Digital techniques for optical isolation
The document discusses different types of isolation amplifiers, which provide electrical isolation and safety barriers between input and output circuits. There are three main types: transformer coupling uses a transformer to couple supplies; optical isolation converts signals to light; and capacitive coupling uses a differential capacitive barrier and separate supplies. Transformer coupling is commonly used and offers medium isolation voltage and gain stability. Optical isolation provides low-cost isolation but lower voltage ratings. Capacitive coupling has the highest isolation resistance and gain stability but also the highest cost. Isolation amplifiers have applications in medical equipment, industrial processes, and other areas requiring electrical isolation.
Digital techniques for optical isolation
- 2. Isolation amplifiers provide electrical isolation and an electrical safety barrier. They protect the patients from leakage currents. 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.
- 3. GENERAL PIN CONFIGURATION OF ISOLATION AMPLIFIER
- 4. TYPES Three types of methods are used to design isolation amplifier Transformer isolation Optical isolation Capacitive isolation
- 6. 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 isolated stages. Rectifier- input to primary OPAMP. Transformer- couples the supply. Oscillator – input to secondary OPAMP. A low pass filter is used to remove the other frequency components.
- 7. Advantages High common mode rejection ratio High linearity High accuracy
- 9. applications MEDICAL Patient Monitoring and Diagnostic Instrumentation INDUSTRIAL Ground Loop Elimination and Off-ground Signal Measurement NUCLEAR Input/output/Power Isolation
- 11. The 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 circuit. Each circuit is battery driven. The input circuit converts the signal to light and the output circuit converts the light back to signal.
- 13. advantages Original frequency and amplitude is obtained. High linearity. No modulator or demodulator is needed as it couples optically. Improves patient safety
- 14. Application INDUSTRIAL PROCESS CONTROL DATAACQUISITION INTERFACE ELEMENT BIOMEDICAL MEASUREMENTS PATIENT MONITORING TEST EQUIPMENT CURRENT SHUNT MEASUREMENT GROUND-LOOP ELIMINATION SCR CONTROLS
- 16. It uses digital encoding of the input voltage and frequency modulation. 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 barrier. Separate supplies are given for both sides.
- 18. advantages Ripple noises are removed. It avoids device noise, radiated noise and conducted noise. High immunity to magnetic noises. Useful for analog systems. Has high gain stability and linearity.
- 19. applications DATAACQUISITION INTERFACE ELEMENT PATIENT MONITORING ECG EEG
- 20. Comparative study Commonly used Transformer isolation amplifier Cost Optical- low cost due to less components Transformer Capacitor coupled- high cost Isolation voltage Optical- low (800V) Transformer- medium (1200V)
- 21. Isolation resistance Optical- 10^12 Transformer- 10^10 Capacitance- 10^12 Gain stability and Linearity Optical- 0.02% Transformer- between 0.005% and 0.02% Capacitance- 0.005% (best)
- 23. ANGULAR VIEWS
- 24. VCG WAVEFORM