Active Devices › Oscillators
VCO & Oscillator Designer
Complete VCO and oscillator design tool — Leeson equation phase noise estimator, LC tank circuit component values, Colpitts/Hartley topology design, tuning sensitivity, VCO gain KV, pulling figure and pushing figure.
// Oscillator Specifications
MHz
dB
dBm
kHz
// LC Tank Circuit Design
nH
pF
× (Cmax/Cmin)
V
Resonance: f0 = 1/(2π√LC)
Colpitts: C1∥C2 in shunt, L in series. Feedback ratio n = C1/(C1+C2)
Start-up condition: gm ≥ (C1+C2)² / (C1·C2·Rp)
where Rp = Qu·ω0·L (parallel tank resistance)
Colpitts: C1∥C2 in shunt, L in series. Feedback ratio n = C1/(C1+C2)
Start-up condition: gm ≥ (C1+C2)² / (C1·C2·Rp)
where Rp = Qu·ω0·L (parallel tank resistance)
// Leeson Phase Noise Results
Leeson Equation
Phase noise L(f) at 100 kHz offset—
Phase noise L(f) at 1 MHz offset—
Phase noise L(f) at 10 MHz offset—
Noise floor (far from carrier)—
1/f³ corner (flicker region)—
Tank Circuit
Required capacitance C—
Tank parallel resistance Rp—
Coupling capacitor Ccoup—
Oscillation start-up gm,min—
VCO Performance
Tuning sensitivity KV—
Tuning range Δf—
VCO figure of merit (FOM)—
Pushing figure (est.)—
Pulling figure (est.)—
// Phase Noise vs Offset Frequency
Leeson model — 1/f³ region (flicker), 1/f² region (thermal), noise floor
// Typical Phase Noise Reference
| Oscillator Type | QL | @ 100 kHz | @ 1 MHz | Application |
|---|---|---|---|---|
| LC VCO (CMOS) | 10–30 | −90 dBc/Hz | −115 dBc/Hz | PLL reference |
| LC VCO (bipolar) | 20–50 | −110 dBc/Hz | −130 dBc/Hz | Mobile PA LO |
| Dielectric resonator | 1000–10000 | −130 dBc/Hz | −155 dBc/Hz | Base station LO |
| Crystal oscillator | 50k–500k | −150 dBc/Hz | −170 dBc/Hz | Reference, TCXO |
| SAW oscillator | 5000–20000 | −120 dBc/Hz | −145 dBc/Hz | Narrowband TX |
Leeson equation:
L(f) = 10·log[F·kT/(2Ps) × (1+(f0/2QLf)²) × (1+fc/f)]
F = amplifier noise factor (linear) · k = 1.38×10⁻²³
Ps = signal power at resonator · fc = 1/f corner frequency
L(f) = 10·log[F·kT/(2Ps) × (1+(f0/2QLf)²) × (1+fc/f)]
F = amplifier noise factor (linear) · k = 1.38×10⁻²³
Ps = signal power at resonator · fc = 1/f corner frequency