Info about "Digital Decimation Filtering" block in PDM->PCM converters

Hello mk102,

The 64x/32x/16x is simply the order of the filter so the steepness of the cutoff frequency, the out of band lobing and the flatness in band will all be the tradeoffs. We did publish these filter responses in the datasheet. I really cannot go into more detail on a public forum. This is entering into proprietary techniques. 

So this would have to be discussed under NDA. What are your concerns and what are you seeing in the datasheet specifications that are either concerning or missing?

Dave T

Hello mk102,

Can you share some of the performance details you are seeing? There are a lot of variables for sure. Clock jitter on the BCLK and of course on the sampling clock for the PCM is also a factor. There is no PLL inside so any jitter present on the BCLK input is divided down and goes out on the PDM clock. It is divided which helps a little. 

This part does have really good performance. How are you feeding the analog into the mic or other PDM source? The issue could be there if there is a lot of out-of-band energy and we are just taking the PDM signal that some other part produced so it is subject to the sigma-delta modulator that is creating the PDM signal. 

If you need to talk to me you should have my contact info. 

Dave T