Analog and Digital Electronics
Analog and Digital Electronics tests semiconductor devices, amplifiers, op-amps, logic gates and microprocessors. Expect bias calculations, amplifier gain, Boolean simplification and basic microprocessor architecture.
Analog electronics
- A diode conducts when forward biased above its cut-in voltage; a Zener diode regulates in reverse breakdown.
- BJT regions: cutoff, active and saturation; β = IC/IB.
- Op-amp ideal rules with negative feedback: input current is zero and the differential input voltage is zero (virtual short).
- Inverting amplifier gain = −Rf/Rin; non-inverting gain = 1 + Rf/Rin.
Digital electronics and microprocessors
- Logic gates implement Boolean operations; NAND and NOR are universal gates.
- De Morgan’s laws: (A·B)′ = A′ + B′ and (A + B)′ = A′·B′.
- A microprocessor such as the 8085 has an ALU, registers, control unit and buses; instructions move data, perform arithmetic/logic and control flow.
Worked example
An inverting op-amp has Rin = 10 kΩ, Rf = 100 kΩ and Vin = 0.2 V. Gain = −Rf/Rin = −100/10 = −10. Therefore Vout = −10 × 0.2 = −2 V. The negative sign shows phase inversion.
Traps that cost marks
Applying the virtual-short rule without negative feedback, mixing inverting and non-inverting gain formulas, and assuming a BJT in saturation has the same β as in the active region are common errors. In digital circuits, remember that unused CMOS inputs must not float.