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Winter 2011. UCSD: Physics 121; 2011. 2. Operation Amp Introduction. Operation amps (intensifiers/cradles when all is said in done) are drawn as a triangle in a circuit schematicThere are two inputsinverting and non-invertingAnd one outputAlso power associations (take note of no unequivocal ground). . . 2. 3. 4. 7. 6. divot on pin-1 end.

Transcripts

Operational Amplifiers Magic Rules Application Examples

UCSD: Physics 121; 2012 + Op-Amp Introduction Op-amps (intensifiers/cushions all in all) are drawn as a triangle in a circuit schematic There are two sources of info rearranging and non-altering And one yield Also control associations (take note of no express ground) divot on pin-1 end V + 7 2 transforming input 6 yield non-reversing input 3 4 V

UCSD: Physics 121; 2012 The perfect operation amp Infinite voltage pick up a voltage distinction at the two information sources is amplified interminably in truth, something like 200,000 means contrast between + terminal and terminal is opened up by 200,000! Endless info impedance no present streams into contributions to truth, around 10 12 for FET input operation amps Zero yield impedance rock-strong autonomous of burden generally valid up to current most extreme (normally 5–25 mA) Infinitely quick (endless transfer speed) in truth, constrained to few MHz range slew rate restricted to 0.5–20 V/s

UCSD: Physics 121; 2012 + Op-amp without criticism The inner operation amp recipe is: V out = pick up ( V + V ) So if V + is more noteworthy than V , the yield goes positive If V is more prominent than V + , the yield goes negative An increase of 200,000 makes this gadget (as outlined here) for all intents and purposes futile V V out V +

UCSD: Physics 121; 2012 + Infinite Gain in negative input Infinite addition would be pointless aside from in the self-managed negative input administration negative criticism appears to be terrible, and positive great—however in hardware positive input implies runaway or wavering, and negative input prompts soundness Imagine snaring the yield to the altering terminal: If the yield is not as much as V in , it shoots positive If the yield is more prominent than V in , it shoots negative result is that yield rapidly compels itself to be precisely V in negative input circle V in

UCSD: Physics 121; 2012 + Even under burden Even in the event that we stack the yield (which as envisioned needs to drag the yield to ground)… the operation amp will do all that it can inside its present confinements to drive the yield until the modifying input achieves V in negative input makes it self-revising for this situation, the operation amp drives (or pulls, if V in is negative) a current through the heap until the yield meets V in so what we have here is a support : can apply V into a heap without troubling the wellspring of V in with any present! Critical note : operation amp yield terminal sources/sinks current voluntarily dislike inputs that have no present stream V in

UCSD: Physics 121; 2012 + Positive criticism pathology In the setup beneath, if the + information is even a smidge higher than V in , the yield goes way positive This makes the + terminal much more positive than V in , exacerbating things This framework will instantly " rail " at the supply voltage could rail either heading, contingent upon introductory counterbalance V in positive input: BAD

UCSD: Physics 121; 2012 Op-Amp " Golden Rules " When an operation amp is designed in any negative-criticism course of action, it will comply with the accompanying two principles: The contributions to the operation amp draw or source no present (genuine whether negative criticism or not) The operation amp yield will do whatever it can (inside its impediments) to have the voltage effect between the two data sources zero

UCSD: Physics 121; 2012 + Inverting speaker illustration R 2 Applying the standards: terminal at " virtual ground " so present through R 1 is I f = V in/R 1 Current does not stream into operation amp (one of our guidelines) so the current through R 1 must experience R 2 voltage drop crosswise over R 2 is then I f R 2 = V in ( R 2/R 1 ) So V out = 0 V in ( R 2/R 1 ) = V in ( R 2/R 1 ) Thus we open up V in by element R 2/R 1 negative sign procures title "modifying" enhancer Current is drawn into operation amp yield terminal R 1 V in V out

UCSD: Physics 121; 2012 + Non-upsetting Amplifier R 2 Now neg. terminal held at V in so present through R 1 is I f = V in/R 1 (to left, into ground) This current can\'t originate from operation amp input so comes through R 2 (conveyed from operation amp yield) voltage drop crosswise over R 2 is I f R 2 = V in ( R 2/R 1 ) with the goal that yield is higher than neg. input terminal by V in ( R 2/R 1 ) V out = V in + V in ( R 2/R 1 ) = V in (1 + R 2/R 1 ) along these lines increase is (1 + R 2/R 1 ) , and is sure Current is sourced from operation amp yield in this case R 1 V out V in

