amplifiers provide electrical isolation
and an electrical safety barrier.
They protect the patients from leakage
They break the ohmic continuity of electrical
signals between input and output.
Isolated power supplies are provided for both
the input and output stages.
Used to amplify low level signals.
Three types of methods are used to design isolation
It uses either frequency modulated or a pulse
width modulated carrier signal.
Internally it has 20KHz oscillator, transformer,
rectifier and filter to provide supplies for each
Rectifier- input to primary OPAMP.
Transformer- couples the supply.
Oscillator – input to secondary OPAMP.
A low pass filter is used to remove the other
High common mode rejection ratio
Patient Monitoring and Diagnostic
Ground Loop Elimination and
Off-ground Signal Measurement
biological signal is converted into a light
signal by LED for further process.
It has patient circuit which is the input circuit
and a phototransistor which forms the output
Each circuit is battery driven.
The input circuit converts the signal to light
and the output circuit converts the light back to
Original frequency and amplitude is obtained.
No modulator or demodulator is needed as it
Improves patient safety
CURRENT SHUNT MEASUREMENT
It uses digital encoding of the input voltage and
The input voltage is converted to proportional
charge on the switched capacitor.
It has modulator and demodulator circuits.
The signals are sent across a differential capacitive
Separate supplies are given for both sides.
Ripple noises are removed.
It avoids device noise, radiated noise and
High immunity to magnetic noises.
Useful for analog systems.
Has high gain stability and linearity.
Transformer isolation amplifier
Optical- low cost due to less components
Capacitor coupled- high cost
Optical- low (800V)
Transformer- medium (1200V)
Capacitance- high (2200V)
Gain stability and Linearity
Transformer- between 0.005% and 0.02%
Capacitance- 0.005% (best)