Linda Y Liu

US Patent:

6930300, Aug 16, 2005

Filed:

Jul 30, 2002

Appl. No.:

10/209452

Inventors:

Darin James Douma - Monrovia CA, US
Philip D. Shapiro - Palo Alto CA, US
Linda Xiaorong Liu - San Jose CA, US

Assignee:

Finisar Corporation - Sunnyvale CA

International Classification:

H01J040/14

US Classification:

250214A, 250214 R

Abstract:

The method and apparatus for monitoring a photo-detector generates a highly compliant mirror current across a broad range of photo-detector current levels. The apparatus for monitoring includes: a pair of bipolar transistors and a first non-linear isolation element. The pair of transistors are connected in a mirror configuration with a sense transistor one of the pair of transistors sensing a photo-detector current and with a mirror transistor one of the pair of transistors mirroring the photo-detector current with a mirror current. The first non-linear isolation element has at least two terminals a first of which couples to the collector of the mirror transistor. The first non-linear isolation element exhibits a non-linear voltage drop between the at least two terminals in response to varying levels of the mirror current to improve compliance between the mirror current and the detector current. Methods and means for monitoring a photo-detector are also disclosed.