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I/V stage for ES9028Q2M
I/V stage for ES9028Q2M
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Old 8th February 2018, 05:36 AM   #11
gandolf is offline gandolf  United States
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Quote:
Originally Posted by DPH View Post
Gandolf, go look for something like the 9018 or 9016 Datasheet online, the spec design is essentially a LME49720 configured as I/V's, pretty much classic design.

Also, the parts you're suggesting aren't low noise at audio bandwidth, maybe something like the OPA1632, but feel free to simply use a dual opamp instead.

It's also not difficult to make a center-tap reference from a precision resistor divider and a capacitor (for stability). If you look for JensH's posts in one of the 9038q2m threads, he's got a circuit. Scott Wurcer threw in a nice general form (and some things to think about) for an I/V in the AD797 http://www.analog.com/media/en/techn...eets/AD797.pdf pg 17.

There's a bevy of ways to do this. A quick/but not ridiculously quick low-noise general purpose opamp would be excellent. If you want to go nuts, look at an OPA1612 or better ADA4898. Mind your layout though.
Thanks for the information. I do understand AD8138 is kind of noisy, but even LT1819 is not quiet enough? OPA1612's spec is indeed very impressive, but the high supply voltage requirement and the cost are holding me back. OPA1632 does not have the unity gain stable feature that I am also looking for. What about OPA1662? Its noise performance is kind of in between, I am not sure if its 17V/us slew rate is too slow.

By the way, I was trying to search for the posts by JensH but couldn't find it. Would you mind post it here? Thank you very much.
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Old 8th February 2018, 05:54 AM   #12
DPH is offline DPH  United States
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Chinese ES9018K2M I2S DAC

And the posts nearby will give you something to chew on.

LT1819 comes in a funky package--make sure you can solder it. Cannot see what it brings to the table that couldn't better be solved by slower precision opamp (cough, LME49720?). There's absolutely no need for 400 MHz bandwidth, and you're sacrificing elsewhere to get it. What sort of output are you looking for? You can readily run these guys down towards their minimum voltage, although some of their performance may be (marginally) compromised. Also, I'd think even the more conservative members would consider a 200 kHz power bandwidth (back out your slew rate) a sufficient overprovisioning.
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Old 8th February 2018, 06:17 AM   #13
chris719 is offline chris719  United States
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I/V stage for ES9028Q2M
Quote:
Originally Posted by gandolf View Post
Thanks for the information. I do understand AD8138 is kind of noisy, but even LT1819 is not quiet enough? OPA1612's spec is indeed very impressive, but the high supply voltage requirement and the cost are holding me back. OPA1632 does not have the unity gain stable feature that I am also looking for. What about OPA1662? Its noise performance is kind of in between, I am not sure if its 17V/us slew rate is too slow.

By the way, I was trying to search for the posts by JensH but couldn't find it. Would you mind post it here? Thank you very much.
Check out ADA4896/ADA4897 if you are still hung up on bandwidth. It can't handle more than 10V on the supply but since you want to run 3.3 it should be fine.

LT1819 is still noisier than the best choices. It's even noisier than good JFET input amps like OPA1642 and OPA827.

Also, I didn't look too closely at those pics you posted, but make sure you are using resistor values that the op-amp can actually drive.
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Old 8th February 2018, 06:43 AM   #14
gandolf is offline gandolf  United States
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Quote:
Originally Posted by DPH View Post
Chinese ES9018K2M I2S DAC

And the posts nearby will give you something to chew on.

LT1819 comes in a funky package--make sure you can solder it. Cannot see what it brings to the table that couldn't better be solved by slower precision opamp (cough, LME49720?). There's absolutely no need for 400 MHz bandwidth, and you're sacrificing elsewhere to get it. What sort of output are you looking for? You can readily run these guys down towards their minimum voltage, although some of their performance may be (marginally) compromised. Also, I'd think even the more conservative members would consider a 200 kHz power bandwidth (back out your slew rate) a sufficient overprovisioning.
Ok, I see your point. Soldering wise there is no problem... I have a small Chinese made reflow oven, successfully soldered QFN before. The reason why I am in favor of LT1819 is that it is very stable, 90-degree phase margin all the way. LME49720 and OPA1612 requires > 5V supply so they are out of question. OPA1662 works with 3.3V, but its phase margin is merely 58 degree, makes me nervous. chris719 suggests ADA4896, it seems like a good candidate. Man, they are EXPENSIVE.
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Old 8th February 2018, 06:55 AM   #15
gandolf is offline gandolf  United States
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Originally Posted by chris719 View Post
Check out ADA4896/ADA4897 if you are still hung up on bandwidth. It can't handle more than 10V on the supply but since you want to run 3.3 it should be fine.

LT1819 is still noisier than the best choices. It's even noisier than good JFET input amps like OPA1642 and OPA827.

Also, I didn't look too closely at those pics you posted, but make sure you are using resistor values that the op-amp can actually drive.
Yeap ADA4896 looks very promising.

Simulation setup:
Click the image to open in full size.

Transfer function:
Click the image to open in full size.

Transient with 7mAp-p @10KHz:
Click the image to open in full size.
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Old 8th February 2018, 06:57 AM   #16
Keruskerfuerst is offline Keruskerfuerst  Germany
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Try to remove R2 and set C1 to some 100 pF.
Can you give the output impedance of the DAC?

Last edited by Keruskerfuerst; 8th February 2018 at 07:01 AM.
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Old 8th February 2018, 07:32 AM   #17
gandolf is offline gandolf  United States
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Originally Posted by Keruskerfuerst View Post
Try to remove R2 and set C1 to some 100 pF.
Can you give the output impedance of the DAC?
No, it does not work, phase margin becomes negative. R2 is needed to limit the feed-forward current from input to output at high frequency. Otherwise, the RHP zero will severely degrade the phase margin.

I am sorry, the details of the DAC is protected by the NDA.
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Old 8th February 2018, 08:32 AM   #18
Keruskerfuerst is offline Keruskerfuerst  Germany
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If no details of the DAC are availaible to the engineers, then it is impossible to construct a I/V stage and post filter.

Last edited by Keruskerfuerst; 8th February 2018 at 08:47 AM.
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Old 8th February 2018, 06:15 PM   #19
Keruskerfuerst is offline Keruskerfuerst  Germany
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Is the DAC a multi or 1 bit DAC?
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Old 8th February 2018, 06:41 PM   #20
gandolf is offline gandolf  United States
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Originally Posted by Keruskerfuerst View Post
Is the DAC a multi or 1 bit DAC?
It is ES9028Q2M from ESS, a Delta/sigma DAC, I believe this is what you are referring as '1-bit' DAC?
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