Maker Pro
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Low noise opamps without input diodes?

J

Joerg

Jan 1, 1970
0
The OPA series seems hard to buy these days and I've heard rumors of
some difficulties. So, I am looking for non-OPA varieties:

<5nV/rtHz would be nice. +/-15V supplies. No back-to-back diodes on the
inputs like the AD8674 has, need to use some of them as comparators and
trackers. Can't easily buffer and they must track some high-Z nodes. I
don't need the full VEE to VDD swing but at least 5V differential or so.
 
B

Ban

Jan 1, 1970
0
Joerg said:
The OPA series seems hard to buy these days and I've heard rumors of
some difficulties. So, I am looking for non-OPA varieties:

<5nV/rtHz would be nice. +/-15V supplies. No back-to-back diodes on
the inputs like the AD8674 has, need to use some of them as
comparators and trackers. Can't easily buffer and they must track
some high-Z nodes. I don't need the full VEE to VDD swing but at
least 5V differential or so.

Yes, there are some...
shit, I remember you were boycotting National and Phillips because of their
fancy websites, they are cheaper, but what to do! Maxim and LT also -cazzo,
there they go
then maybe AD? ADA4004, OP467
Otherwise just thow together some discretes, because those mentioned are
above 80c.
 
J

Joerg

Jan 1, 1970
0
Ban said:
Yes, there are some...
shit, I remember you were boycotting National and Phillips because of their
fancy websites, they are cheaper, but what to do! Maxim and LT also -cazzo,
there they go


I had checked National (via Digikey because this time they really goofed
their web site...), Philips and LT. Didn't find much there. Maxim is the
only one I didn't check because clients had too many "can't deliver for
first production run" events.

then maybe AD? ADA4004, OP467


Thanks! I had looked at the ADA4004 before but it was out of stock. Now
Digikey has 20 in SO, not enough but AD says they'll have more this
month. The OP467 is 6nV/rtHz but that might be ok here, have to run the
numbers one more time. Interestingly, AD had not suggested either as an
alternative. Eight bucks street price, ouch. Oh well, in this case it
might work.

Otherwise just thow together some discretes, because those mentioned are
above 80c.


Believe it or not but this time it's all about performance. Well,
almost. But you are right, these kinds of chips are usually outside my
league from a cost point of view.
 
W

Winfield Hill

Jan 1, 1970
0
Joerg said:
The OPA series seems hard to buy these days and I've heard rumors
of some difficulties. So, I am looking for non-OPA varieties:

<5nV/rtHz would be nice. +/-15V supplies. No back-to-back diodes on the
inputs like the AD8674 has, need to use some of them as comparators and
trackers. Can't easily buffer and they must track some high-Z nodes. I
don't need the full VEE to VDD swing but at least 5V differential or so.

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.
 
P

Phil Allison

Jan 1, 1970
0
"Joerg"
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 :)



** The Natsemi LM833 is dual, low noise ( 4.5 nV), no diodes.

Bout 40 cents each.





........ Phil
 
C

colin

Jan 1, 1970
0
Joerg said:
The OPA series seems hard to buy these days and I've heard rumors of some
difficulties. So, I am looking for non-OPA varieties:

<5nV/rtHz would be nice. +/-15V supplies. No back-to-back diodes on the
inputs like the AD8674 has, need to use some of them as comparators and
trackers. Can't easily buffer and they must track some high-Z nodes. I
don't need the full VEE to VDD swing but at least 5V differential or so.

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 =^.^=
 
J

Joerg

Jan 1, 1970
0
Winfield said:
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.

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 :)
 
R

Robert Latest

Jan 1, 1970
0
["Followup-To:" header set to sci.electronics.design.]
Joerg said:
Thanks! I had looked at the ADA4004 before but it was out of stock.

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
 
R

Rene Tschaggelar

Jan 1, 1970
0
Joerg said:
The OPA series seems hard to buy these days and I've heard rumors of
some difficulties. So, I am looking for non-OPA varieties:

<5nV/rtHz would be nice. +/-15V supplies. No back-to-back diodes on the
inputs like the AD8674 has, need to use some of them as comparators and
trackers. Can't easily buffer and they must track some high-Z nodes. I
don't need the full VEE to VDD swing but at least 5V differential or so.

Joerg,
together with the noise you have to specify the
bandwidth. Most very low noise opamps have
extensive bandwidths, actually all opamps I
remember with GBWs from a few 100MHz are
specified as very low noise with figures in the
range of 3nV/rtHz and below

Rene
 
J

Joerg

Jan 1, 1970
0
Robert said:
["Followup-To:" header set to sci.electronics.design.]
Joerg wrote:

Thanks! I had looked at the ADA4004 before but it was out of stock.


