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Operational Amplifiers

Operational Amplifiers. Instructor: Chia-Ming Tsai Electronics Engineering National Chiao Tung University Hsinchu, Taiwan, R.O.C. Contents. Introduction Operational Amplifiers (OP AMPs) Ideal OP AMP Inverting AMP Noninverting AMP Summing AMP Difference AMP Cascaded OP AMP Circuits

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Operational Amplifiers

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  1. Operational Amplifiers Instructor: Chia-Ming Tsai Electronics Engineering National Chiao Tung University Hsinchu, Taiwan, R.O.C.

  2. Contents • Introduction • Operational Amplifiers (OP AMPs) • Ideal OP AMP • Inverting AMP • Noninverting AMP • Summing AMP • Difference AMP • Cascaded OP AMP Circuits • Applications

  3. Introduction • The op amp is a basic building block for performing mathematical operations such as summation, amplification, integration, and differentiation • The concept of virtual short between the differential inputs of the op amp is extremely important for circuit analysis

  4. OP AMPs • Complex circuit networks consisting of transistors, resistors, capacitors, and diodes

  5. _ + Cont’d Equivalent circuit of an op amp

  6. Slope = A Cont’d

  7. Example

  8.   Ideal OP AMP • Infinite open-loop voltage gain: A  • Infinite input resistance: Ri  • Zero output resistance: Ro 0 • v1 = v2 (virtual short) assumed for analysis

  9. (feedback resistor) Inverting AMP The equivalent circuit

  10. i1 i2 a i3 Example: I-to-V Converters

  11. Noninverting AMP

  12. Voltage Follower • Conditions: Rf= 0 or R1=  or both • Unity gain: Av= 1 • Useful as a buffer amp due to its very high Ri and very low Ro

  13. Summing AMP

  14. Difference AMP

  15. Cascaded OP AMP Circuits

  16. Applications: DAC Digital-to-Analog Converter (DAC) MSB: most significant bit LSB: least significant bit

  17. Applications:Instrumentation Amplifier (IA)

  18. Cont’d • Characteristics of IA • Voltage gain adjustable by RG • Very high Ri and very low Ro • The differential voltage is amplified and the common-mode voltage is rejected

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