More bad info.
anyway ---
What specs are important to audio? Do we really care about many of the DC precision/specs that much? The VFA excels more easily in some areas.... but those areas have no benefit to audio.
THx-RNMarsh
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For one thing lots missing on the second one like the current in Q7 and Q8 is undefined as shown, the complete circuit is much more complicated. That said to the customer the basic functionality with respect to what the feedback network does is the same.
The second circuit probably has far superior distortion performance at higher frequencies due to the added gain stage, but probably does not drive as much Cload. The R/C circuit in the first schematic transfers the load to the gain node at high frequencies and can be a distortion maker. There are designers that think all op-amps should drive 1000pF hanging directly on the output.
50 pf/foot for 10-20 feet seems reasonable for IC amp to be able to drive that much C in an audio system without increasing distortion or becoming unstable. 500-1000pfd.
THx-RNMarsh
THx-RNMarsh
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Basically yes (they do have different part numbers) and you have discovered what is wrong with op-amp rolling.😉
50 or even 100 is OK.....sometimes. Higher would be a problem though. It increases the susceptibility to pick up noise on the lines being driven. and it can affect input stage balance and noise following.
THx-RNMarsh
THx-RNMarsh
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Please humor me Scott, I am intrigued:
"A very large customer asked me to convert one of our CFA DSL drivers to VFA and with the same internal degeneration as Rf and tweak of the compensation"
You mean some customers spec their requirements to that tech detail? Or do I miss something?
Jan
"A very large customer asked me to convert one of our CFA DSL drivers to VFA and with the same internal degeneration as Rf and tweak of the compensation"
You mean some customers spec their requirements to that tech detail? Or do I miss something?
Jan
Current output and current feedback are two different things in my mind
as is
Voltage output and voltage feedback
mix 'n match as required:-
Current output amplifier using voltage feedback
Voltage output amplifier using current feedback
This whole semantic thing is being put up like a windmill so the Don Quixotes' can have a run at something.
What's the point? How's that old saying go 'if it smells like a skunk, it probably is a skunk'
They do sometimes, but in this case they simply wanted freedom of choice in the impedance level of the external circuit.
I have been to many large customers where I got a lecture in solid state physics and the customer wanted x and y. I always had a PhD in tow. They could explain to the customer what was and was not possible. Most of the customer product designers never understood the workings in a fab and why we would not do certain things. But they were often pretty good at digging into the product spec detail and were ok on the device theory side.
I thinking specifically of customers in Germany and in the USA - Auto, telecoms and computing - all power stuff.
If it made business sense, I would go and get the funding for it. If it didn't work out business wise, I got hammered for it. 😀
I would think that as a customer I should specify what it should do, not how it should do it.
Like Bruno's adage: 'The road to hell: specify the design and accept the performance; the road to heaven: specify the performance and accept the design'.
But you can probably tell I have zero experience in this field. 😡
Jan
Like Bruno's adage: 'The road to hell: specify the design and accept the performance; the road to heaven: specify the performance and accept the design'.
But you can probably tell I have zero experience in this field. 😡
Jan
Not so much telling us how to do it, but not understanding why what they wanted was not financially viable. 🙂
All posts by a previously banned member and subsequent correspondences thereof have been deleted as collateral.
Yes. We used to call it portfolio pruning. Not profitable, or worse than planned yields or we moved the fab and did not want low volume stragglers in there.
But we digress. Back to CFA’s!
At your service Bonzai! ;-)
Michael Steffes, who has been mentioned before in the context of an article on CFA and VFA issues, wrote an interesting article discussing the evolution of opamps and the way CFA and VFA designers are trying to keep their own advantages and obtain the other's ;-)
Planet Analog - Michael Steffes - DC precision considerations for high speed amplifiers . Quite interesting and informative.
Jan
Michael Steffes, who has been mentioned before in the context of an article on CFA and VFA issues, wrote an interesting article discussing the evolution of opamps and the way CFA and VFA designers are trying to keep their own advantages and obtain the other's ;-)
Planet Analog - Michael Steffes - DC precision considerations for high speed amplifiers . Quite interesting and informative.
Jan
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Hello Jan,
This article shows pretty well that as two oil stains the so called VFA and CFA worlds are flowing into each other.
VFA’s designs are more and more making use of CFA know how and vice versa.
At the end we have just all kind of Fantastic Feedback Amps (FFA) and the whole semantic issue will be a thing of the past. 😀
Hans
This article shows pretty well that as two oil stains the so called VFA and CFA worlds are flowing into each other.
VFA’s designs are more and more making use of CFA know how and vice versa.
At the end we have just all kind of Fantastic Feedback Amps (FFA) and the whole semantic issue will be a thing of the past. 😀
Hans