16
S. Kar
Fig. 11 Equivalent circuit of IMPATT diode with RF circuit and load
The condition for stable oscillation is obtained by equating the real parts of Y D
and Y C in Eq. 21a, 21b, when we have:
g L = −G D − B
2
D R s
(22)
But when the imaginary parts of Y D and Y C are equated, we obtain the frequency
of oscillation as:
f 0 =
1
2π
√
L c C d
(23)
The power output of the oscillator is given by:
P out =
1
2
g L V
2
r. f
(24)
At oscillation threshold when v r.f = 0, Eqs. (19a and 19b) simplifies to:
G D | S D R = −3
α
θ 2 (1 − cos θ)I th
(25a)
G D | D D R = −
3
2
α
θ 2 (1 − cos θ)I th
(25b)
In the practical situation, since B
2
D R s is fixed and the magnitude of G D increases
with current, it is a good approximation to take g L = 0 at oscillation threshold. Because
oscillation can only occur when the negative conductance exceeds the magnitude of
B
2 R s , the oscillation threshold may be obtained from:
−G D0 = B
2
D R s
(26)
S. Kar
Fig. 11 Equivalent circuit of IMPATT diode with RF circuit and load
The condition for stable oscillation is obtained by equating the real parts of Y D
and Y C in Eq. 21a, 21b, when we have:
g L = −G D − B
2
D R s
(22)
But when the imaginary parts of Y D and Y C are equated, we obtain the frequency
of oscillation as:
f 0 =
1
2π
√
L c C d
(23)
The power output of the oscillator is given by:
P out =
1
2
g L V
2
r. f
(24)
At oscillation threshold when v r.f = 0, Eqs. (19a and 19b) simplifies to:
G D | S D R = −3
α
θ 2 (1 − cos θ)I th
(25a)
G D | D D R = −
3
2
α
θ 2 (1 − cos θ)I th
(25b)
In the practical situation, since B
2
D R s is fixed and the magnitude of G D increases
with current, it is a good approximation to take g L = 0 at oscillation threshold. Because
oscillation can only occur when the negative conductance exceeds the magnitude of
B
2 R s , the oscillation threshold may be obtained from:
−G D0 = B
2
D R s
(26)