PLL Phase Noise Budget

Integer-N model: f_pfd = f_ref/R, N = f_out/f_pfd. PFD/CP in-band floor = FOM + 20log₁₀N + 10log₁₀f_pfd; flicker = FOM_fl + 20log₁₀(f_out/1 GHz) − 10log₁₀(offset) (standard ADI/TI model). Reference noise reaches the output ×20log₁₀(N/R).

Loop: type-2 2nd-order open loop G(s) = K(1+s/ω_z)/(s²(1+s/ω_p)) with ω_z = ω_c/k, ω_p = kω_c, k = tan(45°+pm/2), |G(jω_c)| = 1. Reference + PFD noise see the lowpass |G/(1+G)|; VCO sees the highpass |1/(1+G)|. Peaking grows as phase margin drops (≈2.6 dB at 50°, ≈6 dB at 30°).

dBc/Hz at f_ref. Log-log linear interpolation between points, flat beyond the ends.

Free-running VCO at f_out, dBc/Hz.