Electronic Circuits and Applications
Electronic Circuits and Applications
This domain tests amplifier configurations, oscillator conditions, rectifier and filter behaviour, and the logic gates and sequential blocks of basic digital electronics.
Core rules
- Gain in decibels: dB = 20 log (Vout/Vin) for voltage, 10 log (Pout/Pin) for power; a gain of 10 is 20 dB, a gain of 0.5 is −6 dB.
- Op-amp inverting amplifier: Av = −Rf/Rin (180° inversion). Non-inverting: Av = 1 + Rf/R1, input in phase.
- Barkhausen criterion: loop gain Aβ = 1 with total phase shift of 0° or 360° at the oscillation frequency. An RC phase-shift oscillator uses three 60° sections; a Wien bridge needs Rs/R = 2 for the amplitude condition.
- Rectifiers: half-wave ripple factor 1.21, efficiency about 40 %; full-wave/bridge 0.482 and about 81 %. A shunt capacitor raises DC output and lowers ripple.
- Logic gates: AND is the product, OR the sum; NAND and NOR are universal. De Morgan: (A·B)' = A' + B' and (A + B)' = A'·B'.
- Sequential blocks (flip-flops, counters, registers) hold state; combinational blocks (adders, multiplexers, decoders) do not.
Worked example
An inverting amplifier has Rin = 10 kΩ, Rf = 100 kΩ and a 50 mV input. Voltage gain = −100k/10k = −10, so the output is 500 mV, inverted in phase. In decibels: 20 log 10 = 20 dB; the minus sign is phase inversion, not attenuation, so the magnitude is still 20 dB of gain. With ±12 V supplies, a 0.5 V output is far below clipping, so the small-signal model is valid.
Mark-losing traps
- Reporting the inverting gain as positive, or reading the minus sign as a dB loss.
- Using 20 log for power ratios.
- Applying Barkhausen with loop gain above or below exactly unity.
- Forgetting that NAND alone can build every other gate.