Low noise opamps without input diodes?

JFET amplifiers may be your best choice. LTC's LT1792 has only 4.2nV/rt-Hz typical and allows a wide differential swing, AFAICT. You didn't mention bandwidth requirements. BTW, you can make a composite two-opamp opamp to get the bandwidth you might need, and the input performance you need. OTOH, if you want superior performance and rock-bottom prices, remember, somebody has to pay the bills for the development of today's high-performance ICs.

That leaves out a lot of choices, next best thing to OPA from TI at least seems to be TLC070 etc I was going to suggest TLV274 wich I just used but looked up vn is 39nv the other chip I use is opa2354, I too needed to use them as comparators so no input diodes.

Colin =^.^=

Thanks, Win. It's a great amp. Unfortunately it seems to come only in singles and then the roughly $2.50 a pop begin to hurt. Ban suggested the OP467 which is a bit higher with its 6nv/rtHz but still not bad at all.

Bandwidth is low, a few kHz and mostly used as integrators, limiters etc.

This one doesn't have to be rock-bottom in cost, just reasonable. Of course I was quietly hoping there would be a supercharged TL084 somewhere for just a few pennies more :-)

Whoa! Now that's a great amp. Hadn't heard of it before. What makes me cringe though is that +/-15V supplies are now marketed as some kind of specialty "high voltage" feature. It used to be standard for all analog stuff (and as far as I'm concerned it still is).

robert

I am going to check out Phil's suggestion, the LM833. Best of all, that one is multi-sourced.

Mosfet and

Bipolar .

Bipolar has almost no change in input current. Thus the voltage drop across the input R's\ is no problem . Accurate .

MOSFETs have a extreme TEMPCO , thus their input Z is meaningless . It may as well be 50K ohm , to swamp out the extreme input current changes . They are 4 times higher B.W. .

Noise is very low in Bipolar OpAmps . But low noise is also very low B.W.

Have you noticed the old Bipolar Op Amps are still very useful ? MOSFETs did not obsolete Bipolars ..

Werty a écrit :

I can see you have very deep understanding of the subject. Sort of.

On Wed, 21 Mar 2007 22:09:33 +0100, in sci.electronics.design Fred Bartoli

ROFL, thanks Fred

martin

Yes I think I remember looking at that one once, but you talk of high-Z nodes, wont the bias current be a problem ?

If its not then there are a few more with not so low bias current on the TI list.

Colin =^.^=

Well, it doesn't exactly help, of course, but I may be able to live with If its not then there are a few more with not so low bias current on the TI

I'll have to go through it again. Any particular ones that come to mind? I rarely use low noise opamps since I design most of my stuff in discretes. Mainly to maintain true 2nd-sourcing for everything. Opamps are mostly relegated to more mundane jobs in my designs.

....

nop soz not without looking again, seem to remember the old ne5534... stil being there and making sure there are no hidden input diodes is a bit of a pain sometimes.

There are some improved lm358 types but these tend to have diodes. Ive got a couple of such types of op amps wich were usless for what I needed at the time becuase of input diodes but would otherwise do quite well for what you need.

Colin =^.^=

That one does have the diodes :-(

Diodes unfortunately disqualify the parts except for clean amplifier apps. But there I can easily design a low noise amp with discretes anyway.

this one ...

Colin =^.^=

That one would be good as well. Has diodes but these are zeners and one can usually live with the 10V differential they allow. However, the price is many times higher than for example the LM833.

Maxim makes a *comparator* with back-to-back input diodes. Talk about unclear on the concept!

John

ROFL! Luckily I have already had my morning coffee, else I'd be wiping off the monitor now.

You are NOISE .

There is nothing new in analogue Op Amps and there never will be .

The fast lane is to simply search existing , leading applications , and then merely buy what they used or compromise a bit to hit your target .

First you must duplicate that app'

Then mod circuit for your objective ----------------

Some ppl use a known fault in an I.C. to throw you off course . CD4___ . T.I. , long ago made CD4007 ? . If you held both CLK and RESET pins together , it did not act proper. Burr Brown Res' used this in an oscillator "722" and got burned ( Sole sourced = bad)

Thus , in your characterization of their application of that I.C. , you must consider this and purposely "push" the envelope , to learn if their are any anomolies , not mentioned in SPECs .

I do E.E. . I make profits .