Datasheet

ADAS1000-3/ADAS1000-4 Data Sheet
Rev. A | Page 28 of 76
ELECTRODE/LEAD FORMATION AND INPUT
STAGE CONFIGURATION
The input stage of the ADAS1000-3/ADAS1000-4 can be
arranged in several different manners. The input amplifiers
are differential amplifiers and can be configured to generate
the leads in the analog domain, before the ADCs. In addition
to this, the digital data can be configured to provide either
electrode or lead format under user control as described in
Table 36. This allows maximum flexibility of the input stage
for a variety of applications.
Analog Lead Configuration and Calculation
Leads are configured in the analog input stage when CHCONFIG
= 1, as shown in Figure 55. This uses a traditional in-amp
structure where lead formation is performed prior to digitiza-
tion, with WCT created using the common-mode amplifier.
While this results in the inversion of Lead II in the analog
domain, this is digitally corrected so output data have the
proper polarity.
Digital Lead Configuration and Calculation
When the ADAS1000-3/ADAS1000-4 are configured for digital
lead mode (see the FRMCTL register, 0x0A[4], Table 36), the
digital core will calculate each lead from the electrode signals.
This is straightforward for Lead I/ Lead II/Lead III. Digital lead
calculation is only available in 2 kHz and 16 kHz data rates.
Single-Ended Input Electrode
In this mode, the electrode data are digitized relative to the
common-mode signal, VCM, which can be arranged to be any
combination of the contributing ECG electrodes. Common-
mode generation is controlled by the CMREFCTL register
as described in Table 31.
Common Electrode Configuration
In this mode, all electrodes are digitized relative to a common
electrode (CE), for example, RA. This arrangement enables input
on four electrode paths, ECG1, ECG2, ECG3, and CM_IN.
Standard leads must be calculated by post processing the output
data of the ADAS1000-3/ADAS1000-4. See Figure 57.
Table 11. Electrode and Lead Configurations
0x0A
[4]
1
0x01
[10]
2
0x05
[8]
3
Mode Word1 Word2 Word3
0 0 0 Single-ended input, digitally calculated leads Lead I
(LA − RA)
Lead II
(LL − RA)
Lead III
(LL − LA)
0 0 1 Common electrode (CE) leads (here RA electrode is
connected to the CE electrode (CM_IN) and V1 is on
ECG3 input)
4
Lead I
(LA − RA)
Lead II
(LL − RA)
V1’
((V1 − RA) − (LA − RA) − (LL − RA))/3
0 1 0 Analog leads
5
Lead I
(LA − RA)
Lead II
(LL − RA)
Lead III
(LL − LA)
1 0 0 Single-ended input electrode relative to VCM
6
LA − VCM LL − VCM RA − VCM
1 0 1
Leads formed relative to a common electrode (CE
4
)
LA − CE LL − CE V1 − CE
1
Register FRMCTL, Bit DATAFMT: 0 = digital lead/vector format; 1 = electrode format.
2
Register ECGCTL, Bit CHCONFIG: 0 = single-ended input (digital lead mode or electrode mode); 1 = differential input (analog lead mode).
3
Register CMREFCTL, Bit CEREFEN: 0 = CE disabled; 1 = CE enabled.
4
Common electrode mode as shown in Figure 57.
5
Analog lead mode as shown in Figure 55.
6
Single-ended input electrode mode as shown in Figure 56.