1. Operational Amplifiers Hunter Greene Wendy Siemens 20 February 2006

2. Operational Amplifier Outline Introduction Characteristics Idealizations Cautions Applications References

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

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

5. Characteristics Open Loop Operation If V 1 >V 2, V out =+15V If V 1 <V 2, V out =-15V If V 1 =V 2, V out =0V Typical op-amps swing from V + to V - with mV input voltage differences +15V -15V V out V1V1 V2V2

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 + =V in and V - =V + R 1 /V in =R 2 /(V out -V in ) V in /V out =(R 1 +R 2 )/R 1 => Non-inverting Amplifier

8. 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 V+V+ V-V- V out V1V1 V2V2

9. Idealizations Ideal Op-AmpTypical Op-Amp Input Resistanceinfinity 10 6  (bipolar) 10 9  - 10 12  (FET) Input Current010 -12 – 10 -8 A Output Resistance0 100 – 1000  Operational Gaininfinity10 5 - 10 9 Common Mode Gain010 -5 BandwidthinfinityAttenuates and phases at high frequencies (depends on slew rate) TemperatureindependentBandwidth and gain 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. R 1 = R 2 = R F V out = -(V 1 +V 2 ) Applications

14. Integrator Circuit Applications

17. 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_amplifierhttp://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