Low noise amplifier for passive pixel CMOS imager
First Claim
1. A CMOS passive pixel sensor system, comprising:
- a pixel comprising a photodetector connected to an access transistor;
a capacitive transimpedance amplifier (CTIA) having a CTIA input and a CTIA output;
an electrical bus connecting said pixel to said CTIA input;
a reset switch and a selectable feedback capacitance connected in parallel from said CTIA input to said CTIA output;
a selectable load capacitance connected to said CTIA output;
a first correlated double sampling circuit connected to said load capacitance;
a sample-and-hold buffer circuit connected to said first correlated double sampling circuit; and
an offset cancellation circuit connecting said buffer circuit to an output bus.
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Accused Products
Abstract
A CMOS imaging system provides low noise read out and amplification for an array of passive pixels, each of which comprises a photodetector, an access MOSFET, and a second MOSFET that functions as a signal overflow shunt and a means for electrically injecting a test signal. The read out circuit for each column of pixels includes a high gain, wide bandwidth, CMOS differential amplifier, a reset switch and selectable feedback capacitors, selectable load capacitors, correlated double sampling and sample-and-hold circuits, an optional pipelining circuit, and an offset cancellation circuit connected to an output bus to suppress the input offset nonuniformity of the amplifier. For full process compatibility with standard silicided submicron CMOS and to maximize yield and minimize die cost, each photodiode may comprise the lightly doped source of its access MOSFET. Circuit complexity is restricted to the column buffers, which exploit signal processing capability inherent in CMOS. Advantages include high fabrication yield, broadband spectral response from near-UV to near-IR, low read noise at HDTV data rates, large charge-handling capacity, variable sensitivity with simple controls, and reduced power consumption.
265 Citations
20 Claims
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1. A CMOS passive pixel sensor system, comprising:
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a pixel comprising a photodetector connected to an access transistor; a capacitive transimpedance amplifier (CTIA) having a CTIA input and a CTIA output;
an electrical bus connecting said pixel to said CTIA input;a reset switch and a selectable feedback capacitance connected in parallel from said CTIA input to said CTIA output; a selectable load capacitance connected to said CTIA output; a first correlated double sampling circuit connected to said load capacitance; a sample-and-hold buffer circuit connected to said first correlated double sampling circuit; and an offset cancellation circuit connecting said buffer circuit to an output bus. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A readout circuit for a CMOS passive pixel sensor system, comprising:
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a plurality of pixels connected to an input bus, each of said pixels comprising a photodetector, an overflow transistor connected to said photodetector, and an access transistor connecting said photodetector to said input bus; a high gain, wide bandwidth, CMOS differential amplifier having a first input connected to said input bus, a second input connected to a low noise reference, and an amplifier output; a reset switch and a feedback capacitance connected in parallel from said input bus to said amplifier output; a selectable load capacitance connected to said amplifier output; a first correlated double sampling circuit connected to said load capacitance; a sample-and-hold buffer circuit connected to said first correlated double sampling circuit; an offset cancellation circuit connected to an output bus; and a pipeline circuit having at least two parallel branches connecting said buffer circuit to said offset cancellation circuit. - View Dependent Claims (12, 13, 14, 15)
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16. A CMOS column readout circuit for an array of passive pixels, comprising:
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a column bus connecting a column of said pixels to the readout circuit; each of said column pixels comprising an access transistor connected to said column bus, a lightly doped source region of said access transistor forming a photodiode, and an overflow transistor connected to said photodiode; a capacitive transimpedance amplifier (CTIA) comprising a high gain, wide bandwidth, CMOS differential amplifier having a first input connected to said column bus, a second input connected to a low noise reference, and an amplifier output; said CTIA including a reset switch and a selectable feedback capacitance connected in parallel between said first amplifier input and said amplifier output; a selectable load capacitance connected to said amplifier output; a first correlated double sampling circuit connected to said load capacitance; a sample-and-hold buffer circuit connected to said first correlated double sampling circuit; an offset cancellation circuit connected to an output bus; and a pipeline circuit having at least two parallel branches connecting said buffer circuit to said offset cancellation circuit, each of said parallel branches of said pipeline circuit includes a second correlated double sampling circuit. - View Dependent Claims (17, 18, 19, 20)
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Specification