A sawtooth differs from a triangle in one crucial way: asymmetric slopes. The ramp rises slowly and resets nearly instantaneously (or vice versa). This makes it the workhorse for CRT/oscilloscope timebases, PWM carrier generation in switching regulators, and the fundamental waveform in subtractive synthesizers — its harmonic content (every integer harmonic, rolling off at 6 dB/octave) is sonically rich and easy to filter.

The classic topology is a constant-current charged capacitor with a fast discharge switch. A current source I charges capacitor C linearly: V(t) = (I/C)·t. When the voltage hits a threshold, a comparator fires a transistor (BJT, JFET, or MOSFET) across C, dumping the charge in microseconds. Release, and the ramp starts again.

Concrete example — 1 kHz sawtooth for a synth VCO:

• Target peak: 5 V, period: 1 ms (so ramp time ≈ 1 ms, ignoring tiny reset).
• Pick C = 10 nF (small enough to discharge fast, large enough to swamp stray capacitance).
• Required current: I = C·ΔV/Δt = (10 nF × 5 V) / 1 ms = 50 µA.
• Build the current source from a PNP with emitter resistor: I ≈ (V_CC − V_BE − V_ref) / R_E. With V_CC = 12 V and a 5 V reference on the base, R_E ≈ (12 − 0.7 − 5)/50 µA ≈ 126 kΩ.
• Comparator (LM311) compares the ramp to 5 V; output drives a 2N3904 saturated across C. Add a small base resistor (1 kΩ) and keep the collector trace short — the discharge current spike can reach tens of milliamps for a few hundred nanoseconds.

Linearity rule of thumb: for <1% nonlinearity, the current source's output impedance must be at least 100× the load it drives. A bare resistor "current source" (just R to V_CC) gives terrible linearity because as V_C rises, charging current droops — the ramp curves into an exponential. A proper current mirror or JFET source fixes this.

Reset glitch is the dominant practical issue. During discharge, the comparator sees the threshold for a finite time, the transistor has finite turn-off delay, and the cap recharges slightly before the transistor fully opens. The result: amplitude jitter and frequency drift with temperature. Synth designers add a one-shot (74HC123) to enforce a fixed, short reset pulse rather than relying on comparator hysteresis alone.

For voltage-controlled sweep (oscilloscope timebases, VCOs), replace the fixed current source with a transconductance stage (OTA like LM13700, or a voltage-to-current converter). Frequency now tracks input voltage linearly — exactly what an exponential converter feeds for 1V/octave synth tuning.