Multi-beta pixel circuit and image sensor circuit using same
An image sensor uses a pixel circuit which includes a BJT phototransistor having multiple selectable beta values. The BJT is one semiconductor device includes: a substrate having a first conductivity type; a first well having the first conductivity type; a collector electrode having the first conductivity type in the first well; a second well having a first concentration of a second conductivity type; a first emitter electrode having the first conductivity type in the second well; a base electrode having the second conductivity type in the second well; a third well having a second concentration of the second conductivity type, wherein the second concentration is different from the first concentration; and a second emitter electrode having the first conductivity type in the third well.
1. A pixel circuit for use in an image sensor, comprising:
a bipolar junction transistor (BJT) having a base, a collector, and a plurality of emitters, wherein the BJT is a phototransistor whose current generates a pixel signal for the pixel circuit;
a shutter control stage configured to operably control an exposure of the BJT;
a readout stage configured to operably read out the pixel signal; and
one or more switches configured to respectively control corresponding one or more of the plurality of emitters;
whereby the BJT has multiple selectable beta values by controlling the one or more switches.
2. The pixel circuit of claim 1 , further including a storage device for storing the pixel signal.
3. The pixel circuit of claim 1 , wherein a total number of the switches corresponds to a total number of the emitters.
4. The pixel circuit of claim 1 , wherein a total number of the switches corresponds to a total number of the emitters minus one.
5. The pixel circuit of claim 1 , wherein the BJT is one semiconductor device including:
a substrate having a first conductivity type;
a first well having the first conductivity type;
a collector electrode having the first conductivity type in the first well;
a second well having a first concentration of a second conductivity type;
a first emitter electrode having the first conductivity type in the second well;
a base electrode having the second conductivity type in the second well;
a third well having a second concentration of the second conductivity type, wherein the second concentration is different from the first concentration; and
a second emitter electrode having the first conductivity type in the third well.
6. An image sensor, comprising:
a plurality of pixel circuits configured to operably sense an intensity of light to generate pixel signals; and
column and row selectors to select the pixel circuits to output the pixel signals as an image output signal;
wherein each of the pixel circuits includes:
a bipolar junction transistor (BJT) having a base, a collector, and a plurality of emitters, wherein the BJT is a phototransistor whose current generates the pixel signal for the corresponding pixel circuit;
a shutter control stage configured to operably control an exposure of the BJT;
a readout stage configured to operably read out the pixel signal; and
one or more switches configured to respectively control corresponding one or more of the plurality of emitters;
whereby the BJT has multiple selectable beta values by controlling the one or more switches.
7. The image sensor of claim 6 , wherein each of the pixel circuits further includes a storage device for storing the pixel signal.
8. The image sensor of claim 6 , wherein a total number of the switches corresponds to a total number of the emitters.
9. The image sensor of claim 6 , wherein a total number of the switches corresponds to a total number of the emitters minus one.
10. The image sensor of claim 6 , wherein the BJT is one semiconductor device including:
a substrate having a first conductivity type;
a first well having the first conductivity type;
a collector electrode having the first conductivity type in the first well;
a second well having a first concentration of a second conductivity type;
a first emitter electrode having the first conductivity type in the second well;
a base electrode having the second conductivity type in the second well;
a third well having a second concentration of the second conductivity type, wherein the second concentration is different from the first concentration; and
a second emitter electrode having the first conductivity type in the third well.