ADS1298: The performance difference between the internal reference and an external reference

Wang Zeyu

Part Number: ADS1298
Other Parts Discussed in Thread: OPA350, REF5025

Hi, Team, hope everything goes well with you all~

My question is about the performance differences between the internal reference and an external reference when deploying the ADS129x series-based system, ADS1298 for instance.

Currently, optimal system performance is crucial for our application scenarios. After checking the related description in the ADS1298 datasheet, we found there are not too many details about the reference voltage, such as noise level and stability, etc., and this datasheet just proposes an example based on REF5025 and OPA350 solution. My question is if an external reference will perform better than the internal reference in terms of the collected signal quality, such as ECG measurement? In addition, is there any guidance document when using an external reference?

Meanwhile, if a multi-channel system, which means more than one chip will be used, is designed and how to determine how many reference chips will be needed given the driven capability and noise issue?

Looking forward to your reply, and thanks ahead for the help from our community!

Zeyu

over 2 years ago

0 Nick Zahabizadeh over 2 years ago

TI__Expert 4134 points

Hello Zeyu,

I'll be copying the same response here since this is the same post as the other thread.

There's a couple pros and cons to each configuration. An external reference could be more accurate than than the internal, but it would also require extra design from your side to make sure the layout doesn't inadvertently add noise to your system. Using the internal reference is faster for design time and the noise performance is usually fine for most ECG applications of our customers. However, using the internal reference limits you to only two output voltages: 2.4 and 4V.

Like I mentioned, the performance using the internal reference is sufficient for most ECG applications, so most of our customers opt for that route.

In multi-AFE designs, one external reference should be able to deliver for all the AFEs cascaded together, just please note that this is assuming your design/layout for the external reference reduces any extra noise for the reference.

Kind regards,
Nick

0 Wang Zeyu over 2 years ago in reply to Nick Zahabizadeh

Prodigy 40 points

Hi, Nick, thanks for your reply, I really appreciate them. This is a copy from another thread~ you could respond to any one of them.

I still felt confused about those questions. My question is:

As you mentioned that an external reference with extra designs could be more accurate than an internal one, could you give me some suggestions or detailed guidelines for an external reference design, such as layout suggestions or filtering strategy? Although the performance is sufficient when an internal reference is used for ECG monitoring in most cases, we want to evaluate the optimal performance, i.e., when approximating the theoretical or optimal performance of the chip.

Zeyu

0 ChienChun Yang over 2 years ago in reply to Wang Zeyu

TI__Mastermind 19815 points

Hi,

Sorry for the late reply.

For internal reference voltage layout designs or suggestions, please refer to page 41 to 45 in https://www.ti.com/lit/ug/sbau171d/sbau171d.pdf

For external reference voltage, please refer to

page 54 https://www.ti.com/lit/ug/sbau171d/sbau171d.pdf

the external reference generators (U3 and U4) and driver buffer. NOTE: U3, U4, and driver buffer are not installed. The externally provided reference voltage can be set to either 4.096V or 2.5V, depending on the analog supply voltage. Measure TP3 to make sure the external reference is correct. The settings for the external reference is described in Table 10.

and

Figure 32 in https://www.ti.com/lit/ds/symlink/ads1298.pdf?ts=1649779822929&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FADS1298

suggests use REF5025.

Page 22 ~ 23 in

https://www.ti.com/lit/ds/symlink/ads1298.pdf?ts=1649779822929&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FADS1298

Table 1 to Table 4 show measurements taken with an internal reference. The data are also representative of the ADS129x noise performance when using a low-noise external reference such as the REF5025.

Hi Zeyu,

Do you have/use EVM for ADS1298?

Thanks

0 ChienChun Yang over 2 years ago in reply to ChienChun Yang

TI__Mastermind 19815 points

Hi Zeyu,

Do you have/use EVM for ADS1298?

Thanks

0 ChienChun Yang over 2 years ago in reply to ChienChun Yang

TI__Mastermind 19815 points

Hi,

This ticket/thread has been pending for more than 1 week.

I am closing this ticket/thread.

Please open another ticket/thread if there is question.

Thanks

Data converters

Data converters forum

ADS1298: The performance difference between the internal reference and an external reference