Need help with designing transimpedance amplifier

[demodb]

transimpedance amplifier

He guys,

i'm currently doing a project in which i have to design a transimpedance amplifier. Maybe my question is a bit stupid but i'm a bit confused here. Do i have to design an amplifier which has a very high gain and just test this with an input voltage? And when i do have sufficient gain put it in a feedback topology, which makes it a transimpedance amplifier? Or do have to design an amplifier and test it with an input current?
Can anybody give me some hints here, i'm quit confused. Thx in advance...

 

[pixel]

Re: transimpedance amplifier

He guys,
i'm currently doing a project in which i have to design a transimpedance amplifier. Maybe my question is a bit stupid but i'm a bit confused here. Do i have to design an amplifier which has a very high gain and just test this with an input voltage? And when i do have sufficient gain put it in a feedback topology, which makes it a transimpedance amplifier? Or do have to design an amplifier and test it with an input current?
Can anybody give me some hints here, i'm quit confused. Thx in advance...

Yes you can do just like that. First design voltage amplifier, and then close loop and see TIA transient response and bandwidth.
For voltage amplifier you have to achieve enough bandwidth fa, which is defined by bitrate (>=1.4*0.7*bitRate). For that bandwidth optimize gain.
Then close loop with resistor Rf=a0/(pi*fa*Cd), where a0 is voltage amplifier gain at low freq, fa its bandwidth and and Cd photodiode capacitance.

What are your specifications?

 

[demodb]

Re: transimpedance amplifier

thx for your quick reply

i have to design an amplifier for a photo diode at a frequency of 3M [Hz]. The diode has a rise and fall time of 7.5n and a BW of 50M [Hz]. Its parasitic capacitance is 5p [F]. The current is dependant on the distance between transmitter and receiver, this varies from 8u to 80u [A].

The output is according TTL and needs to drive an inverter.

 

[pixel]

Re: transimpedance amplifier

Bitrate =3Mbit/s (not 3MHz)
Then make amplifier with bandwidth 3MHz, and optimize its dc gain a0, and use previous calculation for Rf.
You can also put some small capacitance in parallel with Rf if you need to stabilize it additionally. When you close loop TIA should have bandwidth od 2.4M (but not smaller). You may need automatic gain control if output voltage is too high for high currents.

 

[zorro]

transimpedance amplifier

Hi demodb,

Tha "gain" of an amplifier is g=Y/X, where Y and X are output and input respectively.
If g has dimension of an impedance, Y is a voltage and X a current. The "gain" is then a "trans"impedance.
A transimpedance amplifier converts current to voltage: Vout=Ztrans*Iin
It must have:
1) low input impedance; so the input current does not depend of the source impedance
2) low output impedance; so the output voltage does not depend of the load impedance
A way to get it is to use a voltage amplifier with node-node negative feedback, i.e. for example an operational amplifier with an impedance as feedback.
Another way is without feedback, desgning an amplifier with the above characteristics and the desired ratio Ztrans.
The advantages of feedback are that you can get very high Zin and very low Zout, and the “gain” (transimpedance) depends of passive components.
The drawbacks of feedback are that it can be difficult to get very high bandwidth and stability.
Regards

Z

 

[artem]

transimpedance amplifier

have a look to :

**broken link removed**