Amplifier Design - Analog Organic Electronics - page 92

Table 3.4 Summary of the
measurement results for the
comparator integrated on
plastic foil (Marien et al.
2009 )

S pecification V alue

Power supply 20V

Gain 12dB

Band width 1kHz

Current consumption 9 µ A

Power 180 µ W

2 × 3mm 2 Chip area

3.4 Conclusion

The first step in the exploration of analog circuits design in organic electronics was
the design of an amplifier. This amplifier must be adapted to the limits and the
challenges but also to the advantages and the available tricks in the technology.
In the case of organic electronics technology on foil this means that only p-type
transistors are available and that special care is required for variations of behavioral
transistor parameters such as V T whereas the backgate of the transistors can be
advantageously employed to increase the circuit performance. From the knowledge
about the technology provided inChap. 2 a carefully considered design of an amplifier
can be made.
In this chapter first the application field of organic amplifiers was highlighted.
They are required for more complex analog and mixed-signal circuits such as ADCs
and sensor interfaces. As an amplifier should be usable in a variety of applications
no direct specifications were deducted: the gain and the bandwidth should generally
be as high as possible.
Consequently the best amplifier topology was searched for. A differential ampli-
fier was preferred over a single-ended amplifier on the basis of the threshold voltage
suppression ratio. Furthermore the bootstrapped gain-enhancement load was pre-
sented as the best p-type transistor solution -better than a zero- V GS load, a diode
load or a hybrid load- to replace the unavailable n-type load transistors.
Then several amplifier designs were presented and their measurement results were
discussed:
First, a single-stage amplifier was presented with a gain of 15dB. This single-
stage amplifier was consequently employed together with high-pass level shifters in
a 3-stage op amp.
Then an improved amplifier was presented that has identical DC operating points
for the input and output voltages and that can as a result easily be employed in
more-stage amplifiers. This was demonstrated with a 2-stage op amp that has a gain
of 20dB. This op amp was the first DC-coupled more-stage amplifier reported in
literature.
Finally a classic comparator was constructed from a basic differential amplifier.
The single-stage comparator had a gain of 12dB and performed at a clock speed of
1kHz.