Integrated Circuits and Op-Amp Basics
7. Integrated Circuits and Op-Amp Basics
This domain tests IC classification and packaging, and the ideal op-amp with its two standard amplifier circuits.
IC basics
- By integration: SSI (up to about 100 components), MSI, LSI, VLSI. By function: linear (741 op-amp, 555 timer, 7805 regulator) and digital (7400 NAND, 7408 AND).
- The 741 is an 8-pin DIP: pin 2 inverting input, pin 3 non-inverting input, pin 4 V−, pin 6 output, pin 7 V+.
Op-amp principles
- An ideal op-amp has infinite open-loop gain, infinite input impedance, zero output impedance and infinite bandwidth; practical devices differ, so negative feedback is used.
- With negative feedback the input terminals sit at almost the same potential - the virtual ground at the inverting input.
- Inverting amplifier: A = −R_f/R_in, input impedance = R_in.
- Non-inverting amplifier: A = 1 + R_f/R_1.
- Voltage follower (R_f = 0, R_1 open) gives A = 1 with high input impedance.
- Comparator: no feedback, so the output saturates at ±V_supply.
- CMRR and slew rate limit real performance; the 555 timer is a separate IC used for astable and monostable timing.
Worked example
An inverting amplifier uses R_in = 1 kΩ and R_f = 10 kΩ, with V_in = 0.5 V. Gain = −10 kΩ/1 kΩ = −10. V_out = −10 × 0.5 V = −5 V, within a ±12 V supply, so no clipping occurs.
Traps
- Using the inverting formula for a non-inverting circuit.
- Dropping the minus sign, or expecting the output to exceed the supply rails.
- Applying the virtual-ground idea to a comparator or an open-loop circuit.
- Confusing supply pins 7 and 4 on the 741.