ECG Acquisition in a Computer - ECG Acquisition and Automated Remote Processing - page 58

D

T 2

T 1

Fig. 3.4 Optical isolation circuit using LOC 110

modulated signal is converted back to analog voltage by an averaging technique.
The functional block diagram of a capacitive IsoA is shown in Fig. 3.5 . However,
in capacitive isolation also, the use of separate isolated power supply is mandatory.
In some variants of capacitive IsoA, the input is modulated to a duty cycle encoded
signal (Burr-Brown ISO103, ISO107, ISO121), while in others, it is converted to
frequency (Burr-Brown ISO102, ISO106).
The performance of an isolation amplifier is described by isolation-mode
rejection ratio (IMRR), which refers to its ability to suppress the feed-through
isolation-mode voltage that arises across the barrier and output stage, detailed
in [ 24 ].
Accidental voltage surge protection from the biomedical equipment can be
achieved by connecting voltage-limiting devices (e.g., zener diode) between the
connecting electrode and ground. The device absorbs the extra current inrush when
the voltage across it raises a certain value, typically 300 mV or higher.

Fig. 3.5 Block diagram of capacitive isolation amplifier