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).

That makes me cringe as well. For lots of dynamic range it's hard to
live with 5V or so. What good does a really low-noise performance do
when the top of the dynamic range is chopped off?
 
J

Joerg

Jan 1, 1970
0
Phil said:
"Joerg"






** The Natsemi LM833 is dual, low noise ( 4.5 nV), no diodes.

Bout 40 cents each.

Neat! Thanks. Comes only in duals but heck, can't beat that price. And
it is 2nd sourced, found it also at ST and ON-Semi. This one ought to be
really popular with high end audio guys yet for some reason I have never
heard them talk about it.
 
J

Joerg

Jan 1, 1970
0
Rene said:
Joerg,
together with the noise you have to specify the
bandwidth. Most very low noise opamps have
extensive bandwidths, actually all opamps I
remember with GBWs from a few 100MHz are
specified as very low noise with figures in the
range of 3nV/rtHz and below

It's below audio in this case. High GBW would not be a problem but the
few that are in the +/-15V range such as some THS devices cannot
tolerate much differential input.
 
J

Joerg

Jan 1, 1970
0
colin said:
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.

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

Robert Latest

Jan 1, 1970
0
["Followup-To:" header set to sci.electronics.design.]
Joerg said:
Neat! Thanks. Comes only in duals but heck, can't beat that price. And
it is 2nd sourced, found it also at ST and ON-Semi. This one ought to be
really popular with high end audio guys yet for some reason I have never
heard them talk about it.

It's just too cheap.

robert
 
F

Fred Bartoli

Jan 1, 1970
0
Joerg a écrit :
It's below audio in this case. High GBW would not be a problem but the
few that are in the +/-15V range such as some THS devices cannot
tolerate much differential input.

Plus those high GBW opamps generally are low noise at high frequency and
have a pretty high 1/F corner frequency. Even bipolar opamps.
 
E

Eeyore

Jan 1, 1970
0
Joerg said:
Robert said:
["Followup-To:" header set to sci.electronics.design.]
Joerg said:
Thanks! I had looked at the ADA4004 before but it was out of stock.

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).

That makes me cringe as well. For lots of dynamic range it's hard to
live with 5V or so. What good does a really low-noise performance do
when the top of the dynamic range is chopped off?

They don't make designers any more like they used to in the old days !

Graham
 
E

Eeyore

Jan 1, 1970
0
Joerg said:
Neat! Thanks. Comes only in duals but heck, can't beat that price. And
it is 2nd sourced, found it also at ST and ON-Semi.

I thought its input current might be too high. Maybe not ?

This one ought to be really popular with high end audio guys yet for some
reason I have never heard them talk about it.

Good point. I came across it quite independently by chance when clicking on the
Audio Op-amp link at national.com. I didn't know it was that decent. I'm curious
that National themselves haven't promoted it more before. Of course it's been
overtaken by more exotic stuff since. The NJM4580 for example is also
inexpensive.

Graham
 
J

Joerg

Jan 1, 1970
0
Eeyore said:
Joerg wrote:




I thought its input current might be too high. Maybe not ?

Yeah, 1uA is a bit highish and so is the offset. Then again, at that
price I am not complaining. We'll have four in a row and the first two
can be calibrated out.
Good point. I came across it quite independently by chance when clicking on the
Audio Op-amp link at national.com. I didn't know it was that decent. I'm curious
that National themselves haven't promoted it more before. Of course it's been
overtaken by more exotic stuff since. The NJM4580 for example is also
inexpensive.

Digikey calls one of the NJM4580 versions "noiseless". Now that's a bit
brazen but the main problem is the stock situation. Zilch.

It's also quite high in input current, at 0.5uA. Says differential
+/-30V and then (note). But I couldn't see any note other than the usual
disclaimer.

BTW, why did they call themselves "New" Japan Radio Corporation? I
already liked the old one, got some of their gear here in the lab.
 
W

Werty

Jan 1, 1970
0
2 kinds of Op Amps ,

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 ..
 
J

Joerg

Jan 1, 1970
0
Eeyore said:
Joerg wrote:

Robert Latest wrote:

["Followup-To:" header set to sci.electronics.design.]
Joerg wrote:


Thanks! I had looked at the ADA4004 before but it was out of stock.

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).

That makes me cringe as well. For lots of dynamic range it's hard to
live with 5V or so. What good does a really low-noise performance do
when the top of the dynamic range is chopped off?


They don't make designers any more like they used to in the old days !

Tell me about it. I am still in disbelief about the percentage of fresh
grads who can't even understand the function of a circuit from a schematic.
 
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