Digital Signal Processing Reference
In-Depth Information
i
(
t
)
i
(
t
)
v
(
t
)
0
i
(
t
)
0
v
(
t
)
v
(
t
)
Figure 1.11
(a) Diode; (b) ideal diode
(a)
(b)
characteristic.
unimpeded in the direction of the arrowhead in its symbol and blocks current flow
in the opposite direction. Hence, the ideal diode is a short circuit for current flow in
the direction of the arrowhead [when tends to be positive] and an open circuit
for current flow in the opposite direction [when is negative]. The diode is a non-
linear device; therefore, many circuits that contain diodes are nonlinear circuits.
One circuit for a power supply is given in Figure 1.12(a). The power-supply
load is represented by the resistance and the voltage across this load is the half-
wave rectified signal of Figure 1.12(b). The load current is the load voltage
divided by is also shown in Figure 1.12(b). We see then that the volt-
age across the load is unidirectional; however, this voltage is not constant.
A practical dc power supply is illustrated in Figure 1.13. The inductor-capacitor
(
LC
) circuit forms a low-pass filter and is added to the circuit to filter out the
voltage variations so that the load voltage is approximately constant.
A circuit that uses four diodes to generate a full-wave rectified signal is given in
Figure 1.14. The diodes A and D conduct when the source voltage is positive, and the
diodes B and C conduct when the source voltage is negative. However, the current
v(t)
v(t)
R
L
,
i
L
(t)
v
L
(t)
R
L
; i
L
(t)
v
L
(t)
Diode
i
L
(
t
)
ac
voltage
source
v
L
(
t
)
R
L
Load
(a)
v
L
(
t
)
i
L
(
t
)
T
0
0
T
0
/2
T
0
2
T
0
t
(b)
Figure 1.12
Half-wave rectifier.
