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Old 8th February 2013, 11:54 AM   #821
smms73 is offline smms73  Portugal
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Quote:
Originally Posted by keantoken View Post
. R13/C2 looks potentially problematic and may make it prone to oscillation with inductive source impedance. This can usually be fixed with an input shorting cap, but point is to be aware of the issue so that you know what is going wrong and why in case of problems.
The bootstrapped cascodes creates a loop that is prone to oscillate at rf , R13/c2 is for adding loss at high frequencies, normally I have good results with this, in theory the c2 should be connected to positive rail, but in that way the PSRR at high frequency get worse.

I have see a lot of bootstapped cascode designs without any means to stop this oscillations to occur . But that is not much advised.
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Old 8th February 2013, 12:05 PM   #822
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Originally Posted by keantoken View Post
I ordered a bunch of ferrite beads a while back which have been sitting in a bin. These can be quite helpful. I wish I had tried them out sooner. They're easy to test on a prototype and instantly reusable. Like any reactive component, you have to know how to use them, but they can make you work less for the same result
Ferrite beads are non linear inductors ( hysteresis curve of ferrite ), some discourage the use of ferrite beads in audio circuits ,what is your experience with them , do they increase distortion?
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Old 8th February 2013, 12:39 PM   #823
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Speaking of parasitic inductances and Just for curiosity , the most problematic situation that i enconter was with eGaN FETs , this type of FETs dont even have leads and have several souces and drain connections in parallel to lower to the extreme the parasitic inductance, at the speed they can switch the slightest inductance can cause ringing with enought voltage to damage them , especially in the gate that have maximum gate source voltage of 6 volts.

simulation with pcb traces parasitic inductances , in power switching is a must.

this is the link for the fets that i was talking (they are the future):

EPC2001
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Old 8th February 2013, 12:54 PM   #824
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I End for now, with this citation that seems appropriate, and sadly very true.

"Every Amplifier is Waiting to Oscillate and Every Oscillator is Waiting to Amplify"
by Bonnie C. Baker

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Old 8th February 2013, 02:02 PM   #825
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just for show how even a 0.5nH (a to220 lead has 12 nH of inductance) can have impact, i post this circuit the first without the drain parasitic inductance (500pH) the second with the added parasitic inductances, this is a extreme example and i just post it here for curiosity, in non swithing audio aplications this is not that bad .

with 2nH of parasitic the switch node reach 75 volts because of riging.
simulating this circuit without the pcb trace parasitic inductances can have drastic consequencies.
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File Type: png epc1001_inductance.png (290.1 KB, 642 views)
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Old 8th February 2013, 10:52 PM   #826
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I'll use my current prototype as an example. I have an error correction buffer going to a simple IRF250 power buffer. The buffer is an advanced circuit of mine, the power buffer is just a source-follower biased at 500mA with a 10R resistor (driving 8" FR's). Without using ferrite beads, I might dicker around endlessly with the circuit, trying different compensations, RC snubbers, even regressing the design just to stop parasitic oscillations and reactivity that result in sibilance and fatigue. Maybe because I am using a 10R gate stopper for the IRF250, since I don't like the sound of a large gate stopper. But if I use ferrite beads, I can simply add one or two in series with the output of the line buffer, and this is pretty effective for eliminating sibilance in this application without losing the image depth and clarity that is so hard to achieve. Maybe not quite the same circuit, but it's worth a try.
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Old 12th April 2013, 02:42 PM   #827
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Hey Sergio, any news on your lovely circuit?
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Old 10th October 2013, 08:35 PM   #828
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Originally Posted by Shinja View Post
I know this is a bit late, but what is the benefit of this? All the noise from the psu will be injected in the signal, not?
So why is it so clever?

For some reason I cannot quote a pic, I'm referring to this post:
dac I/V convertion with very low distortion
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Old 11th October 2013, 01:53 PM   #829
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The supply could be a battery now that I think about it....

But, still, how on earth does the opamp work?!
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Old 11th October 2013, 07:30 PM   #830
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Originally Posted by Odysseas View Post
The supply could be a battery now that I think about it....

But, still, how on earth does the opamp work?!
That is a circuit that uses floating power supplies , first I think you should check this thread to grasp the concept, then if you still need I will explain the rest. Dont forget that the current that is injected to the circuit by the I1 will have to return to ground and the only path is by the output resistor.

Zen -> Cen -> Sen, evolution of a minimalistic IV Converter
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