High speed amplifier ??

Hi, I am a student of Northwestern Polytechnical University in China. I want to use a photodiode (AEPX65:Responsivity 0.35A/W,Dark Current

2nA,NEP 6.8e-14WHz-½,Capacitance 6pF,Risetime 1ns) to receive about 10nsec wide pulses but low intensity about 10e-6mJ,then the output current is converted to voltage by an amplifier circuit,the voltage signal is transmitted to the oscilloscope (Tektronix 100 MHz BW,1 GS/s Sample Rate) so that to dispaly the pulse wave.Now I have the photodiode and the oscilloscope, but I don't know which amplifier is suitable.OPA657? EL2075?maybe other more suitable? And I else don't know how to design the voltage feedback circuit. If someone has some suggestion or some schematic, it would be great.Hoping to hear from you soon. Thank you in advance

Jiang Yajun Myemil: snipped-for-privacy@mail.nwpu.edu.cn

By '10e-6mJ' do you mean 10 nJ or 1 nJ? Either way, those pulses are

*huge*, with peak currents of 350 mA or 35 mA. You're going to saturate that poor photodiode completely. In any case, you won't need an amplifier: just connect the PD cathode to a +5V supply through a 1k resistor, connect a 47 nF capacitor between the PD cathode and the centre conductor of a piece of coax, and connect the coax shield and power supply common terminal to the PD anode. Then put a neutral density filter in front of the poor photodiode to knock the peak current down to 1 or 2 mA. Use the 50-ohm input setting on the scope.

Your pulses will be 50 or 100 mV tall, easily seen on the 10 mV/div range. If you want more signal, any fast amplifier is fine--you don't need an OPA657. A Mini-Circuits MMIC amp is a good possibility. Keep the impedance levels low, because this isn't a low-light application.

(In fact if the duty cycle were high enough you could easily power the amplifier off those pulses!)

Cheers,

Phil Hobbs