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OPERATIONAL AMPLIFIER PHE-10

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OPERATIONAL AMPLIFIER PHE-10

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    1. OPERATIONAL AMPLIFIER (PHE-10) Shubha Gokhale School of Sciences, IGNOU MARCH 30, 2007

    2. Typical Op Amp IC Packages

    3. Op Amp Pin-out connections Dual-in-Line Plastic Package

    4. Op Amp Pin-outs Metal Can

    5. WHAT IS INSIDE AN OP AMP?

    6. Phases of output signal wrt input

    7. Common Emitter Amplifier

    8. Two matched transistors form a differential amplifier

    9. Transisterized Differential Amplifier

    10. Transistorized Differential Amplifier

    11. Single Ended Differential Amplifier (commonly used in op-amps)

    12. Op Amp stages with pin-outs of IC741

    13. Op amp Comparator Open loop gain of op amp is defined as: AOL = Vo / VD where VD = VNI – VINV Open loop gain of op amp is very high (ideally infinite). Any small difference between VNI and VINV results into saturation of output voltage ±VSAT i.e. for VNI < VINV output is – VSAT and for VNI > VINV output is + VSAT Value of VSAT is limited by the supply voltage of op amp

    14. Op amp Voltage Level Detector

    15. Important features of Op Amp High open loop gain (ideally infinite) which implies that even the smallest difference between the two inputs results into saturated output voltage High input impedance (ideally infinite) implies that there is no current flowing into the input of an op amp

    16. Virtual Ground These two conditions give rise to VIRTUAL GROUND, where the voltages at both the inputs are maintained at exactly same level. To achieve this condition, a feedback circuit between the output and the inverting input terminal of the op amp is necessary. This results into many applications of op amp, which qualify it to be OPERATIONAL: adder, subtractor, multiplier, divider etc.

    17. Op amp Applications

    18. Inverting Amplifier Multiplier/Divider circuit, whose gain is decided by the values of resistors

    19. Inverting Amplifier Analysis

    20. Non-inverting Amplifier

    21. Unity Gain Amplifier (Non-inverting Buffer)

    22. Inverting Adder

    23. Subtractor

    24. Subtractor Analysis

    25. Op amp integrator

    26. Op amp Differentiator

    27. Op amp Characteristics

    28. Common Mode Rejection Ratio (CMRR) It is the ability of an op amp to reject the signal which is present at its both inputs simultaneously i.e. the common mode signal CMRR = AOL / ACM, where ACM is common mode voltage gain defined by Vout / VCM Ideally CMRR is infinite For IC 741 it is 90 dB

    29. Slew Rate Maximum rate of change of output voltage (when typically a step voltage is given at the input terminal)

    30. Slew Rate (cont…) Slew rate is caused by the finite response time of the circuit elements of an op amp It limits the highest possible frequency of operation

    31. Open Loop Gain AOL is ideally infinite In case of typical practical op amp like IC 741 it is of the order of 105 i.e. about 100 dB Input Resistance RI is ideally infinite In case of IC 741 it is 2 MO Output Resistance RO is ideally zero In case of IC 741 it is 75 O

    32. Input Offset Voltage Small voltage needed to be applied between INV and NI terminals to get zero output voltage Ideally it should be 0 V (CM operation) Output Offset Voltage Under common mode operation, output voltage should be zero, but due to mismatch is devices it is non-zero (Can be corrected by applying voltage between Pins 1 and 5 of IC 741)

    33. Summary Op amp can be used for various (mathematical) operations like addition, subtraction, multiplication, division, differentiation, integration etc. Infinite open loop gain and infinite input resistance give rise to VIRTUAL GROUND Op amp is available in a simple to use IC form which require dual supply Many other applications can be implemented using op amp

    34. ACKNOWLEDGMENT Some circuits in this presentation are based on following materials: HANDBOOK OF OPERATIONAL AMPLIFIER APPLICATIONS by Texas Instruments www.williamson-labs.com

    35. Thank you !

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