Interfacing the TLV2544 A/D to C5509 DSP

Mehdi,

On Oct 10, 2009, at 10:08, s...@gmail.com wrote:
> > Note: One thing I forgot to point out earlier is that a microphone-
> > based system probably will not be susceptible to sample phase
> issues,
> > because the time delays due to the distance between the mic and the
> > sound source will vary and will far outweigh the sample latency. In
> > other words, this is most likely a non-issue. In fact, that may
> > explain why the data sheets do not even mention the timing of the
> > sample process.
> >
> > Brian Willoughby
>
> You are right, but the sample phase issues is so important for me
> because I want to obtain time delay of arrival (TDOA) between 2
> microphones.
In your case, I suggest that you research available ADC chips until
you find one which is capable of sampling 2 channels in sync with
each other. I'm sure there will be a way to interface such a chip to
the C5509, but you must first find the right chip.

I believe that you originally mentioned a 3-channel setup, so if your
3rd channel does not need to be perfectly aligned, you can
potentially use a separate chip. If you need all 3 channels to be
sampled in sync, then you're going to have a hard time finding a chip
already designed for that, and in that case you'll have to design a
more complex analog circuit for sample-and-hold.

> >These are good points. Unless the chip data sheet specifically
> talks about
> >simultaneous sampling performed by multiple devices then sampling
> phase >alignment is likely to be an issue.
> >And if the data sheet doesn't talk about attaching multiple
> devices to >the same serial port bus or "TDM bus", then it's not
> going to work >anyway. The device must specifically support a
> "multichannel" or "chain" >mode of some type.
>
> >-Jeff
>
> Thanks Jeff, but I don't understand your good points! You mean that
> attaching multiple devices to the same serial port we can get
> simultaneous samples? If so, How?
>

No, there's probably no way to communicate to two devices
simultaneously on the same serial port, at least not without severe
hacking.

You could potentially tie the DX pin (e.g. DX0) to the serial input
on two ADC chips which align their sample time to the incoming serial
commands. However, you'd need two separate DR pins (e.g. DR0 and
DR1) in order to obtain the separate sample values from the two chips.

I think that what Jeff is alluding to is that there are several
different ways of addressing an SPI chip. Some chips have a Chip
Select pin which must be active the entire length of a command and
data transfer. Other chips require the Chip Select pin to only be
active for each individual word of the transfer, and thus there would
be multiple select transitions during a multiple word command and
data transfer. Still other chips have an address coded into the
serial command and do not use a Chip Select pin at all - these chips
often have some way to wire each chip differently so that you can
assign a different address to each chip.

The bottom line is that you need to study the data sheet for the
individual serial ADC chip and make sure that you understand how the
chip is selected or addressed. If you don't, and you attach multiple
chips to the same port, then they'll trip over each other and the
data will be corrupted.

My point was that most serial ADC chips use the serial command to
align the sample time. You cannot communicate to multiple devices
simultaneously on a serial port - they must be accessed serially,
thus the name. Therefore you cannot sample simultaneously unless you
use multiple serial ports in parallel. You still have to make sure
that the technique you select is compatible with the addressing and
sample timing scheme for which your chosen ADC chip is designed.

Brian Willoughby

Sound Consulting Start a New Thread

Mehdi Hosseini-

>> Note: One thing I forgot to point out earlier is that a microphone-
>> based system probably will not be susceptible to sample phase issues,
>> because the time delays due to the distance between the mic and the
>> sound source will vary and will far outweigh the sample latency. In
>> other words, this is most likely a non-issue. In fact, that may
>> explain why the data sheets do not even mention the timing of the
>> sample process.
>>
>> Brian Willoughby
>
> You are right, but the sample phase issues is so important for me because I want to obtain time delay of arrival
> (TDOA) between 2 microphones.
>
>>These are good points. Unless the chip data sheet specifically talks about
>>simultaneous sampling performed by multiple devices then sampling phase >alignment is likely to be an issue.
>>And if the data sheet doesn't talk about attaching multiple devices to >the same serial port bus or "TDM bus", then
>> it's not going to work >anyway. The device must specifically support a "multichannel" or "chain" >mode of some type.
>
>>-Jeff
>
> Thanks Jeff, but I don't understand your good points! You mean
> that attaching multiple devices to the same serial port
> we can get simultaneous samples? If so, How?

You have to find a device that supports multichannel and/or multi-chip operation, and clearly says so in its data
sheet. Suggest to search Cirrus Logic and Analog Devices for "multichannel" and "daisy chain".

-Jeff Start a New Thread

>You have to find a device that supports multichannel and/or multi-chip
>operation, and clearly says so in its data
>sheet. Suggest to search Cirrus Logic and Analog Devices for
>"multichannel" and "daisy chain".

Thanks for your good points, Brian and Jeff
I think I have to read dustsheets more and more until find a perfect ADC for my work :)

--
Seyed Mehdi Hosseini Start a New Thread