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Q&A Choosing between common-drain JFET amplifier, and common-source

Do common-source JFET amplifiers have an advantage over common-drain? The JFET would be in a low noise photodiode amplifier. The signal is 100us pulses with 10us raise times. Here are the schema...

1 answer  ·  posted 1y ago by misk94555‭  ·  last activity 1y ago by Olin Lathrop‭

Question JFET photodiode
#2: Post edited by user avatar misk94555‭ · 2023-07-07T02:41:21Z (over 1 year ago)
I fixed the wrong photodiode polarity, which Olin and Andy pointed out.
  • Do common-source JFET amplifiers have an advantage over common-drain? The JFET would be in a low noise photodiode amplifier. The signal is 100us pulses with blunted raise times.
  • Here are the schematics which I have in mind.
  • The op-amp would be [LTC6252](https://www.analog.com/en/products/ltc6252.html) or [LT6200](https://www.analog.com/en/products/lt6200.html). Single-supply operation is desirable for me.
  • <h3>Common-drain</h3>
  • ![Schematic snippet. Common-drain photodiode amplifier consisting of a JFET and and operational amplifier.](https://electrical.codidact.com/uploads/d4ebrubqtugqsrpicbgyavzlfktw)
  • I picked up this common-drain idea from the [LT6200 datasheet](https://www.analog.com/en/products/lt6200.html) (application example on the first page).
  • Common-drain JFET has a prototyping appeal, because it would be easy to try a simple transimpedance op-amp (without a JFET) on the same PCB. Fallback position.
  • <h3>Common-source</h3>
  • ![Schematic snippet. Common-source photodiode amplifier consisting of a JFET and and operational amplifier.](https://electrical.codidact.com/uploads/o9wbn6zf1525d212018zkq3vqoox)
  • I picked up this common-source idea from [this app note](https://www.analog.com/en/technical-articles/low-noise-single-supply-photodiode-amplifier.html).
  • Do common-source JFET amplifiers have an advantage over common-drain? The JFET would be in a low noise photodiode amplifier. The signal is 100us pulses with 10us raise times.
  • Here are the schematics which I have in mind.
  • The op-amp would be [LTC6252](https://www.analog.com/en/products/ltc6252.html) or [LT6200](https://www.analog.com/en/products/lt6200.html). Single-supply operation is desirable for me.
  • <h3>Common-drain</h3>
  • ![Schematic snippet. Common-drain photodiode amplifier consisting of a JFET and and operational amplifier.](https://electrical.codidact.com/uploads/1bhplw7pepkpz7wslxel3ak3xcbr)
  • I picked up this common-drain idea from the [LT6200 datasheet](https://www.analog.com/en/products/lt6200.html) (application example on the first page).
  • Common-drain JFET has a prototyping appeal, because it would be easy to try a simple transimpedance op-amp (without a JFET) on the same PCB. Fallback position.
  • <h3>Common-source</h3>
  • ![Schematic snippet. Common-source photodiode amplifier consisting of a JFET and and operational amplifier.](https://electrical.codidact.com/uploads/iuu59r8sgc6ew4qpjt1t3aog72sr)
  • I picked up this common-source idea from [this app note](https://www.analog.com/en/technical-articles/low-noise-single-supply-photodiode-amplifier.html).
#1: Initial revision by user avatar misk94555‭ · 2023-07-03T18:07:23Z (over 1 year ago) 
Choosing between common-drain JFET amplifier, and common-source
Do common-source JFET amplifiers have an advantage over common-drain?  The JFET would be in a low noise photodiode amplifier.  The signal is 100us pulses with blunted raise times.  

Here are the schematics which I have in mind.  
The op-amp would be [LTC6252](https://www.analog.com/en/products/ltc6252.html) or [LT6200](https://www.analog.com/en/products/lt6200.html).  Single-supply operation is desirable for me.

<h3>Common-drain</h3>

![Schematic snippet.  Common-drain photodiode amplifier consisting of a JFET and and operational amplifier.](https://electrical.codidact.com/uploads/d4ebrubqtugqsrpicbgyavzlfktw)
I picked up this common-drain idea from the [LT6200 datasheet](https://www.analog.com/en/products/lt6200.html) (application example on the first page).

Common-drain JFET has a prototyping appeal, because it would be easy to try a simple transimpedance op-amp (without a JFET) on the same PCB. Fallback position.

<h3>Common-source</h3>

![Schematic snippet.  Common-source photodiode amplifier consisting of a JFET and and operational amplifier.](https://electrical.codidact.com/uploads/o9wbn6zf1525d212018zkq3vqoox)
I picked up this common-source idea from [this app note](https://www.analog.com/en/technical-articles/low-noise-single-supply-photodiode-amplifier.html).
JFET photodiode