ADS1293 - remove RLD

Bill Tyler

Intellectual 290 points

Other Parts Discussed in Thread: ADS1293EVM, ADS1293

I am trying to create a design with just the RA + LA input.

Based on this thread https://e2e.ti.com/support/data_converters/precision_data_converters/f/73/t/407970

In the other pic I have shorted in4 to in1 RA. I have also tried changing SELRLD to go to in1 with the same results.

Am I missing something? Should something be hooked up to the RLDIN or RLDREF?

this is the baseline

over 10 years ago

0 Bill Tyler over 10 years ago

Intellectual 290 points

Some how some text was removed. I tried to say the configuration is an ads1293evm connected to the pc over usb.
Then a simulator connected to the evm to LA and RA.
In the baseline pic, RL is connected to RL on the evm.
In the second pic, I have shorted the RL to RA.

0 Bahram Mirshab over 10 years ago in reply to Bill Tyler

TI__Expert 3350 points

Here are the options when using two leads only.

ADS1293 system architecture is optimized for ECG systems with low-impedance connection of the patient to a right-leg-drive. When used in a 2-lead ECG system without the presence of the 3th lead, either of the following solutions could be taken to consideration in order to have functional lead-off-detection:

If you intend to use external input protection resistors on your product, then use an external MUX to bypass the input protection resistors and connect RLD to one of the leads (protection resistors still possible in the RLD path). You can use analog AC lead-off detection.

If you intend to have external input protection resistors, use the internal MUX to connect RLD to one of the leads. Analog AC LOD will be functional.

If you intend to use large leakage resistors to bias the patient’s common mode, the DC and analog AC lead-off-detection of ADS1293 will NOT work, in this case only the digital AC lead-off detection can be used in combination with the AFE.

0 Bill Tyler over 10 years ago in reply to Bahram Mirshab

Intellectual 290 points

So the issue seems to just be that lod was enabled, disabling lod results in a much better signal.

0 Bahram Mirshab over 10 years ago in reply to Bill Tyler

TI__Expert 3350 points

Then you need to use the AC lead off detection.

0 Bill Tyler over 10 years ago in reply to Bahram Mirshab

Intellectual 290 points

can you suggest the registers to update? i changed a few with no luck

0 Bahram Mirshab over 10 years ago in reply to Bill Tyler

TI__Expert 3350 points

I will ask the software engineer to provide you the optimal settings

0 Vishy Viswanathan over 10 years ago in reply to Bahram Mirshab

TI__Mastermind 21685 points

Please refer section 8.6.3, page 45.
Register LOD_CN: 0x14 // ACAD_LOD = 1, SHDN_LOD = 0, SELAC_LOD = 1, ACLVL_LOD = 00
Register LOD_EN:0x3F // enable IN1 to IN6 (modify this depending on how many inputs you have)
Register LOD_CURRENT:0x00
Register LOD_AC_CN:0x00 // excitation freq of 12.5kHz (see section 8.3.17)

0 Bill Tyler over 10 years ago in reply to Vishy Viswanathan

Intellectual 290 points

Thanks. I will check this out.
I also have an issue when trying to use my fingertips for the ecg signal. When I touch the simulator to the silver/silver chloride electrodes connected to in1 and in2 I get a good signal. However when I touch my fingers there is hardly any signal, just noise.

Any suggestions on resolving this?

0 Bahram Mirshab over 10 years ago in reply to Bill Tyler

TI__Expert 3350 points

I assume you are using one finger from your left hand and one from your right hand to connect to the inputs of the ADS1293. Is the silver/silver chloride electrode adhesive enough? If the electrodes are not pressed tight against the skin they would act like dry electrodes resulting in large impedance between your finger and the electrode. Try to lower the impedance by applying some water or some silver/silver chloride gel at the contacts between your finger and the electors to lower the impedance.

0 Bill Tyler over 10 years ago in reply to Bahram Mirshab

Intellectual 290 points

Yes, one finger from each hand. A dry electrode is what I am going for, any suggestions on handling the impedance?

0 Bahram Mirshab over 10 years ago in reply to Bill Tyler

TI__Expert 3350 points

You may want to try an active dry electrode, please see the attached article.rbme10.pdf

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ADS1293 - remove RLD