Radiation detection device with improved illumination range having a photodetector that operates in two detecting modes
View Patent ↗A pixel comprises a photodetector and a control circuit. The pixel is provided with an output terminal designed to connect an analysis circuit. The photodetector is configured to have two different operating modes associated with different biasing conditions. A switch connecting the photodetector to the output terminal of the pixel and a circuit for a connecting/disconnecting the control circuit with the output terminal of the pixel and with the photodetector allow to switch between the two operating modes. A comparator compares the voltage across the capacitive load with respect to a threshold value and outputs first and second signals according to the comparison. The comparator is connected to the circuit for connecting/disconnecting the control circuit and to the switch.
1. Device for detecting electromagnetic radiation comprising:
a photodetector provided with two terminals;
a control circuit configured to convert the current issued by the photodetector into a first electrical variable by means of a load;
a pixel including the photodetector and the control circuit, the pixel being provided with an output terminal designed to be connected to an analysis circuit;
a biasing circuit of the photodetector configured to apply a first potential difference across the terminals of the photodetector in a first detecting mode and configured so that one of the terminals of the photodetector is at a floating potential in a second detecting mode, the second detecting mode being a photovoltaic detecting mode whereby the photodetector generates a voltage signal which has a logarithmic relationship to radiation flux received:
a connecting circuit configured to connect the control circuit with the output terminal of the pixel and with the photodetector when the photodetector is in the first detecting mode, and configured to disconnect the control circuit from the output terminal of the pixel and the photodetector when the photodetector is in the second detecting mode;
a switch connecting the photodetector to the output terminal of the pixel and configured to be in the blocking state when the photodetector is in the first detecting mode and to be in the passing state when the photodetector is in the second detecting mode; and
a comparator configured to compare the voltage across the load with respect to a threshold value and configured to deliver a first signal or a second signal according to the comparison, the comparator being connected to the connecting circuit and to the switch.
2. Device according to claim 1 , wherein the comparator is configured so that the control circuit is connected to the photodetector and to the output terminal of the pixel as long as the voltage across the terminals of the load has not reached the threshold value, and so that the photodetector is connected to the output terminal of the pixel when the voltage across the terminals of the load reaches the threshold value.
3. Device according to claim 2 , wherein the connecting circuit comprises a first switch connected between the photodetector and the control circuit.
4. Device according to claim 3 , wherein in that the connecting circuit comprises a second switch connected between the control circuit and the output terminal of the pixel.
5. Device according to claim 4 , wherein the load is a capacitive load comprising an integrating capacitor having a first terminal connected to a circuit configured to apply a fixed potential on the first terminal and in that the comparator is connected to a second terminal of the integrating capacitor.
6. Device according to claim 1 , wherein the connecting circuit comprises a first switch connected between the photodetector and the control circuit.
7. Device according to claim 6 , wherein in that the connecting circuit comprises a second switch connected between the control circuit and the output terminal of the pixel.
8. Device according to claim 7 , wherein the load is a capacitive load comprising an integrating capacitor having a first terminal connected to a circuit configured to apply a fixed potential on the first terminal and in that the comparator is connected to a second terminal of the integrating capacitor.
9. Device according to claim 1 , wherein in that the control circuit is a direct injection circuit with a biasing transistor having a first terminal connected to the photodetector and a second terminal connected to the load, the biasing transistor forms a part of the connecting circuit, a gate electrode of the biasing transistor being connected to the comparator.
10. Device according to claim 9 , wherein the load is a capacitive load comprising an integrating capacitor having a first terminal connected to a circuit configured to apply a fixed potential on the first terminal and in that the comparator is connected to a second terminal of the integrating capacitor.
11. Device according to claim 1 , wherein in that the connecting circuit comprises a second switch connected between the control circuit and the output terminal of the pixel.
12. Device according to claim 1 , wherein the load is a capacitive load comprising an integrating capacitor having a first terminal connected to a circuit configured to apply a fixed potential on the first terminal and in that the comparator is connected to a second terminal of the integrating capacitor.
13. Device according to claim 1 , wherein the comparator comprises an output terminal connected to the analysis circuit and configured to inform the analysis circuit of the detecting mode of the photodetector.