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Old 2nd November 2001, 06:02 AM   #11
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Join Date: Oct 2001
Location: Alvesta, Sweden
Regarding the I/V converter you could try a simple resistor.
I'm sure it will be better than your OPA134.
With careful selection of components in your 12 dB Bessel filter it can be driven directly by a resistor loaded DAC.
You will have less output but that can be fixed in the output stage. I use BurrBrown PCM63 which can accept 0,4 volts before the protecting diodes starts to conduct.
I don't know how AD1862 is built, so I can't say how much voltage you can get from them with a resistor I/V-convertor.

Have you looked at the ADSL OP-amps from Analog Devices ?
Less open loop gain and a open loop -3dB point above 100KHz.
Might be a competitor to LM7171 in your circuit.

Thought more about your feedback ideas, but by intuition the global feedback solution gives me less shrills.
But since it is so easy try both, please do.

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Old 2nd November 2001, 03:02 PM   #12
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Join Date: Jan 2001
Location: Ruhrgebiet
Yes, this is indeed a very interesting solution.
The AD1862 datasheet doesn't say anything anout its max output voltage, current rails for full scale digital are 1 mA. So I will do some measurements and calculations for the high impedance-driven filter. Very good idea, thx a lot!

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Old 3rd November 2001, 08:56 AM   #13
ppl is offline ppl  United States
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Location: Seattle, WA U.S.A.
I have Tried every Combonation of Opamp Buffer one can try and what works best from my point of view is the Multiloop feedback technique as discribed by walt jung in the December 1998 EDN Walts Tools and Tips. http://www.penton.com/ This satisfies the Stability as well as suppling a constant amount of feedback over the Aduio bandwidth. Regarding the BUF-634 This is an Open Loop Device not a Closed Loop one and IMHO sounds Less than Ideal when operated outside the Loop in Addition to having about 35 Mv of DC Offset that the Feedback loop would normaly Correct.
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Old 3rd November 2001, 09:13 AM   #14
ppl is offline ppl  United States
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Hear is a link direct to the Walt Jung artical it is for Dec 14,1998 but also see Dec1 1998 http://www.planetee.com/planetee/ser...ArticleID=1518
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