Digital Signal Processing Reference
In-Depth Information
(a)
80
(b)
1
60
0.8
50
60
0.6
40
40
0.4
30
20
0.2
20
I
out,ext
=0
μ
A
I
out,ext
=10
μ
A
P
out,ext
@10
μ
A
η
c
@10
μ
A
0
0
10
15
20
25
15
20
25
V
DD
[V]
V
DD
[V]
Fig. 6.13 a
Measured DC output voltage of the 3-stage Dickson converter as a function of supply
voltage
V
DD
. The black line is the output voltage for a purely capacitive load, the gray line the
output voltagewith a 10
A load current. For thismeasurement
V
in
is connected to
V
DD
.
b
Measured
output power (
solid line
) and core power efficiency (
dashed line
) of the converter for varying supply
voltage. For this measurement
V
in
is connected to
V
DD
µ
between two transistors biased in the same region is already limited, it even decreases
further when they are biased in a different region, i.e. saturation versus cut-off.
A measure that partly explains the quality of this converter is its core efficiency,
i.e. the ratio between the current at the output flowing through the load,
I
out
,
ext
, and
the current at the output flowing back in the converter due to the non-ideal diodes,
I
out
,
int
.
I
out
,
ext
I
out
,
ext
+
η
c
=
(6.7)
I
out
,
int
V
out
|
I
out
=
10
μ
A
−
V
out
|
I
out
=
0
μ
A
V
out
|
I
out
=
10
μ
A
−
η
c
=
(6.8)
V
out
,
ideal
The core efficiency, calculated from equation (
6.7
), is a measure of the behavior of
the converter with a specific load current. In Fig.
6.13
b the output power and the core
efficiency of the Dickson converter are deduced from the measured behavior in the
case of a 10
W is obtained for
the 25V supply voltage. The dashed curve visualizes the converter core efficiency,
calculated from equation (
6.8
).
A maximal core efficiency of 48% is reached in this converter. The best metric
of a converter is its overall efficiency
µ
A load current. An output power of up to 65010
µ
, which is calculated from equation (
6.9
) and
where the power of the clock generation circuit is included in the calculation. This
efficiency is only around 4% which is mainly caused by the clock driving circuit
that consumes static power. This phenomenon is further discussed in Sect.
6.4
.
η
P
out
,
ext
|
I
out
=
10
μ
A
P
tot
η
=
(6.9)
