Paul,

The buffers are preset for a gain of 1.  I will need a little more information on your system set up.  Are you using single-ended or differential input?  Also are you sending a sine wave input signal?

Thanks,

Robert

Hi Robert,

Using a single ended input, I see the following:

C2 is my SE Input signal. C3 is the A/C output of the TPA3244EVM and C4 is the B/D output, both referenced to GND.  The math waveform is the difference between C3 and C4.  The scope is measuring a 100mVrms input and 1.57 Vrms output, approximately 15.7V/V gain.

For differential inputs, I see that the can seems to be about 8V/V:

This time, C1 is INB, C2 is INA, C3 is A/C, and C4 is B/D. 

Below is the AP configuration for the differential configuration.

Please let me know if there is more information you need.  

Thanks!

Paul

Hi Paul,

First great screenshots!
On the analog generator I noticed you have it set to 8ohms instead of 4ohms. I'm not sure that would be the cause of your problem but it is worth checking.

I changed it to 4Ω, no change. I think that field is for when you use Watts or dBm for input amplitude, but I'm not super familiar with the AP2722 yet.

Ok, I understand why SE input has 2x the gain of the differential input.  

Looking at the schematic, we can see that the RCA input A is buffered and inverted for INA, Then if J4 is set to SE, the same signal is buffered and inverted again for INB.  So this means that the actual differential inputs of the TPA3244 is seeing 2x the input amplitude of the original signal from the AP.  When if differential mode this circuit does not change the magnitude of the input.

But this still leaves me wondering why the TPA3244 circuit has a gain of approx 8X rather than 10X, is there some kind of attenuation with the output filter/LC?

Thanks!

Hi Paul,

I have to apologize.  I misunderstood your initial question regarding the op amps.  Yes you are correct, though the op amps are set to unity gain, if the signal is single-ended then the signal does get X2 to create a differential signal. 

I have also run the test using the information you provided and was able to recreate your results.  There does appear to be a gain closer to 8X.  Your assessment on it being the LC filter is the most likely cause of a majority of the loss seen.

Regards,

Robert

Thanks for the update!