| US 7,605,359 B2 | ||
| Light source frequency detection circuit for image sensor | ||
| Tiejun Dai, Sunnyvale, Calif. (US); Jingzhou Zhang, Santa Clara, Calif. (US); and Liping Deng, Cupertino, Calif. (US) | ||
| Assigned to OmniVision Technologies, Inc., Santa Clara, Calif. (US) | ||
| Filed on Sep. 14, 2007, as Appl. No. 11/901,212. | ||
| Prior Publication US 2009/0072126 A1, Mar. 19, 2009 | ||
| Int. Cl. H01J 40/14 (2006.01); G01J 1/18 (2006.01) | ||
| U.S. Cl. 250—214R [250/214 LS; 250/208.1; 348/226.1; 348/228.1] | 18 Claims |
| 1. An apparatus for determining a power frequency of a light source, the apparatus comprising:
a photo-sensor coupled to generate an electrical signal responsive to light incident thereon;
a modulator circuit coupled to the photo-sensor to generate a modulated signal based on the electrical signal that toggles
at a rate substantially proportional to the power frequency of the light source; and
a logic unit coupled to the modulator circuit to determine a toggling frequency of the modulated signal and to generate a
frequency select signal indicating the power frequency of the light source,
wherein the modulator circuit comprises:
a comparator including first and second comparator inputs and a comparator output, the first comparator input coupled to the
photo-sensor and the second comparator input coupled to receive a reference signal; and
a charging source coupled to selectively charge the first comparator input in response to the comparator output.
|