US 7,486,322 B2
	Light sensor circuit having source/drain voltage changing-over circuit to minimize afterglow
Sukeyuki Shinotsuka, c/o 10 Banch 1, 1-chome, Shinsayama, Sayama-shi, Saitama (Japan); and Katsuhiko Takebe, c/o 10 Banch 1, 1-chome, Shinsayama, Sayama-shi, Saitama (Japan)
Appl. No. 10/471,522 PCT Filed Mar. 01, 2002, PCT No. PCT/JP02/01908 § 371(c)(1), (2), (4) Date Mar. 18, 2004, PCT Pub. No. WO02/073956, PCT Pub. Date Sep. 19, 2002.
Claims priority of application No. 2001-116117 (JP), filed on Mar. 09, 2001; application No. 2001-116119 (JP), filed on Mar. 09, 2001; and application No. 2001-180837 (JP), filed on May 11, 2001.
Prior Publication US 2004/0149889 A1, Aug. 05, 2004
Int. Cl. H04N 5/335 (2006.01); H04N 3/14 (2006.01); G01J 1/44 (2006.01)

U.S. Cl. 348—308  [250/214 L; 250/214.1; 348/294]

1 Claim

1. A light sensor circuit working by producing in a photoelectric converting element a photo current proportional to a quantity of light falling thereon and converting the photo current into a voltage signal by using a sub-threshold region characteristic of a transistor having a logarithmic output characteristic in a weak inverse state and outputting a sensor signal corresponding to the converted voltage signal, wherein said light sensor circuit is provided with a switching transistor for charging/discharging a parasite capacitor of the photoelectric converting element and an electric charge remaining in the parasite capacitor is removed by turning on the switching transistor before detecting a light signal by the photoelectric converting element, and wherein a turning-off voltage Vsw(off) of the switching transistor is expressed as Vsw(off)≤VG(Q1)−Vth(Q1)−Vth(Q4) wherein VG(Q1) is a gate voltage of the transistor for logarithmic characteristic conversion, Vth(Q1) is a threshold voltage of the transistor for logarithmic characteristic conversion and Vth(Q4) is a threshold voltage of the switching transistor.