Golden Rules

Proceedings of the 24 th International Modal Analysis Conference (IMAC XXIV), St. Louis, MO, January 30 - February 2,

Image credit: ITIT V out = A(V in+ - V in- ) A ~ 10I T R 2 A is the “open loop” voltage gain V in+ I1I1 I2I2

t (sec) Given: +/- V cc = +/- 15 V Vs = 5 V, R1 = 4 k  R2 = 1 k  Solve: For the input signal shown below, sketch v out (t) v in (t) V

Given: +/- V cc = +/- 15 V Vs = 5 V, R1 = 4 k  R2 = 1 k  Solve: For the input signal shown below, sketch v out (t) t (sec) Comparator: v - = 1V. Pos. saturation occurs whenever v in (t) > 1V, Neg. sat. otherwise

Op amp in the smoke detector

 IF connected in negative feedback, an op-amp circuit obeys the following 2 golden rules:  Golden Rule #1: v + = v -  Golden Rule #2 i + = i - = 0 r.com/offtheclock/index.php/archives/2166

Given: +/- V cc = +/- 15 V R f = 4 k  R i = 1 k  R 3 = 800  Solve: For the input signal shown below (1V amplitude cosine), sketch v out (t) Non-inverting amplifier, G = (1+R f /R i ) = 5;

Given: +/- V cc = +/- 15 V R f = 4 k  R i = 1 k  R 3 = 800  Solve: For the input signal shown below (5V amplitude cosine), sketch v out (t) Non-inverting amplifier, G = (1+R f /R i ) = 5; Saturation occurs!

 IF connected in negative feedback, an op-amp circuit obeys the following 2 golden rules:  Golden Rule #1: v + = v -  Golden Rule #2 i + = i - = 0 r.com/offtheclock/index.php/archives/2166

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Audio mixer Weights for weighted sum

But Buzz manages to mess things up by firing his rockets, right as the chosen alien offers parting words of solace Noise canceling headphones would help. Design them for the aliens.

 Design an op-amp based circuit that acts as a noise canceling headphone.

Isolates high R s from low R L Use it anytime you want to get a voltage measurement without disturbing the circuit you are trying to measure

(A) Inverting amp (B) Summer (C) Non-inverting amp (D) Buffer (E) Comparator

Instrumentation Amp & Active Filters

implications Skin electrodes Filters and Amplifiers

Instrumentation Amplifier: What’s Inside the Box Difference Amplifier

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Raw signal of muscle contraction measured on the skin: 0.1 – 1 mV in amplitude Frequencies of interest are Hz. Lots of other sources of noise outside this frequency band. Design a system that : Outputs ~5V amplitude when muscle contracts Contains frequency content (potentially) related to muscle contractions only.

Skin conductance vs. time