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Old 23rd October 2021, 06:55 AM   #1341
altor is offline altor  Israel
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This was my best result from 90389q2m with compensation.
At 7kHz THD is worse, but maybe due to ADC.
This ADC was a little bit noisy, I will try to re-test when Cosmos will come.
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File Type: png M1293_1khz_0db_44.png (108.8 KB, 123 views)
File Type: png M1293_7khz_0db_44.png (107.5 KB, 123 views)
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Last edited by altor; 23rd October 2021 at 06:57 AM.
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Old 23rd October 2021, 10:05 AM   #1342
JensH is offline JensH  Denmark
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ADCs and DACs for audio instrumentation applications
Quote:
Originally Posted by syn08 View Post
Jens, I was myself not able to bring a ES9038Q2M chip under -110dB THD+N at -1dB (with compensation), that was an heroic effort that included selecting the chip(s) (and destroying a couple of boards in the process). The -110dB i also the number that I see for the best commercial DAC implementations spec, although I don't think they are selecting the chips, so my boards (4 layers) could be 1-2dB less than optimal.

I believe -105dB @-1dB (without compensation) is a fair stating point to tweak the THD compensation, but you need to find out if it is the noise or the THD dominating the THD+N. I suspect it is the THD, so compensating may bring you to about the same numbers as above. I am using OPA1612 in the IV.
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Originally Posted by IVX View Post
Just take a look to the ESS 9038Q2M demoboard and make the same, with compensation you'll see THD+N a bit less than -120db(depends on the chip noise performance), without compensation probably -117db(depends on the chip distortions performance).
Thanks for your feedback.

syn08: I measured THD, not THD+N. Anyway, the noise is relatively low, so I am primarily concerned about the THD for now. The noise can probably be reduced slightly by using a lower noise power supply. I will probably use an op-amp based AVCC to get very low noise.
I have tried with different IV's. The first one with 2xLME49990. The present one with a socket, having tested OPA1612 and OP1656. The results are very similar. I don't have a balanced to single ended op-amp on the output, relying instead on the differential input of the analyzer (RTX6001).

IVX: I am certainly far away from the -117dB without compensation. And that is what's worrying me a bit. My unit is 12dB worse. Could that be due to the circuit/layout or due to variation between chips?

altor: Your results look quite good. Do you have a number for the THD without compensation?
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Old 23rd October 2021, 10:23 AM   #1343
IVX is offline IVX  Ukraine
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Quote:
I am certainly far away from the -117dB without compensation. And that is what's worrying me a bit. My unit is 12dB worse. Could that be due to the circuit/layout or due to variation between chips?
sure, I throw out about 4% of ES9038Q2M to get DR 123db(A) for 9038SG3(ES9038Q2M+AD8397 THD+N -117-115db).
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Old 23rd October 2021, 10:26 AM   #1344
IVX is offline IVX  Ukraine
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Quote:
Originally Posted by altor View Post
This was my best result from 90389q2m with compensation.
At 7kHz THD is worse, but maybe due to ADC.
This ADC was a little bit noisy, I will try to re-test when Cosmos will come.
do not trust Spectraplus for THD+N ar any noise-related calculations, it is wrong.
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Old 23rd October 2021, 11:31 AM   #1345
syn08 is offline syn08  Canada
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Quote:
Originally Posted by altor View Post
This was my best result from 90389q2m with compensation.
At 7kHz THD is worse, but maybe due to ADC.
This ADC was a little bit noisy, I will try to re-test when Cosmos will come.
Interesting, how much is 0dBFS at your DAC output? For me, 0dB is always about 4Veff. It would also be interesting to see your numbers at -0.5dB, -3dB is quite low.
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Old 23rd October 2021, 01:45 PM   #1346
altor is offline altor  Israel
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Quote:
Originally Posted by JensH View Post

altor: Your results look quite good. Do you have a number for the THD without compensation?
Cannot find a screen shoot. Will measure with Cosmos.


Quote:
Originally Posted by syn08 View Post
Interesting, how much is 0dBFS at your DAC output?
2.8Vrms.

Quote:
For me, 0dB is always about 4Veff. It would also be interesting to see your numbers at -0.5dB, -3dB is quite low.
Picture above was at -3dB.
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Old 23rd October 2021, 01:53 PM   #1347
altor is offline altor  Israel
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But I should mention, that I do not really believe in THD measurements less than 0.00008% with my AK5394 based ADC, because ESS compensation always compensate DAC+ADC harmonics.
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Old 23rd October 2021, 02:42 PM   #1348
JensH is offline JensH  Denmark
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ADCs and DACs for audio instrumentation applications
The AK5394A is a great ADC, but at these levels a notch filter should be used.
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Old 23rd October 2021, 02:51 PM   #1349
gentlevoice is offline gentlevoice  Denmark
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ADCs and DACs for audio instrumentation applications
@IVX: thanks for your clarification on my questions ;-)

Cheers,

Jesper
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