APPLICATION NOTE
3
Controlled Reactance VCO
A more circuit oriented approach to build a VCO is to take a simple tank oscillator and use a voltage-dependent
reactance for one of the tank components. The following example is a Colpitts oscillator. The zx device is used to
implement a voltage-controlled lossy inductor.
xvi ctrl 0 ref vcc c zx;Colpitts with variable tank element,
lref ref ref1 15u
rref ref1 0 2.0
c1 c e 20n
c2 e 0 200n
q1 c 0 e q2n2222
re e vee 2k
vcc vcc 0 10v
vee vee 0 -10v
vctrl ctrl 0 pwl(0,1.5v 124u,1.5v 125u,2.5v)
.ic v(c) = 10 v(e) = -0.7
Figure 4: Circuit Design for Controlled Reactance VCO
