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Operational Amplifiers

This comprehensive guide explores the characteristics, idealizations, and applications of operational amplifiers. Learn about key concepts such as open and closed loop operations, idealizations, and cautionary measures. Discover how operational amplifiers are used in integrator circuits, position/velocity measurement, and microphone/speaker amplification. Gain insights into their cost-saving capabilities and the importance of negative feedback for proper operation. Explore valuable references for further information on operational amplifiers.

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Operational Amplifiers

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  1. Operational Amplifiers Hunter Greene Wendy Siemens 20 February 2006

  2. Operational Amplifier • Outline • Introduction • Characteristics • Idealizations • Cautions • Applications • References

  3. V+ V- Introduction • Performs operations on input voltages • Active component • V+ and V- power • Can amplify inputs

  4. V+ V- Characteristics • Symbol • Positive-going input • Negative-going input • Open loop operation: a very small difference between +Vin and -Vin swings the output voltage to the corresponding Vref (V+ or V-)

  5. +15V V1 Vout V2 -15V Characteristics • Open Loop Operation • If V1>V2, Vout=+15V • If V1<V2, Vout=-15V • If V1=V2, Vout=0V • Typical op-amps swing from V+ to V- with mV input voltage differences

  6. Characteristics • Closed Loop Operation • Golden Rule 1: The output attempts to make the input voltage difference zero. • Golden Rule 2: The inputs draw no current.

  7. Characteristics • V+=Vin and V-=V+ • R1/Vin=R2/(Vout-Vin) • Vin/Vout=(R1+R2)/R1 => Non-inverting Amplifier

  8. V+ V1 Vout V2 V- Idealizations • Infinite open loop gain • Infinite bandwidth • Infinite input impedances (zero input current) • Zero output impedance • Zero noise • Zero input offset voltage • Zero temperature dependence

  9. Idealizations http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/opampcon.html#c1

  10. Cautions • Cautions: • Active regions: clipping occurs when the output saturates • Inputs: feedback must be negative for proper operation • Input difference limits: ignoring limits on input differences cause harmful current levels.

  11. Applications • Cheaper than buying a commercial PID controller. • Saves microcontroller processing time

  12. Applications R1 = R2 = RF Vout= -(V1+V2)

  13. Applications

  14. Applications Integrator Circuit

  15. Applications

  16. Applications

  17. Applications • Positions/velocity measurement • The output signal from an accelerometer can be integrated once to give a voltage output proportional to velocity. • This signal can then be integrated again to give a voltage proportional to position. • This can be much cheaper than other position measuring devices such as LVDT’s which can range from $70-$300.

  18. Applications • Microphone/Speaker Amplification • A non-inverting amplifier is typically used to amplify the small signals from microphones before the sound can be processed. • Computer sound systems must amplify the signals from Digital-to-Analog converters before sending the sound signal to the speakers.

  19. References • For further information: • Wikipedia: http://en.wikipedia.org/wiki/Operational_amplifier • The Art of Electronics, Horowitz and Hill • Introduction to Mechatronics and Measurement Systems, Alciatore and Histand • Electrical Engineering, Hambley • ME 3056 and 4053 lab manual appendices show details of op-amp circuits used in data acquisition

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