Electronics and Signal Processing
Electronics and Signal Processing tests device behavior, amplifier circuits, op-amp configurations, filters, sampling, and frequency-domain reasoning. Expect diode and transistor operating regions, bias, small-signal gain, RC filters, Nyquist, and ADC resolution.
Core rules
- Diode: forward biased above threshold, reverse biased as open, breakdown as clamp/regulator with current limiting.
- BJT active region: base-emitter forward, base-collector reverse; IC≈βIB.
- Ideal op-amp with negative feedback: input voltages equal, input currents zero.
- First-order RC low-pass cutoff f_c=1/(2πRC); gain falls 20 dB/decade above it.
- Sampling must exceed twice the highest signal frequency; otherwise aliasing folds energy.
Worked example
An ideal non-inverting op-amp has R1=10 kΩ to ground and Rf=90 kΩ feedback. Gain=1+Rf/R1=10. Input 0.2 V gives 2.0 V output, provided the op-amp output can swing there. For an RC low-pass with R=1 kΩ and C=100 nF, f_c=1/(2π×10³×100×10⁻⁹)≈1.59 kHz.
Traps
Do not apply the virtual-short rule without negative feedback. Ignoring op-amp supply rails produces impossible output voltages. In transistors, assume active mode only after checking VCE. For filters, −3 dB is a power half, not a voltage half. ADC resolution is not accuracy; missing codes, noise, and reference error matter. Anti-alias filtering must precede sampling.