Datasheet

Wcta
8:1MUX
WCT1[2:0]
IN4N
IN4P
IN3N
IN3P
IN2N
IN2P
IN7N
IN7P
IN6N
IN6P
IN5N
IN5P
IN1N
IN1P
Wctb
8:1MUX
WCT2[5:3]
Wctc
8:1MUX
WCT2[2:0]
ToChannel
PGAs
ADS1198
avF_ch6 avF_ch5 avF_ch7
avF_ch4
ToChannel
PGAs
ADS1194, ADS1196
ADS1198
SBAS471C –APRIL 2010– REVISED NOVEMBER 2011 www.ti.com
As mentioned previously in this section, all three WCT amplifiers can be connected to one of the eight analog
input pins. The inputs of the amplifiers are chopped and the chopping frequency is at 8kHz. The chop frequency
shows itself at the output of the WCT amplifiers as a small square-wave riding on dc. The amplitude of the
square-wave is the offset of the amplifier and is typically 5mV
PP
. This artifact as a result of the chopping function
is out-of-band and thus does not interfere with ECG-related measurements. Note that if the output of a channel
connected to the WCT (for example, V
LEAD
channels) is connected to one of the pace amplifiers for external pace
detection, the artifact of chopping appears at the Pace amplifier output.
Augmented Leads
In the typical implementation of the 12-lead ECG with eight channels, the augmented leads are calculated
digitally. In certain applications, it may be required that all leads be derived in analog rather than digital. The
ADS1198 provides the option to generate the augmented leads by routing appropriate averages to channels 5 to
7. The same three amplifiers that are used to generate the WCT signal are used to generate the Goldberger
terminal signals as well. Figure 45 shows an example of generating the augmented leads in analog domain. Note
that in this implementation it takes more than eight channels to generate the standard 12 leads. Also, this feature
is not available in the ADS1196 and ADS1194.
Figure 45. Analog Domain Augmented Leads
Right Leg Drive with the WCT Point
In certain applications, the out-of-phase version of the WCT is used as the right leg drive reference. The
ADS1198 provides the option to have a buffered version of the WCT terminal at the RLD_OUT pin. This signal
can be inverted in phase using an external amplifier and used as the right leg drive. Refer to the Right Leg Drive
(RLD DC Bias Circuit) section for more details.
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Product Folder Link(s): ADS1194 ADS1196 ADS1198