Device for receiving light used in CCD image sensor or the like

• US 5,650,643 A
• Filed: 03/21/1995
• Issued: 07/22/1997
• Est. Priority Date: 03/30/1994
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Konuma, Kazuo
• Primary Examiner(s): Thomas, Tom
• Assistant Examiner(s): WILLIAMS, ALEXANDER O
• Application Number:
  US08/408,032
• Time in Patent Office: 854 Days
• Field of Search: 257/222, 257/443, 257/233, 257/223, 257/225, 257/226, 257/227, 257/228, 257/229, 257/239, 257/444, 257/80, 257/83, 257/84, 348/297, 348/302, 348/307, 348/308, 348/310, 348/294, 348/221, 348/228, 348/229, 348/230
• US Class Current: 257/225
• CPC Class Codes: G01J 1/46 using a capacitor
• CPC Class Codes: H04N 25/53 Control of the integration time
• CPC Class Codes: H04N 25/772 comprising A/D, V/T, V/F, I/T or I/F converters
• CPC Class Codes: H04N 25/78 Readout circuits for addressed sensors, e.g. output amplifiers or A/D converters

Abstract

A light receiving device includes, in addition to a photodiode and a reset element, a comparator formed by a first and a second MOS transistor and a counter. The comparator compares an output potential of the photodiode applied to a gate electrode of the first MOS transistor with a threshold potential externally applied to a gate electrode of the second MOS transistor. The counter counts a time duration from a point of time when the photodiode is reset by the switching element to a point of time at which the output potential of the photodiode exceeds the threshold potential, and outputs the time duration in a numeral value corresponding to the quantity of light incident on the photodiode. The required light sensitivity can be maintained even when the quantity of light is either large or small. Also, non-destructive reading can be carried out.

Claims

1. A light receiving device comprising:

a photodiode, having spectral-response characteristics that change depending on a reverse bias state, for both photoelectric conversion and electron charge accumulation, said photodiode being maintained in a floating state after said reverse bias is reset;

a switching element for periodically providing a reverse bias resetting potential to said photodiode;

a comparator for comparing a potential of said photodiode with a threshold potential corresponding to predetermined spectral-response characteristics; and

a counter for counting a time duration from when said photodiode is reset by said switching element to when the potential of said photodiode exceeds said threshold potential, and outputting the time duration as a numerical value corresponding to a quantity of light incident on said light receiving device.

2. A method for driving a light receiving device having a comparator and a counter, in which a reverse bias reset potential is provided to a photodiode by periodically applying a reset potential to said photodiode and during a time period from immediately after a provision of a first reset potential to a time when a next reset potential is provided, said photodiode receives light and is maintained in a floating state and undergoes a reverse bias attenuation change operation responsive to quantities of received light, said method comprising steps of:

providing a threshold potential to said comparator;

inputting, to said comparator, an output potential of said photodiode;

inputting an output of said comparator to said counter;

counting a time duration from when said first reset potential is provided to when said output potential of said photodiode equals said threshold potential; and

outputting said time duration as numerical value each time said reset potential is provided,

said counting of the time duration being carried out by counting a number of pulses of a master clock inputted to a clock input terminal of said counter, and

said potential of the photodiode and said threshold potential being compared non-destructively at a plurality of levels whereby spectral-response characteristics of the light incident on said light receiving device are obtained.