Three Phase Generator

The circuit

An oscillator consists of two sections, an active element and a feedback network. Together they form a closed loop. When disconnecting this loop and injecting a test signal, both the input and output signals around the loop are uniform in phase and magnitude at the resonant frequency. If the loop gain drops below unity, then oscillation of the closed loop would decay exponentially. If the gain exceeds unity, then the loop gain would be limited to unity due to clipping nonlinearities. This effect can be observed with the following example. Three cascaded RC circuits and inverters form a closed loop system. Conditions for oscillation are satisfied when the phase lag of the RC circuits equals 60 degrees. At nodes (2), (4) and (6), three phase-lagged sine waves are produced and may be used as control signals for three phase power inverters.

The input file (three_phase_generator.cir)

three phase generator

* fo = 1 / (2 pi r c 3^(1/2))

.control
tran 0.05ms 10ms uic
plot v(2) v(4) v(6) xlabel t[s] ylabel output[V] title 'TRAN analysis'
.endc

x1 1 2 invertor
x2 3 4 invertor
x3 5 6 invertor

r1 6 1 100k
r2 2 3 100k
r3 4 5 100k

c1 1 0 10n ic=0
c2 3 0 10n ic=7.5V
c3 5 0 10n ic=15V

.subckt invertor 1 2
v0 4 0 dc 15V

r1 1 3 100k
r2 2 3 820k

m1 2 3 4 4 pmos
m2 2 3 0 0 nmos
.ends

.model pmos pmos
.model nmos nmos

.end

The results