ads 1298 conversion time

Dear sir/madam,

We are in the design process of 12 channel ECG machine for the same i want to use ADC ADS 1298 delta sigma ADC, now i need to know the conversion time for ads 1298 when using 8-channels @500samples for second each channel, we tried for getting the conversion time in the data sheet we didn't understood that parameter so please help me on this regard.

Awaiting for your quick responce

Please mail me the reply to my mail: anjaneyulu.d'at'skanray.com

Hi anjaneyulu,

The conversion time of the ADS1298 is essentially the inverse of the sample rate, so 500sps is 2milli-seconds.  The ADS1298 has eight independent ADC that run simultaneously, so to maintain the data rate and retrieve all conversion results, you need to run the serial interface fast enough to get the status byte and eight channels of data out of the part every 2ms.  For twelve channels, you have 2 parts and therefore two status bytes (each at 24-bits) plus 12 channels of data (also 24-bits each), so you're looking at 336 SCLKS every 2ms.

Thank you  Mr. Tom, For your quick response,

I am looking for ADC conversion time in number of clock cycles, i have calculated with respect 2msec sec 500 sps, i.e 4000 cycles. I have a doubt in conversion of adc 4000 cycles are required ? If it is so can you please explain me the way it is converting.

Please reply me : anjaneyulu.d'at'skanray.com

Thank you

Hi again anjaneyulu,

The ADS1298 is a delta-sigma converter.  The delta-sigma is different from devices like a successive approximation register (SAR) converter in that the output data is given in terms of data rate.  The input is oversampled (and converted) at the CLK speed, the conversions are accumulated and decimated and the results are then sent to the output at a lower data rate, 500SPS in your case.  I know we've got some presentation materials that might help you out here - I'll track them down and send you links.

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Dear Tom,

Thanks for your response, please share the links regarding presentation material.

Regards

Anjaneyulu

Sorry for the delay here...

This link takes you to some basic information regarding the way Delta-Sigma converters 'do what they do':

Nuts and Bolts of Delta-Sigma Converters