Cirrus Logic amplifiers

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?

Hot damn! Thanks.

Must be a chopper. 50 pF Cin!

John

Right, at 0.0000001 Hz, etc.

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 Thanks,
    - Win

LOL!

Thanks! :-D Rich

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

Best regards, Spehro Pefhany

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

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

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

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|  James E.Thompson, P.E.                           |    mens     |
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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

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.

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 Thanks,
    - Win

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

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 Thanks,
    - Win

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:

and the current one:

getting more technical:

"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..."

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

Thanks. Will try to find a copy.

Robert

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

John