Leakage current compensating circuit for semiconductor image sensor

Claim 2

In combination with image sensor means producing a sensor signal comprising a video current signal proportional to the level of light received by the image sensor and a leakage current signal proportional to the temperature of the image sensor means, a circuit comprising: first circuit means responsive to thermal energy from the image sensor means for producing a compensating current signal proportional to said leakage current signal; and second circuit means connected to said first circuit means and the image sensor means for offsetting the leakage current signal with the compensating current signal, said second circuit means comprising a current node and a field effect transistor having its source connected to said node, the source current of said field effect transistor being proportional to said sensor signal, said current node summing said compensating current signal and said source current of said field effect transistor, said leakage current signal and said compensating current signal flowing in different directions relative to said current node whereby an output signal results which is proportional only to the level of light received by the image sensor means.

Claim 3

In combination with an image sensor means producing a sensor signal comprising video current signal proportional to the level of light received by the image sensor and a leakage current signal proportional to the temperature of the image sensor means, a circuit comprising: a summing circuit comprising a current node and a field effect transistor having its source connected to said node, the source current of said field effect transistor being proportional to said sensor signal; a compensating current circuit having its output connected to said current node, said compensating current circuit comprising diode means having a constant temperature relationship with said image sensor for producing a leakage current signal proportional to the temperature of said image sensor for producing a leakage current signal proportional to the temperature of said diode means, said diode means being reverse biased; curcuit means connected to the diode means and the image sensor for subtracting the diode means leakage current signal from the image sensor signal where an adjustable gain amplifier having an adjustable feedback loop, said adjustable gain amplifier being connected to said diode means; means connecting the output of said image sensor means to the gate of said field effect transistor; and an output circuit means connected to said current node for providing a voltage output signal proportionAl only to the level of light received by said image sensor.

Claim 4

In combination with an image sensor means producing a sensor signal comprising video current signal proportional to the level of light received by the image sensor and a leakage current signal proportional to the temperature of the image sensor means, a circuit comprising: a summing circuit comprising a current node and a field effect transistor having its source connected to said node, the source current of said field effect transistor being proportional to said sensor signal; a compensating current circuit having its output connected to said current node, said compensating current circuit comprising diode means having a constant temperature relationship with said image sensor for producing a leakage current signal proportional to the temperature of said image sensor for producing a leakage current signal proportional to the temperature of said diode means, said diode means being reverse biased; curcuit means connected to the diode means and the image sensor for subtracting the diode means leakage current signal from the image sensor signal where an adjustable gain amplifier having an adjustable feedback loop, said adjustable gain amplifier being connected to said diode means; means connecting the output of said image sensor means to the gate of said field effect transistor; and an output circuit means connected to said current node for providing a voltage output signal proportionAl only to the level of light received by said image sensor.

Claim 5

The circuit as set forth in claim 2 wherein said summing circuit further comprises a resistor, said resistor being connected between the drain of said field effect transistor and ground potential and wherein said compensating current circuit further comprises a transistor connected in the output circuit of said compensating current circuit, the output of said adjustable gain amplifier being connected to the emitter of said transistor.

Claim 6

The circuit set forth in claim 2 wherein said output circuit comprises a transistor and a resistor, said transistor having its emitter connected to said current node, it''s base connected to a ground potential and it''s collector connected to a first end of said resistor and as the output of said output circuit.

Claim 7

The circuit as set forth in claim 2 wherein said means connecting the output of said image sensor means to the gate of said field effect transistor comprises an amplifier, a transistor, a capacitor and a resistor, said amplifier having it''s input connected to said output of said image sensor means and a first end of said resistor and it''s output connected through said caacitor to said transistor and said gate of said field effect transistor.

Claim 8

The circuit as set forth in claim 2 wherein said summing circuit further comprises a first resistor, said first resistor being connected between the drain of said field effect transistor and ground potential; wherein said compensating current circuit further comprises a first transistor connected in the output circuit of said compensating current circuit, the output of said adjustable gain amplifier being connected to the emitter of said first transistor; wherein said output circuit comprises a second transistor and a first resistor, said second transistor having it''s emitter connected to said current node, it'' s base connected to a ground potential and it''s collector connected to a first end of said resistor and as the output of said output circuit; and wherein said means connecting the output of said image sensor means to the gate of said field effect transistor comprises an amplifier, a second transistor, a capacitor and a second resistor, said amplifier having it''s input connected to said output of said image sensor means and a first end of said resistor and it''s output connected through said capacitor to said second transistor and said gate of said field effect transistor.

Claim 9

The circuit as set forth in claim 6 wherein said first transistor and said second transistor are switched in synchronism with the electron beam of said image sensor to supress said sensor signal output and said leakage current signal during the return interval of the electron beam of said image sensor.

Claim 10

A dark current compensating circuit for use with an image sensor and producing a sensor current signal having a video current component proportional to the level of light received by the image sensor and a dark current component comprising the image sensor leakage current and being proportional to the temperature of the image sensor, said circuit comprising: a diode positioned in thermal contact with said image sensor and being reverse biased, said diode having a leakage current signal proportional to its temperature; and circuit means connected to the image sensor and the diode and receiving the sensor current signal and the diode leakage current signal from different electrical directions for summing the sensor current signal and the diode leakage current signal whereby the diode leakage current compensates for the effect of the dark current.

Claim 11

A dark current compensating circuit for use with an image sensor and producing a sensor current signal having a video current component proportional to the level of light received by the image sensor and a dark current component comprising the image sensor leakage current and being proportional to the temperature of the image sensor, said circuit comprising: a diode positioned in thermal contact with said image sensor and being reverse biased, said diode having a leakage current signal proportional to its temperature; and circuit means connected to the image sensor and the diode and receiving the sensor current signal and the diode leakage current signal from different electrical directions for summing the sensor current signal and the diode leakage current signal whereby the diode leakage current compensates for the effect of the dark current.

Claim 12

The combination according to claim 8 wherein said diode and the image sensor each have the same leakage current-temperature characteristic.