I am doing my EEG project with ADS1298. As the datasheet said, the RLDREF is setted to (AVDD+AVSS)/2 in default. How can I define my own RLDREF value? The new RLDREF can be injected through any input of the channels? Or is there any jumper is designed for external RLDREF? This problem is not explained clearly in the datasheet, user guide.
Thanks a lot!
Welcome to our forum! If you take a look at the ADS1298 data sheet (page 67, figure 62) you will see that RLD_REF is able to be configured as an input pin. You can connect this internally to Vdd/2 or the WCT node, or you could use your own external source to drive the pin. The inverting terminal of the RLD amp can be connected to any input channel through the internal MUX (see page 21). On the ADS1298ECFE-PDK hardware, we did not provide a test point or jumper (sorry about that) to connect an external RLD_REF input, but there is R1/R2/R5 combination available on the EVM. You could input your own source directly to R5 (ADS1298 side) or install resistors in these locations (including a 4mm trim pot at R2) to get a variable input source for RLD_REF.
Thank you for your reply. I want to use the external RLD_REF, since there is no jumper for injection point, I want to route the RLD_REF to the WCT AMP. I need to set the Register4 (DRL_TO_WCT bit), but there is no setting column in the sofeware. How can I set the bit here? Can I write the mapping directly?
Look forward to you reply.
The RLD_REF bit is accessible in the CONFIG3 register found in the ADS1298ECG-FE GUI in the global channel registers section. On the ADS1298ECG-FE board, we did not include a jumper to give you access to the pin but do allow you to install a resistor at R5 and R1 as well as a pot at R2 to give you an adjustable voltage. If you would desire, you could fly-wire the WCT to the R5 resistor pads. There is no way to internally route the WCT voltage to the RLDREF pin but you can use the RLD_SENS bits to average and derive your RLD voltage. This would essentially do the same thing as routing the WCT back in to the RLDREF. I imagine your goal is to help with the CMR using the average of your input signal similar to what is described here -
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