elskardio

PCM1808 ADC frequency response not flat
« on: March 17, 2021, 08:50:40 AM »
Hi Guys,

I'm presently experimenting with the PCM1808 ADC. The schematic is identical to the Datasheet.

The frequency response is far from flat in the top end. (please see the attached image, captured at 48KHz)

Looking at the curve, it's almost like there's a LPF with a -3dB point at 44Khz.

Should i be able to get a flat response from this ADC or it has limitations?

Thanks for your input



elskardio

Re: PCM1808 ADC frequency response not flat
« Reply #1 on: March 17, 2021, 02:19:16 PM »
Ok
Turns out the input needed to be properly buffered  ::)
Here's the frequency response at 48KHz.

Re: PCM1808 ADC frequency response not flat
« Reply #2 on: March 18, 2021, 09:19:09 AM »
Id been meaning to buy in a couple of those boards for testing myself . Theres also a PCM1802 board for a few euros on ebay which I think has slightly better noise/thd specs than the 1808.
So thats interesting you have level frequency response to around 22khz @48khz FS.
Could you repeat your tests at 96khz ?
PCM1802 quotes SNR as 105db , parraleling the inputs might get you 3db better and perhaps a balanced input using both channels push/pull might improve performance by another small but usefull margin.
Keep up the good work . 
 



mhelin

Re: PCM1808 ADC frequency response not flat
« Reply #3 on: March 29, 2021, 05:49:41 AM »
Here's the frequency response at 48KHz.
How about the SNR (with inputs grounded, or with signal at various levels)?


 

Related Topics

  Subject / Started by Replies Last post
16 Replies
6761 Views
Last post January 16, 2007, 10:17:30 AM
by gar381
26 Replies
12035 Views
Last post July 05, 2012, 04:28:11 PM
by Rossi
1 Replies
1785 Views
Last post May 15, 2012, 03:19:48 PM
by Andy Peters
9 Replies
2431 Views
Last post February 26, 2019, 12:01:57 PM
by craigmorris74