PIN photodiode & TIA question

[Roman D. Sinjuk]

Hi everybody.

I am going to use S7481 photodiode as high speed photodetector for 100Mbit/s
free space optical link. It is high speed photodiode (Cut-off frequency 500MHz)
with high sensitivity in visible range (http://jp.hamamatsu.com/resources/products/ssd/pdf/s6431_etc_kpin1018j03.pdf),
but it has high junction capacitance - 6pF. I have MAX3657 transimpedance
amplifier (TIA) (http://pdfserv.maxim-ic.com/en/ds/MAX3657.pdf).
But it optimized for 0.5pF capacitance photodiodes. For 0.5pF MAX3657 has
130MHz signal bandwidth, for 1.5pF bandwidth is 50MHz. It less than 75Mhz,
needed for 100Mbit/s. Not only bandwidth decreased, input referred noise level
increase also.

Can I loss sensitivity but reach 75Mhz bandwidth on S7481 + MAX3657?
Or I need other solution ? What would you recommend ?

 

[Phil Hobbs]

Hi everybody.

I am going to use S7481 photodiode as high speed photodetector for 100Mbit/s
free space optical link. It is high speed photodiode (Cut-off frequency 500MHz)
with high sensitivity in visible range (http://jp.hamamatsu.com/resources/products/ssd/pdf/s6431_etc_kpin1018j03.pdf),
but it has high junction capacitance - 6pF. I have MAX3657 transimpedance
amplifier (TIA) (http://pdfserv.maxim-ic.com/en/ds/MAX3657.pdf).
But it optimized for 0.5pF capacitance photodiodes. For 0.5pF MAX3657 has
130MHz signal bandwidth, for 1.5pF bandwidth is 50MHz. It less than 75Mhz,
needed for 100Mbit/s. Not only bandwidth decreased, input referred noise level
increase also.

Can I loss sensitivity but reach 75Mhz bandwidth on S7481 + MAX3657?
Or I need other solution ? What would you recommend ?

I have an article on my web site that has this, with detailed design steps.

http://www.pergamos.net, about halfway down.

Cheers,

Phil Hobbs