This directory contains a mixed mode pll, combining
ngspice and XSPICE circuit blocks.
The pll consists of the following blocks:
voltage controlled oscillator: vco_sub.cir
digital divider and frequency reference: pll-xspice.cir
phase frequency detector: f-p-det-d-sub.cir
loop filter: loop-filter.cir
main simulation control: pll-xspice.cir

Two test files are included:
test-vco.cir simulates vco frequency versus control voltage
test-f-p-det.cir simulates the phase frequency detector and the loop filter.

The main building blocks are organised as subcircuits.

main simulation control with three reference frequencies:
pll-xspice-fstep.cir