Readout technique for increasing or maintaining dynamic range in image sensors
View Patent ↗The apparatus and method provide a readout technique and circuit for increasing or maintaining dynamic range of an image sensor. The readout technique and circuit process each pixel individually based on the magnitude of the readout signal. The circuit includes a gain amplifier amplifying the readout analog signal, a level detection circuit for determining the signal's magnitude, a second gain amplifier applying a gain based on the signal magnitude and an analog-to-digital converter digitizing the signal and a circuit for multiplying or dividing the signal. The method and circuit allow for a lower signal-to-noise ratio while increasing the dynamic range of the imager.
1. A pixel readout circuit for an imager comprising:
a gain circuit comprising:
a first gain amplifier for amplifying a signal from a pixel array;
a signal level determining circuit for determining a gain factor based on a level of the amplified signal; and
a second variable gain amplifier, connected to said signal level determining circuit, for amplifying the signal from the first gain amplifier using the determined gain factor; and
an analog-to-digital converter for digitizing an output of the gain circuit.
2. The readout circuit according to claim 1 , further comprising a circuit for multiplying or dividing an output of said analog-to-digital converter.
3. The readout circuit according to claim 1 , wherein said signal level determining circuit further comprises:
a level detection circuit for determining the signal magnitude of the signal outputted from the first gain amplifier; and
a gain decision circuit for determining the gain to be applied in the variable gain amplifier based on the determined magnitude of the signal.
4. The readout circuit according to claim 1 , wherein said first gain amplifier amplifies the signal to the maximum gain possible.
5. The readout circuit according to claim 2 , wherein said signal, output from said analog-to-digital converter, is multiplied or divided based on the determined signal magnitude.
6. The readout circuit according to claim 1 , wherein an offset is subtracted from the signal before the signal is processed by the first gain amplifier.
7. The readout circuit according to claim 6 , wherein said offset is tunable.
8. The readout circuit according to claim 1 , wherein an offset is subtracted from the signal after the signal is processed by the first gain amplifier.
9. The readout circuit according to claim 8 , wherein said offset is tunable.
10. The readout circuit according to claim 1 , wherein said pixel signal is single ended.
11. The readout circuit according to claim 1 , wherein said pixel signal is differential.
12. An imager comprising:
an array of pixels;
a gain circuit comprising:
a first gain amplifier amplifying a signal from said pixel array;
a signal level determining circuit for determining a gain factor based on a level of the amplified signal;
a variable gain amplifier, connected to said signal level determining circuit, for amplifying the signal from the first gain amplifier using the determined gain factor;
an analog-to-digital converter for digitizing an output of the gain circuit; and
a circuit for multiplying or dividing the signal from said analog-to-digital converter.
13. The imager according to claim 12 , wherein an offset is subtracted from the signal before the signal is processed by the first gain amplifier.
14. The imager according to claim 13 , wherein said offset is equal tunable.
15. The imager according to claim 12 , wherein an offset is subtracted from the signal after the signal is processed by the first gain amplifier.
16. The imager according to claim 15 , wherein said offset is tunable.
17. A method of fabricating a pixel readout circuit comprising the acts of:
fabricating a gain circuit comprising:
fabricating a first gain amplifier for amplifying a signal from a pixel array;
fabricating a signal level determining circuit for determining a gain factor based on a level of the amplified signal; and
fabricating a variable gain amplifier, connected to said signal level determining circuit, for amplifying the signal from the first gain amplifier using the determined gain factor; and
fabricating an analog-to-digital converter for digitizing an output of the gain circuit.