Design a TIA with beloe requirements

Phil Hobbs

2016-08-27 19:54:51 UTC

Post by i***@gmail.com
Hello experts,
well..am new to this field and I was given a task of designing a
trans impedance amplifier to detect low currents of the APD ranging
from 0 to 15uA.. It looks simple to go ahead but the design
requirements threw plenty of challenges and brought me here..
Here are my design requirements: Photodoide: Avalanche Photo-diode
with 5pF input capacitance and 50nA dark current, R=0.9 with gain
multiplication factor,20....
It is biased such that cathode is connected to +28V and anode, to
the input terminal of the opamp...
Opamp: Must be a single supply (+5 V) and detect currents upto 12uA
and required bandwidth is 1MHz......
So how can I use an inverting configuration with single supply
positive voltage? Which opamp suits for this? I tried providing
biasing voltage at non-inverting terminal of the opamp in inverting
configuration but DC level was keep varying. How can I use an
inverting configuration for this

Well, you could bias the noninverting input at, say, 4V and work down
from there. The second stage (also inverting) would do the level
translation back down to near ground. It's usually wise to use a
nonzero bias level in single supply circuits in any case.

Post by i***@gmail.com
The next stage of this TIA is a HPF combined with a LPF (again
single supply opamps and use Sallenkey topology- purpose is to limit
the bandwidth strictly to the 80kHz to 1MHz)..so I can either
distribute the overall gain or a single stage does the job... Which
one will be the best option to go with?

You need a pretty good op amp for that 1-MHz lowpass. You might want to
consider a BJT emitter follower with a DC restore loop wrapped round it.

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net