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Old 9th March 2013, 02:11 PM   #1
Stee is offline Stee  Italy
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Default Power Buffer with Jfet IN and CFP OUT

This universal buffer
works with a bootstrapped source follower
and a power stage CFP controlled by Wilson mirror
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Old 9th March 2013, 03:07 PM   #2
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A fixed bias cascode is not a bootstrap.
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Old 9th March 2013, 03:08 PM   #3
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It reduces the input capacitance and gives some power supply rejection though.
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Old 9th March 2013, 04:39 PM   #4
Stee is offline Stee  Italy
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how you call this function?
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Old 9th March 2013, 05:18 PM   #5
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Fixed bias cascode, no more no less.
If you would connect the 10kOhm of the cascode before the 22 ohm resistors that whould be a bootstrap. I would use Leds though supplied with CCSs because then the Fet drives a high impedance. Just connecting the fixed bias cascode before the 22 Ohm resistors put a burden on the Fets.
Anyway, your circuit has potential but can be improved.
Why the current mirror ? It makes the current in the emitter folower the same then the current in the collector follower. Maybe it would be better to run the collector followers on higher current then the emitter followers. That could be done with a scaled current mirror.
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Old 9th March 2013, 05:52 PM   #6
Stee is offline Stee  Italy
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OK it's better connect the cascode as bootstrap,
a scaled current mirror? intresting!
can you edit the original schematic with your improvement?
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Old 9th March 2013, 05:59 PM   #7
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Later but i do it.
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Old 9th March 2013, 06:02 PM   #8
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The scaling can be done by putting resistors in the emitter feed of your Wilson.
For example a 100 Ohm on the left side and a 50 ohm on the right side.
Then the collector follower runs on double the current then the emitter follower of the Szikley pair.
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Old 9th March 2013, 06:05 PM   #9
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You could also insert a resistor in the collector feed of the emitter followers.
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Old 9th March 2013, 07:42 PM   #10
Stee is offline Stee  Italy
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Default very good evolution

see if the schematic is like your idea
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