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Zhoating -

Make sure you have the path C: \work\LabView Files\LV86\libmmb0\saved created on your hard drive.  The program should create the text file if it doesn't exist.

Hi Greg,

Thanks for your reply and I appreciate it.

Now I am able to run the vi but I still can not make communication with the board using the vi I run. When I run it and connect the board to my PC at the same time, the statement at the top right corner of the UI which is green (shown as follow) says:

'Locating binary file'
then 'Reading binary file'
then 'USB connection established'
then 'No firmware found...downloading'
then 'Download failed...reset the hardware'

Then I got this:

'The firmware load has failed due to time out condition. Please reset the hardware to continue loading the firmware'

'Connection and FW load failed
Please check your connections/configuration and try again'

I also check the thread and I found this:  http://e2e.ti.com/support/data_converters/precision_data_converters/f/73/t/164743.aspx

My situation is similar but a little bit different from that guy because I try to use and run the vi in LabView environment. Is that possible? Does this have something to do with the incompatibility  of Windows 7? I thought it might be OK because it is run in the LabView environment. Am I wrong about this?

Thanks a lot for your patience.

Regards,

Zhaoting Du

Zhaoting -

The compatibility with WIN7 is a driver issue, not necessarily a LabVIEW problem.  I would expect to see behavior similar to what you describe when you are trying to use this on Win7.  We are currently upgrading the software to a new version of LabVIEW to go along with the driver upgrade.

Hi Greg,

Here is one question I want to ask about those PGAs. From the user's guide and data sheet, I know I could set the gain of those PGAs to 1, 2, 3, 4, 6, 8 or 12 by setting the 4th bit to 6th bit of the CHnSET registers. My question is that will that be possible if I want to tune the PGAs' gain other than those 7 values? How does this gain programming mechanism work? Are there any details about this?

Wish your reply and thanks for any help and advice.

Regards,

Zhaoting Du

Zhaoting -

The gain settings of the PGA are fixed gain settings that are design into the silicon, so I am unsure of what you would propose to modify.  You could potentially add gain/attenuation in an external circuit that you would control (external op-amp/PGA), if you wanted more control.  So you would pre-condition the signal before the ADS1298, but this circuit could potentially influence noise or signal integrity. 

Hi Greg,

Thanks for your reply.

I just want to know how the gain of those PGAs are programmed. On data sheet page 25, I notice that the gain is controlled by the tunable resistor R1, which is 20 kohms for gain = 6. And I also know that the gain is controlled by the CHnSET registers (4th bit to 6th bit). So the question is how the registers' values affect those tunable resistors and hence change the gain of PGAs. Could you please tell me the simple mechanism of it? Any detail schematics?

Regards,

Zhaoting Du

Zhaoting -

So from your question previously, you are want to change the gain of the PGA, correct?  The circuit that you noted on Figure 28 is how the internal settings of the CHnSET registers (as you noted) afftect the PGA.  As the register values change, so does the value of R1 (as you noted).  The resistor scales accordingly to set the gain of the PGA, so the value of R1 can be calculated out to the required value.

So if you are trying to "tweak" the gain, you need to be putting a attenation/gain stage in front of the mux to accomplish this since you cannot change any of the resistor values used to set the gain.  If this is not your objective, please clarify what you are trying to achieve so that we can better answer your question.

Hi Greg,

I am happy to try the new software.

My email is: xxxxx@gmail.com

Hi Greg,

Thanks for your reply.

Yes, we are trying to control the PGAs' gain.

From what you said, my understanding is the gain of PGAs themselves can not be changed to other values except those 7 (1, 2, 3, 4, 6, 8, 12), or, the gain values of PGAs could not be tuned continuously. We have to add external circuits to make the gain of the whole path constant. Is that correct?

I also asked about the gain control mechanism of those PGAs. How does the change of registers lead to the value's change of R1?

By the way, does TI have PGAs which could be programmed like this way and used together with the ADS1298?

Regards,

Zhaoting Du

Yes...you are correct in that there is no method to change the gain settings of the chip.  The gain adjustments that you are talking about will need to be done externally with an op-amp/resistor divider circuit.

The PGA is controlled via register bits that switch in/out different resistor values to set the gain.  This is strictly controlled internally on the device, so the operation cannot be changed or modified.

We do have some PGAs and op-amps that are available.  The trick is that for ECG performance you need extremely low noise values, which is challenging to achieve with external signal conditioning circuitry.  PGAs in gerenal aren't going to be real good for low noise applications.  INA333 and OPA209/211 might be a good place to start for low noise gain/attenuation.  You might check out the article in the following post on the Linear Apps Forum regarding noise source for INA type devices and other amplifier information.

http://e2e.ti.com/support/amplifiers/precision_amplifiers/f/14/p/202887/720670.aspx#720670

Hello Greg,

I am working with Zhaoting together. Is there any method of controlling these swithes by program? Such as in labview or add another DSP stage?

Thanks a lot!

JINGYI

The switches are controlled by the per channel gain settings. You may not access them directly. Review the device datasheet and EVM user's guide.

Jingyi -

I understand that you want to control the PGA settings.  However, per the previous discussions, these are controlled internally on the silicon and are fixed to the values that are available shown in the datasheet.  They are not available for programming.

External gain/attenuation (see previous post) circuitry will need to be implemented to achieve the constant gain that you desire for your circuit

Hi Greg,

Could you please send me the LabView Source code of the Windows7 ADS1298 software?

Regards,

Zhaoting Du