OPA141: How to design a transimpedance amplifier

August Joseph

Part Number: OPA141
Other Parts Discussed in Thread: LM7705, LMP7721, OPA320, OPA325

How to design a transimpedance amplifier using opa141? I put the cathode of the photodiode at the inverting terminal, grounded the anode and grounded the non-inverting terminal. Single supply of 5v was given. Feedback resistor= 27k ohm, feedback capacitor= 1uf, using transimpedance amplifier equations. How to measure the gain of transimpedance amplifier? How to measure the photocurrent?

over 5 years ago

0 kai klaas69 over 5 years ago

Guru 140200 points

Hi August,

the OPA141 cannot fully go down to 0V at its output. See the "voltage output" specification on page 5 of datasheet. So, either you choose another OPAmp which can go down to 0V a bit closer or you apply a negative supply voltage to the V- pin of OPA141. Eventually, it's sufficient to take the LM7705 for this purpose.

Kai

0 Michael Steffes over 5 years ago

Guru 48395 points

you might look at the LMP7721, also - I did write an old Electronic Design article on testing transimpedance stages - just looked and all the figures are gone - I am sure I have a print copy if you want me to scan that and attach. Your feedback of 1uF gives only 6Hz you know. also, what is the PD capacitance.

0 August Joseph over 5 years ago in reply to Michael Steffes

Prodigy 70 points

Thanks, Michael...

The PD capacitance is 65pf. The signals to be obtained are below 20Hz. And please we would like to get a scan copy of your article!

0 August Joseph over 5 years ago in reply to kai klaas69

Prodigy 70 points

Thanks Kai,

Is it better to apply -ve voltage at V- pin or choose another amplifier like LM7705? Is LM7705 the best option for transimpedance amplifier? We want output signals of less than 20Hz

August

0 kai klaas69 over 5 years ago in reply to August Joseph

Guru 140200 points

Hi August,

the LM7705 is just a comfortable way to power the OPAmp with a negative supply voltage, because the negative voltage is produced from the positive supply voltage. Please have a look into the datasheet of LM7705.

Kai

0 August Joseph over 5 years ago in reply to kai klaas69

Prodigy 70 points

Oh yes, thanks Kai. Didn't go through the datasheet before answering. Also, is OPA141 the best option for transimpedance amplifier for signals less than 20Hz?

August

0 kai klaas69 over 5 years ago in reply to August Joseph

Guru 140200 points

Hi August,

I wouldn't choose the OPA141. The LMP7721, as suggested by Michael, has a lower input offset voltage and its output can go further down to 0V.

Kai

0 Michael Steffes over 5 years ago in reply to kai klaas69

Guru 48395 points

Low frequency Zt with LMP7721.docxHello Joseph,

I ran some tests with the LMP7721 in the attached file, I also attached the TINA files, 10Hz is really low F, could use a much lower speed part if you wanted to - or comp this one flat using 7pF and get 1Mhz flat out of this stage and postfilter? That would be a good place for an active filter if this is perhaps test equipment.

LMP7721 27k transimpedance.TSC

LMP7721 27k transimpedance test.TSC

0 Thomas Kuehl over 5 years ago

TI__Guru* 93105 points

Hi August,

It appears that you have much to learn about photodiodes and transimpedance amplifiers. I am going to provide you a TI presentation on the subjects that one of our rotation engineers from China developed several years back. It provides a good deal of information from the basics to more complex subjects. I think if you study the material you will be able to answer your questions yourself.

Kai brings up a good point regarding the OPA141 output level when used with a single, +5 V supply. If you can't include the LM7705, then I suggest using one of our single supply CMOS op amps such as the OPA325, or OPA320, for the application. The output still won't get to exactly 0 V, with a single supply but closer than you will get with most HV op amps. The op amp can be more precisely selected once you have your basic circuit designed.

Regards, Thomas

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OPA141: How to design a transimpedance amplifier