Other Parts Discussed in Thread: ADS1298
Hello,
I'm using the ADS1298 for a 12 lead electrocardiograph, it seems to be working fine, but I'm having some problems with the PACE_OUT1 and PACE_OUT2 signals. according to the datasheet (page 64)
"Two of the eight channels can be selected using register bits in the PACE register, one from the odd-numbered channels and the other from the even-numbered channels. During the differential to single-ended conversion, there is an attenuation of 0.4. Therefore, the total gain in the pace path is equal to (0.4 × PGA_GAIN)."
But the signal I'm getting from PACE_OUT1 and PACE_OUT2 is the same voltage amplitude with all the different PGA_GAIN configuration. It seems to be fixed at about 5.
We have made same test in your evaluation board "ADS1298ECG FE-PDK" and in our custom solution with the same results.
We are using internal 2.4V voltage reference, and this is our register configuration.
| Register | Address | Value | D7 | D6 | D5 | D4 | D3 | D2 | D1 | D0 |
| ID | 0x00 | 0x92 | 1 | 0 | 0 | 1 | 0 | 0 | 1 | 0 |
| CONFIG1 | 0x01 | 0x86 | 1 | 0 | 0 | 0 | 0 | 1 | 1 | 0 |
| CONFIG2 | 0x02 | 0x10 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 |
| CONFIG3 | 0x03 | 0xDC | 1 | 1 | 0 | 1 | 1 | 1 | 0 | 0 |
| LOFF | 0x04 | 0x03 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 |
| CH1SET | 0x05 | 0x00 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| CH2SET | 0x06 | 0x00 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| CH3SET | 0x07 | 0x00 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| CH4SET | 0x08 | 0x00 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| CH5SET | 0x09 | 0x00 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| CH6SET | 0x0A | 0x00 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| CH7SET | 0x0B | 0x00 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| CH8SET | 0x0C | 0x00 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| RLD_SENSP | 0x0D | 0x00 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| RLD_SENSN | 0x0E | 0x00 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| LOFF_SENSP | 0x0F | 0xFF | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| LOFF_SENSN | 0x10 | 0x02 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 |
| LOFF_FLIP | 0x11 | 0x00 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| LOFF_STATP | 0x12 | 0x00 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| LOFF_STATN | 0x13 | 0xFF | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| GPIO | 0x14 | 0x00 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| PACE | 0x15 | 0x08 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 |
| RESP | 0x16 | 0x00 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| CONFIG4 | 0x17 | 0x02 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 |
| WCT1 | 0x18 | 0x0A | 0 | 0 | 0 | 0 | 1 | 0 | 1 | 0 |
| WCT2 | 0x19 | 0xE3 | 1 | 1 | 1 | 0 | 0 | 0 | 1 | 1 |
The actual question is, what is the gain that I should expect in the PACE_OUT1 signal? Is the PACE_OUT1 gain fixed or it depends on the PGA gain as the datasheet says? I there something wrong with the above configuration?
Thank you very much in advance.
