Thermal measuring and testing – Temperature measurement – By electrical or magnetic heat sensor
Reexamination Certificate
2002-06-05
2004-03-30
Gutierrez, Diego (Department: 2859)
Thermal measuring and testing
Temperature measurement
By electrical or magnetic heat sensor
C374S141000, C250S2140AG
Reexamination Certificate
active
06712506
ABSTRACT:
DESCRIPTION
1. Technical Field
This presentation discloses an invention relating to a reader for an electromagnetic radiation detection element and an image sensor including such a reader. The invention also relates to a read process that could be implemented by this reader.
An image reader means a device capable of transforming an electronic signal supplied by one or several electromagnetic radiation detection elements into a signal that can be used to represent or record an image, or at least an element of an image (pixel).
The invention is used for applications in different types of image sensors, for example such as cameras. These image sensors may be equipped with detection elements in the form of field effect diodes or elements (MOSFET). In particular, the invention may be used for devices equipped with a sensitive retina integrated in thin layers (TFA Thin Film on Asic).
The invention is also used for applications in the instrumentation (spectroscopic, etc.) and robotics (sensors) fields.
2. State of the Art
The state of the art closest to the invention is described in document (1), for which the complete reference is given at the end of the description. It is also illustrated in
FIG. 1
, extracted from document (1) and described below to facilitate understanding of the rest of the presentation.
FIG. 1
shows an electrical diagram of a reader
10
associated with an electromagnetic radiation detection element. The detection element shown in the form of a diode
12
is associated with an impedance matching circuit
14
or an input stage, designed essentially to polarize the diode and collect the charges that are generated in it by radiation. The detection element, in the event diode
12
, is capable of converting electromagnetic radiation, for example visible or infrared light, or y radiation, into a current of electrical charges. The charge current denoted I
ph
in the figure is transmitted through the impedance matching circuit
14
to the reader
10
itself. (The reader
10
is usually also called the preamplifier-integrator).
The reader
10
comprises integration means in the form of a capacitor
16
. The capacitor is charged by the electronic current I
ph
in an integration phase and there is a voltage denoted V
int
at its terminals. The voltage V
int
represents the intensity of the radiation flux received by the detection element during the integration phase.
An amplifier
18
connected to a terminal
20
of the capacitor
16
supplies a detection signal that varies linearly with the voltage V
int
. The amplifier in particular connects the terminal
20
of the capacitor to a read signal bus
22
. The bus
22
is considered as being a constituent of an output stage from the reader or as forming part of such an output stage.
The terminal
20
of the capacitor
16
is also connected to the inverter input of a comparator
24
. The comparator is designed to compare the voltage V
int
with a set voltage V
comp
and to control opening of a switch
27
when the voltage V
int
goes above the set voltage threshold V
comp
. When the switch
26
is open, the reader
10
is isolated from the detection element
12
.
Opening the switch
27
also interrupts integration of the current in the capacitor
16
, and prevents a reader saturation phenomenon when the radiation flux received by the detection element is very intense.
It can be seen that the rate of the comparator
24
is controlled by a “Clock” signal such that opening the switch
26
also has to be validated by a synchronization pulse.
Synchronization pulses are also produced for initialization of the reader before each new integration phase. These pulses then temporarily close a switch
28
connected between the terminals of the capacitor
16
, to discharge it.
According to one interesting feature of the reader, it also comprises a timed indication stage
30
capable of outputting a signal representing the duration of each integration phase. Essentially, this signal is provided by a second capacitor
36
connected to a time signal bus
32
through an amplifier
38
. The capacitor
36
is connected to a charge voltage source V
ramp
through a switch
37
, which is also opened under the control of the comparator
24
.
By combining the sampled voltage blocked by the time indication stage
30
(integration time T
int
) and the voltage integrated in the capacitor
16
(integrated photocharge Q
int
), it is then possible to obtain the value
I
p
h
=
Q
int
T
int
and consequently the incident flux.
A more complete description of the operation of the device in
FIG. 1
is given in document (1) mentioned above, although it is not necessary for a good understanding of the invention.
Image sensors equipped with a device like that described above can significantly increase the speed at which images are taken.
PRESENTATION OF THE INVENTION
The purpose of the invention is to propose a reader operating essentially on the principle of the reader described above, and which has improved operating characteristics.
One purpose in particular is to propose such a reader with low reading noise.
Another purpose is to propose such a reader with improved sensitivity.
There is another purpose related to the previous purpose, which is to propose such a reader that can operate with a low capacity integration capacitor, and that can therefore reduce the surface area of the integration capacitor.
Another purpose of the invention is to propose a read process and a sensor, or detection device, using one or several readers conform with the invention.
In order to achieve these purposes, more precisely the invention relates to a reader for an electromagnetic radiation detection element comprising:
at least one electrical charge integration capacitor that can be connected to at least one electromagnetic radiation detection element, to output a voltage that it is a function of the electrical charges supplied by the said detection element,
an amplifier connected between the capacitor and an output stage from the reader, the amplifier having a high impedance terminal connected to the integration capacitor and a low impedance terminal connected to the output stage, and
comparator means for isolating the integration capacitor from the detection element when the voltage at the capacitor terminals is greater than a set value.
According to the invention, the comparator means are connected to the low impedance terminal of the amplifier.
Since the comparator means are connected to the low impedance terminal of the amplifier, in other words to the terminal connected to the output stage, their input capacitance is not in parallel with the integration capacitor. The result is an increase in the current-voltage conversion factor, creating better sensitivity.
The available voltage at the output from the amplifier reflects the voltage at the capacitor terminals. Therefore, it is used to determine whether or not it exceeds a given value.
Furthermore, the amplifier does not amplify an input noise inherent to the comparator means and to a comparison voltage source applied to these means, if any. This can significantly reduce noise transferred to the output stage.
According to an improvement to the reader, a switch can be connected between the low impedance terminal of the amplifier and the comparator means, to connect the comparator means to the amplifier during an integration phase and to isolate the comparator means from the amplifier during a read phase.
Due to this improvement, the comparator means may be completely isolated from the amplifier and from the output stage to protect the output stage from noise generated by these means.
According to another improvement of the reader, an additional switch may be connected between the amplifier and the output stage, to connect the output stage to the amplifier in a read phase and to isolate the output stage from the amplifier in an integration phase.
This improvement has a number of advantages.
During the integration phase, the low impedance output from the reader is charged solely by t
Commissariat a l'Energie Atomique
Gutierrez Diego
Harness & Dickey & Pierce P.L.C.
Jagan Mirellys
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