ads1192 output data format

Hey Min,

1. Those values do look correct for the case of shorted inputs. Since the data is output in 2's complement format, those values correspond to very small negative numbers.

2. You are correct. To get the right sign on the output data, you will need to use a signed integer data type.

3. What do you mean by lead 1 configuration? Are you talking about using 2 electrodes without the right leg electrode?

Regards,
Brian Pisani

Hey Min,

It is possible! The only you thing you must account for is the common mode drift on the body and how it relates to the supplies of the ADC. You'll have to find a way to AC couple the inputs such that the measurement its not affected by the DC common mode of the body. With the Right Leg Drive, the common mode will be set by the chip, so without it you'll have to set the common mode another way. One of the most popular and easy ways to do that is to use a DC blocking capacitor followed by a voltage divider to set the new input common mode to mid-supply. There is (sort of) and example of this in the EVM schematic for this device: www.ti.com/.../slau384a.pdf

If you look at the channel 1 inputs, you'll notice a few series capacitors. Some of that circuitry is only used for the ADS1292R respiration. I would like you to take a look at C49, C50, R66, R72, R64, and R62. These passive components AC couple the inputs. The capacitor will block the DC from the body and the resistors bias the inputs at mid-supply. Let me know if you need me to explain that further.

For the digital code to output voltage translation, you would simply multiply your output code by the LSB size. The LSB size is given as Vref/(2^15-1). In addition, if you used the internal PGA on the device to gain your signal before converting it, you'll have to divide by your gain to get the original signal. To maintain the sign, I'd recommend storing the value you get as a signed integer. I'm not sure whether you'll have to write some code to cleverly do it or if your compiler is capable of simply casting a uint16_1 to an int16_t (though some may argue that casting is poorly written code).

Regards,
Brian Pisani