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Cirrus Logic amplifiers

S

Spehro Pefhany

Jan 1, 1970
0
I am trying to get a few CS3001 op amps that have almost unbelievable
low frequency noise voltage. But none of the normal distributors I
deal with carry Cirrus Logic. Can anybody tell me where I can get my
hands on a few of these?

Newark have them in stock.


Best regards,
Spehro Pefhany
 
J

John Popelish

Jan 1, 1970
0
I am trying to get a few CS3001 op amps that have almost unbelievable
low frequency noise voltage. But none of the normal distributors I
deal with carry Cirrus Logic. Can anybody tell me where I can get my
hands on a few of these?
 
S

Spehro Pefhany

Jan 1, 1970
0
The jaw dropper for me was the up to 1000 trillion open loop gain.

Yes, that should pretty much eliminate it from the error budget.


Best regards,
Spehro Pefhany
 
J

John Popelish

Jan 1, 1970
0
John said:
Must be a chopper. 50 pF Cin!

The jaw dropper for me was the up to 1000 trillion open loop gain.
 
W

Winfield Hill

Jan 1, 1970
0
Spehro Pefhany wrote...
Yes, that should pretty much eliminate it from the error budget.

Right, at 0.0000001 Hz, etc.
 
J

John Popelish

Jan 1, 1970
0
Winfield said:
Spehro Pefhany wrote...



Right, at 0.0000001 Hz, etc.

Weirdly, they are stable at a closed loop gain of 10, but not at a
closed loop gain of 10,000.
 
J

John Larkin

Jan 1, 1970
0
Weirdly, they are stable at a closed loop gain of 10, but not at a
closed loop gain of 10,000.

There are a number of weird things about this chip. There are lots of
chopper amps around that have less personality.

John
 
R

Robert

Jan 1, 1970
0
John Larkin said:
There are a number of weird things about this chip. There are lots of
chopper amps around that have less personality.

John

Looked at their web site a bit but couldn't find anything on the "Multipath"
they talk about as a big part of several of their chips including the Amps.
I have a vague recollection from quite a while back (Electronic Design?) of
a "multipath" approach where they split the input frequency range at the
input, each band gets it's own gain path, and then they combine them at the
output. All on chip.

Anybody seen a reference like this?

Robert
 
J

Jim Thompson

Jan 1, 1970
0
Looked at their web site a bit but couldn't find anything on the "Multipath"
they talk about as a big part of several of their chips including the Amps.
I have a vague recollection from quite a while back (Electronic Design?) of
a "multipath" approach where they split the input frequency range at the
input, each band gets it's own gain path, and then they combine them at the
output. All on chip.

Anybody seen a reference like this?

Robert

Are you perhaps thinking of "feed-forward"? Higher frequencies are
fed around the DC-accuracy (limited bandwidth sections), resulting in
a substantial improvement in usable gain-bandwidth product.

...Jim Thompson
 
R

Robert

Jan 1, 1970
0
Jim Thompson said:
Are you perhaps thinking of "feed-forward"? Higher frequencies are
fed around the DC-accuracy (limited bandwidth sections), resulting in
a substantial improvement in usable gain-bandwidth product.

...Jim Thompson

Doesn't sound like what I vaguely remember but I definitely could be
mistaken.

Robert
 
W

Winfield Hill

Jan 1, 1970
0
Robert wrote...
Doesn't sound like what I vaguely remember but I definitely could
be mistaken.

Establishing a feed-forward path is an extremely useful scheme
in opamp circuits, which I first learned from Robert Widlar in
the 60s. He elaborated in app notes for NSC's LM301A opamp,
which he designed. Robert at Yahoo, I can recommend it to you.
 
S

Spehro Pefhany

Jan 1, 1970
0
Doesn't sound like what I vaguely remember but I definitely could be
mistaken.

Robert
Here's a press release on another similar (earlier) Cirrus product:

http://www.cirrus.com/en/press/releases/P26.html

and the current one:
http://www.cirrus.com/en/press/releases/P311.html

getting more technical:
http://www.imec.be/esscirc/ESSCIRC2002/PDFs/C08.04.pdf
"It is targeted towards the applications where the
input signal is low frequency < 1kHz and the signal level
is in mV range and a high THD is required."

There seems to be an IEEE paper here but I don't have a subscription:
"A Five Stage Chopper Stabilized Instrumentation Amplifier..."
http://www.google.com/url?sa=U&star...5639/15113/00688092.pdf?arnumber=688092&e=747


Best regards,
Spehro Pefhany
 
W

Winfield Hill

Jan 1, 1970
0
Spehro Pefhany wrote...
There seems to be an IEEE paper here but I don't have a subscription:
"A Five Stage Chopper Stabilized Instrumentation Amplifier..."

Axel Thomsen, June 1998. "A Five-Stage Chopper-Stabilized Instrumentation
Amplifier Using Feedforward Compensation," Proc, Symposium on VLSI Circuits.
 
J

John Popelish

Jan 1, 1970
0
Spehro said:
Here's a press release on another similar (earlier) Cirrus product:

http://www.cirrus.com/en/press/releases/P26.html

and the current one:
http://www.cirrus.com/en/press/releases/P311.html

getting more technical:
http://www.imec.be/esscirc/ESSCIRC2002/PDFs/C08.04.pdf
"It is targeted towards the applications where the
input signal is low frequency < 1kHz and the signal level
is in mV range and a high THD is required."

The gain and phase curves in this one look very similar to those of
the CS3001.
 
S

Spehro Pefhany

Jan 1, 1970
0
The gain and phase curves in this one look very similar to those of
the CS3001.

One interesting thing to me in the above paper is the icky "small
oscillation" that occurs when the output approaches the supply rails
from either direction. If you were expecting it to saturate
gracefully, this could be a nasty, nasty gotcha (assuming the CS3001
does the same thing, which it may not).

Of course, they don't mention it in the CS3001 datasheet, so surely it
must be okay, right? ;-)


Best regards,
Spehro Pefhany
 
R

Robert

Jan 1, 1970
0
[snip]
Here's a press release on another similar (earlier) Cirrus product:

http://www.cirrus.com/en/press/releases/P26.html

and the current one:
http://www.cirrus.com/en/press/releases/P311.html

getting more technical:
http://www.imec.be/esscirc/ESSCIRC2002/PDFs/C08.04.pdf
"It is targeted towards the applications where the
input signal is low frequency < 1kHz and the signal level
is in mV range and a high THD is required."

There seems to be an IEEE paper here but I don't have a subscription:
"A Five Stage Chopper Stabilized Instrumentation Amplifier..."
http://www.google.com/url?sa=U&star...5639/15113/00688092.pdf?arnumber=688092&e=747


Best regards,
Spehro Pefhany

Thanks. Will try to find a copy.

Robert
 
J

John Larkin

Jan 1, 1970
0
Robert wrote...

Establishing a feed-forward path is an extremely useful scheme
in opamp circuits, which I first learned from Robert Widlar in
the 60s. He elaborated in app notes for NSC's LM301A opamp,
which he designed. Robert at Yahoo, I can recommend it to you.


It was done in the tube days, using a mechanical chopper stage to add
lf gain and dc stability to a tube opamp.

John
 

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