Datasheet

CM + 1/2 V
REF
+1/2 V
REF
- V
REF
1/2
Single-Ended Inputs
t
INP
CM Voltage
CM V-
REF
1/2
CM + 1/2 V
REF
Differential Inputs
t
INP
INN
CM Voltage
CM 1/2 V
REF
-
+V
REF
-V
REF
Common-Mode Voltage (Differential Mode) =
2
, Common-Mode Voltage (Single-Ended Mode) = INN.
INN = CM Voltage
Input Range (Differential Mode) = (AINP AINN) = V ( V ) = 2 V .-
REF REF
- -
REF
(INP) + (INN)
Device
- V to
+1/2 V
1/2
REF
REF
Common
Voltage
Single-Ended Input
Device
V
peak-to-peak
REF
V
peak-to-peak
REF
Common
Voltage
Differential Input
ADS1299
SBAS499A –JULY 2012–REVISED AUGUST 2012 www.ti.com
Auxiliary Single-Ended Input
The BIASIN pin is primarily used for routing the bias signal to any electrodes in case the bias electrode falls off.
However, the BIASIN pin can be used as a multiple single-ended input channel. The signal at the BIASIN pin can
be measured with respect to the voltage at the BIASREF pin using any of the eight channels. This measurement
is done by setting the channel multiplexer setting to '010' and the BIAS_MEAS bit of the CONFIG3 register to '1'.
ANALOG INPUT
The ADS1299 analog input is fully differential. Assuming PGA = 1, the input (INP – INN) can span between
–V
REF
to +V
REF
. Refer to Table 7 for an explanation of the correlation between the analog input and digital codes.
There are two general methods of driving the ADS1299 analog input: single-ended or differential (as shown in
Figure 21 and Figure 22, respectively). Note that INP and INN are 180°C out-of-phase in the differential input
method. When the input is single-ended, the INN input is held at the common-mode voltage, preferably at mid-
supply. The INP input swings around the same common voltage and the peak-to-peak amplitude is (common-
mode + 1/2 V
REF
) and (common-mode – 1/2 V
REF
). When the input is differential, the common-mode is given by
[(INP + INN) / 2]. Both INP and INN inputs swing from (common-mode + 1/2 V
REF
) to (common-mode – 1/2
V
REF
). For optimal performance, the ADS1299 is recommended to be used in a differential configuration.
Figure 21. Methods of Driving the ADS1299: Single-Ended or Differential
Figure 22. Using the ADS1299 in Single-Ended and Differential Input Modes
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