UCSD: Physics 121; 2012 + Summing Amplifier R f R 1 Much like the altering enhancer, yet with two info voltages modifying input still held at virtual ground I 1 and I 2 are included to gone through R f so we get the (rearranged) entirety: V out = R f ( V 1/R 1 + V 2/R 2 ) if R 2 = R 1 , we get a whole relative to ( V 1 + V 2 ) Can have any number of summing information sources we\'ll make our D/A converter thusly V 1 R 2 V out V 2

UCSD: Physics 121; 2012 + Differencing Amplifier R 2 The non-upsetting info is a straightforward voltage divider: V hub = V + R 2/( R 1 + R 2 ) So I f = ( V V hub )/R 1 V out = V hub I f R 2 = V + (1 + R 2/R 1 )( R 2/( R 1 + R 2 )) V ( R 2/R 1 ) so V out = ( R 2/R 1 )( V V ) in this manner we contrast V and V R 1 V V out V + R 1 R 2

UCSD: Physics 121; 2012 + Differentiator (high-pass) R For a capacitor, Q = CV , so I top = dQ/dt = C·dV/dt Thus V out = I top R = RC · dV/dt So we have a differentiator, or high-pass channel if sign is V 0 sin t , V out = V 0 RC cos t the - reliance implies higher frequencies opened up more C V in V out

UCSD: Physics 121; 2012 + Low-pass channel (integrator) C I f = V in/R, so C·dV top/dt = V in/R and since left half of capacitor is at virtual ground: dV out/dt = V in/RC so and hence we have an integrator (low pass) R V in V out

UCSD: Physics 121; 2012 RTD Readout Scheme

UCSD: Physics 121; 2012 Notes on RTD readout RTD has resistance R = 1000 + 3.85 T (C) Goal: put 1.00 mA crosswise over RTD and present yield voltage corresponding to temperature: V out = V 0 + T First stage: put exactness 10.00 V reference crosswise over accuracy 10k resistor to make 1.00 mA, sending crosswise over RTD yield is 1 V at 0C; 1.385 V at 100C Second stage: resistor system produces 0.25 mA of source through R9 R6 gulps 0.25 mA when stage 1 yield is 1 V so no current through criticism yield is zero volts At 100 C, R6 guzzles 0.346 mA, leaving net 0.096 that must come through criticism If R7 + R8 = 10389 ohms, yield is 1.0 V at 100 C Tuning resistors R11, R7 permits control over balance and pick up, separately: this config set up for V out = 0.01 T

UCSD: Physics 121; 2012 Hiding Distortion Consider the "push-pull" transistor course of action to the privilege a npn transistor (top) and a pnp (bot) weak info can drive enormous burden (speaker?) base-emitter voltage varies by 0.6V in every transistor (emitter has bolt) input must be higher than ~0.6 V for the npn to end up dynamic information must be lower than 0.6 V for the pnp to be dynamic There is a dead zone in the middle of where neither one of the transistors conducts, so one would get " hybrid contortion " yield is zero while input sign is amongst 0.6 and 0.6 V + out in V hybrid twisting

UCSD: Physics 121; 2012 + Stick it in the input circle! V + By staying the push-maneuver into an operation amp\'s criticism circle, we promise that the yield loyally takes after the information! all things considered, the brilliant guideline requests that + input = input Op-amp jerks up to 0.6 and down to 0.6 at the hybrid it\'s practically enchantment : it makes sense of the fancies/nonlinearities of the thing on top of it Now get points of interest of push-draw drive ability, without the wreckage out V in V info and yield now the same

UCSD: Physics 121; 2012 + Dogs in the Feedback The operation amp is committed to create the converse canine so that a definitive yield might be as clean as the information. Lesson: you can cover up frightful nonlinearities in the criticism circle and the operation amp will " make the best decision " "there is no pooch" V in puppy opposite canine We owe on account of Hayes & Horowitz, p. 173 of the understudy manual friend to the Art of Electronics for this extremely valuable allegory.

UCSD: Physics 121; 2012 Reading Read 6.4.2, 6.4.3 Pay extraordinary consideration regarding Figure 6.66 (6.59 in 3 rd ed.)