Jfet folded cascode with diamond buffer opamp

sonnya · 21st May 2011, 12:22 PM

Hi all.

Well i thought it was time to do some new stuff.

So my first attempt is to make an opamp replacement with jfet inputs.

I will try to hit the 700x700mil size for this one.

This will be fun.

The jfet has an input noise level of 6nV so it will be able to be used for riaa as well as linelevel.

I have attached the diagram. I expect to have the board ready by tomorrow.

jam · 01:17 PM

Hi Sonnya,

Nice circuit.

Question . Does cascoding the folded cascode help much? I would think it's use in this application would be minimal but I could be wrong.
I like the use of the Wilson Mirror which I believe is far better than the Widlar that is often used.

Keep up the good work.

Regards,

Jam

sonnya · 22nd May 2011, 03:04 AM

Hi Jam.

Thanks for the comment.

The widlar currentsource is made for the silicon process as it is not possible to make high ohm resistors in the silicon. By adding the resistor in "mirror" transistor it is possible to compensate for it. Correct me if i am wrong.

I can see that i maybee has been "blinded" by the use of folded cascode as i have used them before.

I would be easy to replace it by two wilson mirror and it would require the same or less transistor. It would actually raise the impedance in the tranconductance stage, like i wanted it to.

So i will change that part. thanks for the guiding question.

jam · 03:31 AM

Sonnya,

Actually I like the four transistor Wilson Mirror (Still might be a bit of overkill).
I will not disagree with you that the folded cascode can sound very good and only requires matching of the diff and current mirror offers equal pull-up and pull-down. All in all a very elegant circuit.

sonnya · 22nd May 2011, 03:35 AM

Yes i know it, but i think i will not be able to get it down onto 700x700mil board. It is already a plenty booked board.

jam · 22nd May 2011, 03:38 AM

Sonnya, if you are making boards I would like to purchase a few if possible......so would a few other members, I bet.

Regards.

Jam

sonnya · 22nd May 2011, 12:23 PM

Here it is.

The size of the module is 800x800mil or 20.32x20.32mm.

More info will come.

Bonsai · 24th May 2011, 02:56 AM

Sonnya, have you simmed it to see what the performance is like? Looks like a an interesting circuit.

sonnya · 25th May 2011, 05:27 AM

I will sim it this weekend.

mlloyd1 · 27th May 2011, 05:05 AM

indeed ...

mlloyd1

Quote:

Originally Posted by jam

Sonnya, if you are making boards I would like to purchase a few if possible ...... so would a few other members, I bet.

Regards.

Jam

21st May 2011, 01:15 PM	#2
jam diyAudio Member Join Date: May 2001 Location: Charlotte,NC,USA	Hi Sonnya, Nice circuit. Question . Does cascoding the folded cascode help much? I would think it's use in this application would be minimal but I could be wrong. I like the use of the Wilson Mirror which I believe is far better than the Widlar that is often used. Keep up the good work. Regards, Jam Last edited by jam; 21st May 2011 at 01:17 PM.

24th May 2011, 02:56 AM	#8
Bonsai diyAudio Member Join Date: Aug 2006 Location: Taipei, Taiwan	Sonnya, have you simmed it to see what the performance is like? Looks like a an interesting circuit. __________________ bonsai http://www.hifisonix.com/

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22nd May 2011, 03:04 AM	#3
sonnya diyAudio Member Join Date: Oct 2001 Location: Denmark	Hi Jam. Thanks for the comment. The widlar currentsource is made for the silicon process as it is not possible to make high ohm resistors in the silicon. By adding the resistor in "mirror" transistor it is possible to compensate for it. Correct me if i am wrong. I can see that i maybee has been "blinded" by the use of folded cascode as i have used them before. I would be easy to replace it by two wilson mirror and it would require the same or less transistor. It would actually raise the impedance in the tranconductance stage, like i wanted it to. So i will change that part. thanks for the guiding question.

22nd May 2011, 03:35 AM	#5
sonnya diyAudio Member Join Date: Oct 2001 Location: Denmark	Yes i know it, but i think i will not be able to get it down onto 700x700mil board. It is already a plenty booked board.

22nd May 2011, 03:38 AM	#6
jam diyAudio Member Join Date: May 2001 Location: Charlotte,NC,USA	Sonnya, if you are making boards I would like to purchase a few if possible......so would a few other members, I bet. Regards. Jam

25th May 2011, 05:27 AM	#9
sonnya diyAudio Member Join Date: Oct 2001 Location: Denmark	I will sim it this weekend.

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