ADS1299

Hi,

The AC CMRR is tested with shorted input, and a 50/60Hz sine wave FS+/-0.3V signal is applied. Please refer to the datasheet note (2) for the test condition. The AC CMRR has a minimal value in the datasheet, so it is fully tested in the final production ATE test.

That is the info TI is allowed to shared/disclosed.

Thanks

Hi,

You're talking about note2 at the bottom of page 9 of the datesheet?

For example, now the power supply on the development board is +-2.5V, then the external signal source needs to use +-2.2V sine wave to provide signal input to ADS1299, PGA=1, then Vout= waveform peak-peak value in scope, CMRR=20lg(4.4V/Vout)?

Is that how CMRR is calculated?

thanks

Hi,

External signal source input signal Vpp=4.4V/50Hz signal, channel 2 of the development board P and N short, channel 2 output waveform peak-to-peak value 80uVpp

FFT

FFT Analysis

Calculation result: CMRR=20lg (4.4V/80uV) =94.8dB, but the upper computer interface display is 151dB, may I ask where the problem occurred?

thanks

That is how CMRR is "Measured"

Thanks

Hi,

The AC CMRR is tested with shorted input, and a 50/60Hz sine wave FS+/-0.3V signal is applied. Please refer to the datasheet note (2) for the test condition. The AC CMRR has a minimal value in the datasheet, so it is fully tested in the final production ATE test.

That is the info TI is allowed to shared/disclosed.

1. Add common-mode voltage according to note2 on page 9 of datasheet: -2.2V-+2.2V. There is a big difference between the result of CMRR and the result calculated by the software itself. For example, how much common-mode voltage to give, what special configuration of registers, etc.;

2. input noise is set as "input short" when we test, and the peak value of channel signal output is 6-8uVpp, which is quite different from that in the data manual. Could you please tell us how to measure it in detail?

3. How to measure the input impedance? Could you tell me in detail how to measure it?

Hi,

According to the CMRR calculation results of previous posts, as shown in the figure below:

I have some questions to ask:

1, TI software CMRR how to calculate, is it according to the calculation formula in the post, but FFT transformation after the output result of the unit is dB, and the input voltage unit is V, the two how to convert or refer to which benchmark to get dB

Hi,

The AC CMRR is tested with shorted input, and a 50/60Hz sine wave FS+/-0.3V signal is applied. Please refer to the datasheet note (2) for the test condition. The AC CMRR has a minimal value in the datasheet, so it is fully tested in the final production ATE test.

That is the info TI is allowed to shared/disclosed.

Could you tell me the specific calculation formula of CMRR？

Sorry, TI doesn't disclose that info.

Thanks

Hi,

Can you tell me how to test the input impedance of the development board?

Thanks

Hi,

I esclated&brought your questions to internal discussion.

I will need to discuss internally with other engineers to see what we can disclose and support.

Thanks for your patience, and apology for the delay.

Hi,

Looking forward to your reply

Thanks

Hi,

1. CMRR test: According to IEC 60601-2-26-2012 test standard, the signal from the signal source to the development board is 2.828Vpp/50Hz, P and N electrodes of channel 4 are short circuit, and the output signal of the test channel is as follows:

However, the actual test effect of the development board is shown as the figure below: the CMRR actually calculated by us is 79dB, while the upper computer software of TI is 162.32dB. May I ask whether the TI demo board will conduct post-processing on the output signal? So, how do we use the development board to test, how to operate to achieve the results of the development board?

2. Input impedance test: According to GB9706.227-2021 standard, the signal from the signal source to the development board is 0.67Hz/3.998V, and the signal is attenuated 1000 times by the attenuator, as shown in the following figure:

No series resistance enters the channel, and channel 4 outputs signal about 4mVpp, as shown in the figure below:

The 620K resistance in series enters the channel, and the output signal of channel 4 is shown in the figure below:

How should we measure the channel input impedance on the TI development board?

Thanks

Hi,

Thanks for the info.

I will need to discuss internally with other engineers to see what we can disclose and support.

Thanks for your patience, and apology for the delay.

Hi,

Looking forward to your reply.

Thanks

Hi,

We need more time for internal discussion.

Thanks for your patience.

Hi,

Here are some comments:

Regarding to input impedance, one could use 3458A Agilent Multimeter and Use 500mV to supply to the input of the current meter and connect the output of current meter to (+) channel input of the ADS, and observe the current reading to be around 200pA to know input impedance is > 1Gohm.

We are still waiting for other engineers to see whether he can comments on how CMRR is calculated&implemented in the GUI.

Thanks

Hi,

Regarding to CMRR -

Could you try to do

1. internal short test on the same channel and see whether the reported CMRR reported make sense.

2. Do CMRR test in other channel and see whether the reported CMRR is closer to your calculation.

Thanks

Hi,

Because we do not have 3458A Antitron multimeter, the DC input impedance cannot be tested for the time being. How to measure the AC input impedance of the development board?

Thanks

Hi,

I will need to have more internal discussion to see what we can disclose.

Thanks

Hi,

Looking forward to your reply

Thanks

Need more time for internal discussion.

Hi,

Could you tell me how the discussion on the CMRR and AC input impedance parameter test method of the development board is going?

Thanks

Hi,

We still need more time for internal discussion.

Thanks

Hi,

After searched the datasheet and discussed with internal engineers. There is no AC input impedance parameter and test.

Thanks

Hi,

We have known the AC input impedance parameters and the test, so what kind of test method should we use for CMRR to meet the standard of GB9706?

Thanks

Hi,

What might be the GB9760?
We don't support to meet the standards, regulations and/or certifications otherwise than what are mentioned in the datasheet.
Customers will need to decide and determine the peripheral parts and design with the regulatory, QA, QC teams to meet any standards or regulation requirements.
Thanks