Analog and Digital Circuit Design
Core concepts
Candidates should understand operational amplifier configurations (inverting, non-inverting, buffer, summing, integrator, comparator), gain formulas, and the ideal op-amp assumptions of infinite gain and input impedance with zero output impedance. Know filter types-RC low-pass and high-pass with cutoff f = 1/(2πRC)-and the meaning of decibels (20 log for voltage, 10 log for power). Digital topics include Boolean algebra, truth tables, Karnaugh maps, combinational logic (adders, multiplexers, decoders), and sequential logic (flip-flops, registers, counters). Understand setup and hold timing, propagation delay, and the difference between synchronous and asynchronous design.
Traps
A frequent error is applying the inverting gain formula (−R_f/R_in) to a non-inverting circuit, whose gain is 1 + R_f/R_in. Questions may present a logic expression needing simplification; check with a truth table rather than guessing. Watch active-low signals and De Morgan's theorem. In timing questions, remember setup time is before the clock edge and hold time is after it. Another trap: assuming an op-amp output can exceed its supply rails-it cannot.
Worked example
An inverting amplifier has R_in = 2 kΩ and R_f = 20 kΩ, input 0.2 V. Gain is −10, so output is −2.0 V, valid only if supplies exceed 2 V. Rule of thumb: always verify the output stays within the supply rails before declaring a design correct.