ADS1298RECG-FE Input Signals
38
SBAU181B – March 2011 – Revised Janurary 2016
Copyright © 2011–2016, Texas Instruments Incorporated
ADS1298R
The voltage used to derive the right leg drive for both the positive and negative electrodes may also be
measured with respect to (AV
DD
+ AV
SS
)/2.
4.6
Lead Derivation
The EVM is configured to generate the 12 ECG signals using 10 electrodes connected to the eight ADC
channels. Lead I, Lead II, and V1-V6 are computed in the analog domain, while the augmented leads and
Lead III are computed digitally. The channel assignments are described in
.
•
LA = Left Arm
•
LL = Left Leg
•
RA = Right Arm
(1)
WCT = (LA + RA + LL)/3
Table 2. ADS1298R Lead Measurements
ADS1298R Input Channels
Lead
(1)
1
V6 = V6 – WCT
2
LEAD I = LA – RA
3
LEAD II = LL – RA
4
V2 = V2 – WCT
5
V3 = V3 – WCT
6
V4 = V4 – WCT
7
V5 = V5 – WCT
8
V1 = V1 – WCT
Table 3. Derived Lead Calculations
Derived Lead
Formula Used to Calculate
LEAD III
LL - RA - LA = LEAD II - LEAD I
aVR
RA - (LA + LL) / 2 = - (LEAD I + LEAD II) / 2
aVL
LA - (RA +LL) / 2 = LEAD I - LEAD II / 2
aVF
LL - (RA + LA) / 2 = LEAD II - LEAD I /2
4.7
Wilson Center Terminal (WCT)
The Wilson Center Terminal voltage is internally generated by the ADS1298R device. The
WCT1
and
WCT2
registers provide controls to select any of the eight inputs (CH1P to CH4P, CH1M to CH4M) for
routing to the three integrated WCT amplifiers.
The ADS1298RECG-FE is configured for 12-lead ECG inputs, with the limb electrodes connected as
shown in
. During EVM power-up, the firmware configures the device to route CH2P, CH2M, and
CH3P (RA, LA, LL) to the internal buffers. This configuration generates a signal at the WCT pin equal to
(RA + LA + LL)/3. By installing JP16, the WCT is routed to the single-ended channels to achieve the
desired signals.
4.8
Right Leg Drive
The RL electrode is driven directly by the RLD signal generated on-chip by the ADS1298R. The bandwidth
of the RLD loop is determined by R8 (392k
Ω
) and C20 (10nF). Users can change these values to set the
bandwidth based on their specific application. The loop stability is determined by the user’s specific
system. Therefore, adjustment of the feedback component values may be required to ensure stability if
additional filtering components and long cables are added before the ADS1298RECG-FE.
In a typical application, the RLD signal is implemented as the average of RA, LA, and LL. For system
flexibility, the ADS1298R allows the user to select any combination of the electrodes to generate the RLD
(see
for more details).