3/26 10.2.2 Instrumentation Amplifiers -Isolation amplifiers A special subclass of instrumentation amplifiers; General Applications: low-level signals ride on top of high common-mode voltages; Possibilities exist of troublesome ground disturbances and ground loops; Processing circuitry must be protected from faults and power transients; Interference from motors,power lines is heavy; Patient protection is important in biomedical applications. Isolation Techniques:transformer coupling and optical coupling. Two-port Isolator:Signal input isolated from signal output and power input circuits. Three-port Isolator:In addition to two-port isolator,signal output is isolated from power input circuits. 4/26 10.2.2 Instrumentation Amplifiers-Isolation amplifiers Thermocouple Instrumentation amplifier Load Connection required for bias current return Isolation Hi amplifier Hi Gain Lo Load Fig 10.11 Instrumentation/lsolation Amplifier Comparison Advantages compared to other IA:it does not require a ground connection for input signal,so the signal is isolated from ground and the rejection of interfering noise may be much improved.‹ A special subclass of instrumentation amplifiers; ‹ General Applications: z low-level signals ride on top of high common-mode voltages; z Possibilities exist of troublesome ground disturbances and ground loops; z Processing circuitry must be protected from faults and power transients; z Interference from motors, power lines is heavy; z Patient protection is important in biomedical applications. ‹ Isolation Techniques: transformer coupling and optical coupling. ‹ Two-port Isolator: Signal input isolated from signal output and power input circuits. ‹ Three-port Isolator: In addition to two-port isolator, signal output is isolated from power input circuits. 10.2.2 Instrumentation Amplifiers - Isolation amplifiers13/26 Fig 10.11 Instrumentation/Isolation Amplifier Comparison ‹ Advantages compared to other IA: it does not require a ground connection for input signal, so the signal is isolated from ground and the rejection of interfering noise may be much improved. 10.2.2 Instrumentation Amplifiers - Isolation amplifiers14/26