Annual report 2000 - Europractice

A CMOS readout circuit for thin film pyroelectric array detectors
Application
Thin film pyroelectric array detectors
are a new range of products
designated to the detection of infrared
light of wavelengths up to 20
µm. Their very low intrinsic noise
allows for uncooled operation of
these detectors, thus opening the
way to low-cost analytical infrared
spectrometers. Nevertheless, due to
their small dimensions, thin film
pyroelectrics deliver ac signals of a
few picoamperes with output impedances
in the order of 50 GΩ
and require highly sensitive interface
circuits. This, together with the
required parallel readout of up to
128 pixels, make the use of an ASIC
for this type of array detector
mandatory.
The array detector was developed
by the Ceramics Laboratory (LC) of
the Swiss Institute of Technology in
Lausanne (EPFL). The detector unit
is now commercialised by IR Microsystems
SA in Lausanne.
Design
The ASIC is a 16-channel readout
circuit implemented in a 0.7 µm
CMOS technology where each
channel consists of a high gain transimpedance
preamplifier, followed
by a multiplier for signal demodulation,
an integrator over 8 periods, a
12-bit A/D converter and a data
buffer. Design criteria for the ASIC
were a minimum gain of the preamplifier
of 10 GΩ at an operation
frequency of 10 Hz with a linearity
up to input signals of 10 pA, an
input-referred current noise inferior
to the detector noise (which is
2.25 fA/Hz 1/2 at 10 Hz) and a preamplifier
input leakage current inferior
to the signal amplitude up to
70°C.
A main measure to a reduction of
the preamplifier noise reduction is
the implementation of input transistors
with dimensions of
5x5000 µm 2 .
Prototyping
The ASIC was integrated in two
steps: a first prototype including the
analog part up to the integrator was
fabricated by IMEC through the
EUROPRACTICE MPW service in
to verify the performance of the
preamplifier. After successful tests,
the complete chip was fabricated
through a second EUROPRAC-
TICE MPW run and tested at EPFL
LC and LEG.
Small Volume Fabrication
The EPFL start-up company IR Mi-
The pyroelectric array detector
(1x64 pixels)
The ASIC in Alcatel Microelectronics
0.7µ CMOS technology.
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service
center
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IMEC
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crosystems SA has started production
via EUROPRACTICE with a
first batch of 1300 chips. The chips
are packaged in a PQFP100 and
tested by EUROPRACTICE. This
batch is designated for the prototyping
and qualification of the IR Microsystems
detector units as well as
the first commercial units.
Why Europractice?
Good technical support
MPW service
Flexible offer for low volume production
Specifications
Technology: Alcatel Microelectronics
0.7µ C0.7M-A
Die size: approx. 6900x4000 µm 2
Mixed signal approx. 50 % / 50 %
Max input: 10 pA
Resolution:12 bit
Output noise: 0.64 LSBRSM
For further information,
please contact
IR Microsystems SA
PSE – Bât. A, CH-1015
Lausanne
info@ir-microsystems.com
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