ADS8864 analog inputs.

martin b

Other Parts Discussed in Thread: ADS8864

I’m reading the data sheet for the ADS8864 and I’m a bit confused as to some of the terminology. On the front page it states.

“The ADS8864 is a 16-bit, 400-kSPS, single-ended input, analog-to-digital converter (ADC)… The device supports unipolar single-ended analog inputs in the range of –0.1 V to VREF + 0.1 V”

Found on page 34 is

“Figure 69. Differential Input DAQ Circuit for Lowest Distortion and Noise at 400 kSPS”,

with a diagram showing some sort of differential input configuration.

This has me a bit confused as to how ADC differential inputs work as this device is claimed to be single ended, is there any way of clearing this up for me?

Than

m.b

over 9 years ago

0 Harsha Munikoti over 9 years ago

TI__Expert 5705 points

Hi Martin,

Before answering your question, I would recommend that you change the "Account" and "Company" information on your profile as soon as possible. We do not entertain profanity on our forums. Thank you.

Now onto your question... In devices with single-ended inputs, the analog input is measured with respect to power supply GND. The ADS8864 measures its input with respect to AINM which is allowed to be upto +/-100mV relative to the ADC's power supply GND. In other words, the effective input that will be converted is (AINP-AINM) and in this sense, the ADS8864 has a differential input structure, or more precisely a pseudo-differential input structure, rather than single-ended (of course AINM can be connected to GND for a single-ended configuration).

Please refer to the following blog post for more details on SAR ADC input types:

http://e2e.ti.com/blogs_/b/precisionhub/archive/2014/06/20/input-considerations-for-sar-adcs

Best Regards,
Harsha

0 martin b over 9 years ago in reply to Harsha Munikoti

Intellectual 560 points

Harsha I've made some changes,.....?...did you change my settings?

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ADS8864 analog inputs.