ADS1298ECGFE-PDK: Verwendung des Demonstrations Kit als EMG System

Hi,

RA, RL, LA and LL are common notations and knowledge for ECG applications for Right Arm, Right Leg, Left Arm and Left Leg.

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We are not EMG electrodes and placement topology experts, and there could be many different varieties of EMG electrodes placement topology depending on customers researches/applications/products, so our support might be limited.

But we can give some high level general guidelines - e.g.

Does customer measure EMG in differential method like ECG?

i.e. for example Is the signal of interest to be measured by "the difference between 2 nodes(electrodes)" e.g. signal from Node A minus(-) signal from Node B? 

If yes, then they could connect the EMG's differential signals e.g. Node A to ADS's + input and Node B to ADS's - input.

It's customers decision to decide where the Node A and Node B come from Subject(or Unit) Under Measurement i.e. Animal or an EMG simulator(suggested when using with EVM).

Thanks

Hi Chien,

Please see customer feedback below:
"I want to implement the electrodes in differential mode, therefore I need a Reference for the negative input of the channels (you refered to as ADS's - input). The reference currently is, as I uderstand the avarage given by the wilson central terminal (WCT). This is connected via JP16 and internally routed form three of the channels 1-4.
Currently I am using a secondary electrode array as my Reference. Basically I am comparing each positive input potential to this baseline.
The WCT seems to have potential to reduce the area required by the elekctrodes by a significant margin (approx. 1/3). Unfortunately the current combination of the software regestry entries and physical configuration is giving me trouble right now. The Reference value is heavily influenced by the ECG_RL.
Is there a way to reconfigure the WCT, or would it be easiest just to feed in a other input signal via JP16?"

Thank you and best regards,
Gerald

Hi,

I will get back to you around 6/22.

Thanks

Hi Chien,

I would like to gently follow up on the status of our customer concern. We hope to hear again from you. Thank you

Hi,

WCT is used for ECG acquisition, and to create/generate the WCT, the WCT requires multiple signals inputs, so that the ADS's internal OpAmp does the analog calculation to generate/create the WCT output.

Customer may take a look of the ADS1298 datasheet section 9.3.1.7.3 Wilson Central Terminal (WCT) and Chest Leads and do some study of WCT online to see whether this is what they want for their EMG application. Again, WCT is calculated&created by algebra from other inputs signals.

So, to create WCT in ECG application, "WCT voltage is defined as the average of right arm (RA), left arm (LA), and left leg (LL) electrodes", i.e. 3 input signals.

Does customer want to provide 3 input signals? 

Also, page 37 -

"Only use the WCT node to drive very high input impedances (typically greater than 500 MΩ). A typical application connects this WCT signal to the negative inputs of a ADS129x for use as a reference signal"

Also, note that - 

"The inputs of the amplifiers are chopped, and the chop frequency varies with the data rates of the ADS129x.

The chop frequency for the three highest data rates scale 1:1.

For example,

at a 32-kSPS data rate, the chop frequency is 32 kHz in HR mode with WCT_CHOP = 0.

The chop frequency of the four lower data rates is fixed at 4 kHz.

When WCT_CHOP = 1, the chop frequency is fixed to highest data rate frequency (that is, fMOD / 16).

The chop frequency appears at the output of the WCT amplifiers as a small square wave riding on dc. y

The amplitude of the square wave is the offset of the amplifier and is typically 5 mVPP.

"

Chop frequency depends on fMOD and fCLK and the selection of data rate.

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Not sure what does customer mean by  " secondary electrode array as my Reference."?

How many WCT amplifiers do they plan to use? And, do they power up the desired WCT amplifier AND power down the unused WCT amplifier?

What do they mean by "The Reference value is heavily influenced by the ECG_RL."?  Could they try compare with and without the ECG_RL?

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Installing JP16 is just to allow the WCT output to be able to be used. Whether customer really wants to use/route the WCT output to any inverting/negative(-) input pins, they can decide whether to install any of jumpers from JP26 to JP30's  1-2 positions.

Thanks