OP Amp

[Ideal op-amp

- Infinite input impedance

- Infinit gain for differential input

- Zero output impedance

- Infinite frequency bandwidth

- No nonlinear distortion

[Equivalent circuit of an ideal op-amp

[Biasing

[Feedback

- Almost always used with a negative feedback

- Part of the output signal is returned to the inverting input

- Feed back reduces the gain of the op-amp

[Inverting amp with higher gain

[Summing amp

[Op-amp with positive feedback

- Saturated the amp. Not a good idea.

[Non-inverting amplifier

[Voltage follower

[Voltage-to-current converter

- Transconductance amplifier

Precision 250Ω resistor. R_load doesn't matter, just as long as op-amp has high enough voltage rails.

[Matrix equations for op-amp circuits

- Use the node analysis

II. Actual op-amp

Nonideal linear operation: gain decreases with the frequency

Nonlinearity

DC offset

[Open-loop gain

f_BOL: open-loop bandwidth

[Nonlinear limitations

When voltage or current limits are exceeded, clipping of the output signal occurs causing large nonlinear distortions.

[Slew-rate limit

Full-power bandwidth:

[DC offset values

Offset in the bias current: I_B+, I_B–

Offset current: I_off

Offset voltage: V_off

[741 op-amp

- 10⁵ open-loop gain

[Differential amplifier

- Simple EKG circuit: uses differential amplifier to cancel common mode signal and amplify differential mode signal

- Realistic EKG circuit: uses two non-inverting amplifiers to first amplify voltage from each load, followed by differential amplifier

- This forms an "instrumentation amplifier"

[Integrator

[Differentiator

[Low-pass filter

- Low-pass filter: simple audio, remove frequencies over 20kHz

Decouple the low-pass RC filter from the load.

- Low-pass filter

[High-pass filter

[Band-pass filter

- Cascading of HPF and LPF

[Comparator: low-voltage alarms, night light controller

[Pulse width modulator: motor controllers

III. Op-amp applications

1) Strain gage

2) Charge amplifier for piezoelectric transducer

- Used to measure force, pressure, acceleration

- Piezoelectric crystal generates an electric charge in response to deformation

3) PID controller

- Output process uses V_ERROR from the PID controller to adjust Vout such that it is ~V_SET

4) PI control

- Temperature control

- Voltage error circuit + proportional integral control circuit

[Books]

Kitchin, A designer's guide to instrumentation amplifiers, 3rd ed.