🔄Oscillators

An oscillator converts DC power into a periodic AC signal without any external input — it is a self-sustaining system. All oscillators need: amplification (gain to overcome losses), positive feedback (signal fed back in phase), and a frequency-determining element (RC, LC, or crystal). The Barkhausen criterion: loop gain ≥ 1, loop phase shift = 0° or 360°.

Wien Bridge: uses RC network + op-amp. Produces low-distortion sine waves for audio (20Hz-20kHz). f = 1/(2πRC). Requires automatic gain control (incandescent bulb or JFET). Phase Shift: three RC stages, each shifts 60°. Total: 180° + 180° from amplifier = 360°. Simple but sensitive to component variations.

Colpitts: capacitive divider feedback (C1, C2 across inductor). f = 1/(2π√(LC_eq)), where C_eq = C1·C2/(C1+C2). Popular in RF because capacitors are more stable than inductors. Hartley: inductive divider. Clapp: improved Colpitts with extra capacitor in series with inductor for better stability. Used in radio transmitters, receivers, and RF test equipment (10kHz-1GHz+).

The most popular IC ever made (1972, Hans Camenzind/Signetics). Over 1 billion sold annually. Astable mode (oscillator): frequency f = 1.44/((R1+2R2)C), duty cycle = (R1+R2)/(R1+2R2). Monostable mode (one-shot): pulse width = 1.1×R×C. Supply: 4.5-16V, output: up to 200mA. Used in LED flashers, PWM generators, tone generators, timers.