Digital Signal Processing Reference
In-Depth Information
(a)
(b)
20
30
V
DD
V
in
V
bg,in
15
20
V=
bg,in
0V:5V:75V
10
V
out
10
5
0
0
0
5
10
15
20
V
SS
V
in
[V]
Fig. 6.1 a
An inverter with a zero-
V
GS
pull-down transistor and a pull-up transistor with a backgate
bias pin
V
bg
,
in
.
b
Bias voltages up to 75V applied to
V
bg
,
in
increase the noise margin of an inverter
significantly (Myny et al. (
2011
))
6.1 Application Field
The application field for organic DC-DC converters is twofold.
In the first place there is the availability of a technique for tuning a transistor's
V
T
in the applied technology through the backgate that significantly increases the
quality of both digital and analog circuits. This technique requires voltages above
V
DD
. A detailed discussion about the technique is given in
6.1.1
.
In the second place a bias voltage below
V
SS
is required for biasing transistors in
the depletion region and making them behave like resistors. This technique to bias
transistors in the depletion region is discussed in Sect.
6.1.2
.
6.1.1 Dual-
V
T
Technology
The applied organic electronics technology provides the use of backgates. They are
physically located on top of the transistors and influence the
V
T
of the underlying tran-
sistor. This so-called backgate steering technique was elaborated on in Sect.
2.4.2.1
A very important advantage of backgate steering is that this influence of a backgate
voltage on the
V
T
of the transistor is very linear. In Myny et al. (
2011
) the backgate
steering technique was used for tuning the
V
T
of the pull-up transistors in digital
gates. As can be seen in Fig.
6.1
b bias voltages above the supply voltage strongly
improve the noise margin of the inverter with an optimum around 20V for a
V
DD
of 20V. This optimum depends on the relative
W
/
L
sizing between pull-up and
:
pull-down transistors, which is 1
1 in this case.
This same technique, called threshold voltage tuning (TVT), enables some free-
dom in the choice of the DC levels of an analog differential amplifier which facilitates
the DC connection of consecutive amplifiers. A drawback of the single-stage differ-
