Integrated Circuits
Description and operation of logic and linear circuits; introduction to operational amplifiers used as integrator, differentiator, voltage follower, comparator and summing amplifier.
Integrated circuits, summary notes
- Integrated circuits are either digital (logic) or analogue (linear). The operational amplifier is the classic linear IC.
- An ideal op-amp has infinite open-loop gain, infinite input impedance and zero output impedance.
- Common configurations: inverting amplifier, non-inverting amplifier, voltage follower (buffer, gain = 1), comparator, integrator, differentiator and summing amplifier.
- Negative feedback returns part of the output out of phase with the input. It reduces gain but improves stability, bandwidth and linearity.
- Positive feedback reinforces the input and causes oscillation, the basis of oscillator circuits.
- ⚠ Exam trap: negative feedback trades gain for stability and bandwidth. A voltage follower has a gain of exactly 1, not the infinite open-loop figure.
- Inverting amplifier gain
- A_v = −R_f / R_in
- Non-inverting amplifier gain
- A_v = 1 + (R_f / R_in)
- Voltage follower
- A_v = 1
An inverting op-amp has R_f = 100 kΩ and R_in = 10 kΩ. What is its voltage gain?
A_v = −R_f/R_in = −100/10 = −10. The magnitude is 10 and the minus sign indicates 180° inversion.
What is the purpose of a voltage follower if its gain is only 1?
Impedance matching. Its very high input impedance avoids loading the previous stage, while its low output impedance can drive the next stage, it buffers without altering the signal level.
Operational amplifier explorer
Integrated circuits concept map
Integrated Circuits
Integrated circuits quiz
Integrated Circuits, quiz
1. The operational amplifier circuit shown has a 100 kOhm feedback resistor and a 10 kOhm input resistor. Its voltage gain is:
-10+11-0.12. An inverting operational amplifier has a feedback resistor of 100 kΩ and an input resistor of 10 kΩ. Its voltage gain is:
−10−0.1+113. A non-inverting operational amplifier has a feedback resistor of 100 kΩ and an input resistor of 10 kΩ. Its voltage gain is:
+11+10−104. An op-amp connected as a voltage follower has a voltage gain of:
OneInfiniteMinus one5. An ideal operational amplifier has:
Infinite gain, infinite input impedance, zero output impedanceZero gain and zero input impedanceFinite gain and infinite output impedance6. Negative feedback in an amplifier:
Reduces gain but improves stability and bandwidthIncreases gain and causes oscillationHas no effect on bandwidth7. An inverting op-amp with R_f = 100 kΩ and R_in = 10 kΩ has a gain of:
−10−0.1+118. A non-inverting amplifier has a gain given by:
1 + R_f/R_in−R_f/R_inR_in/R_f9. Integrated circuits are broadly divided into:
Digital and analogue (linear)Active and passiveSeries and parallel10. An op-amp used to compare two input voltages and give a high or low output is a:
ComparatorIntegratorVoltage follower