Other Parts Discussed in Thread: ADS1299, , OPA376, , OPA333
Tool/software:
Dear Sir/Madam,
I want to use the ADS1292 for an EEG/EOG wearable application. I used the ADS1299 before, and that one worked well, but it consumes too much power and take up too much space of my PCB so I'm considering the ADS1292 instead, especially since I only need 2 EEG/EOG channels.
The ADS1292 has lower CMRR and SNR so I will need a preamplifier for it. Based on the online posts on TI forums, it seems that OPA376 is a good candidate. However, with the schematic that I attached here, the board could capture the sinewave of magnitude of 100uV, but when I attached the electrodes to it and to myself to measure the EOG, the output (through SPI) just saturated to AVDD. For the EOG measurement, I connected the Bias electrode to the RLDOUT net.
My AVDD = 5V, DVDD = 1.8V, AVSS = DGND = 0V.
My register settings (only turn Channel 1 on, Channel 2 is turned off):
- CONFIG1 = 0x00
- CONFIG2 = 0xB0 = 10110000
- LOFF = 0x10 = 00010000
- CH1SET = 0x60 = 01100000 // Gain 12
- CH2SET = 0x81 = 10000000 // Power down Ch2, input shorted
- RLD_SENS = 0x20 = 00100000 // Enable RLD buffer, not connect RLD to any inputs
- LOFF_SENS = 0x00
- LOFF_STAT = 0x00 // Ignored since LOFF_SENS is set to 0
- RESP1 = 0x02 // Value must be written if not ADS1292R
- RESP2 = 0x03 // RLDREF signal (AVDD – AVSS) / 2 generated internally
- GPIO = 0x0F // Default: set as inputs
I am using the OPA333 as unity-gain follower to bias the inputs of OPA376s to RLDOUT (2.5V). Is that the right way?
May you let me know what can be wrong with my circuit or register settings?
Thanks,
Han