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AD8015 TIA Questions

Question asked by lriobo on Dec 21, 2015
Latest reply on Dec 24, 2015 by lriobo

Hello There.

I'm designing a Transimpedance amplifier for the measurement of sinusoidal optical signals in the 500nm and 700nm wavelength range, with a BW >= 50MHZ.

Looking for high speed amplifiers, i came across with AD8015 and i have some questions on the operation of this amplifier:

 

1 - How the entire photodiode+amplifier bandwidth depends of the capacitance of the photodiode? In the datasheet, there is an application example with a photodiode with a capacitance of 0,7pF, but there is an equation BW = 1/2pi*3393*C1, where C1 is a capacitor connected in the 4 and 8 pins and to Vs+ (in Fig. 3), but if i use a photodiode with a bigger capacitance (1 o 2 pF, always thinking of the BW>= 50MHZ requierement), the BW calculation is BW = 1/2pi*3393*(C1+Cphotodiode)?

 

2 - Fig. 14 plots Differential Gain vs. Input Capacitance. What is this "input Capacitance"? Cphotodiode? C1? Because That plot doesn't respond to BW = 1/(2pi*3393*C1)

 

 

Thank you!

 

Lucas.

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