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Just for fun: a superreg with <12 discretes??! ?! ?
Just for fun: a superreg with <12 discretes??! ?! ?
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Old 17th January 2019, 04:36 PM   #11
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by Elvee View Post

Click the image to open in full size.

Unsurprisingly, all of this greatly improves the noise performance: it is now lower than 0.4µV for the 10Hz to 10kHz bandwidth.
I am presently unable to tell how much lower it is: I have reached my measurement limit.

I may be able to give more information in one or two weeks.
I have been able to refine the measurement, now that I have a proper measuring gear: the noise in the 10Hz to 10kHz range is revised to 0.25µV, but this does not represent the ultimate limit: the circuit is still in the breadboard form, and most of the visible noise are bursts from the PLC, pervading everything.
The second contributor is 50Hz/100Hz + harmonics induced from the environment.
"True" noise is thus somewhat lower, probably in the 0.15µV region
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Old 17th July 2019, 02:04 PM   #12
Mark Johnson is offline Mark Johnson  United States
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Just for fun: a superreg with <12 discretes??! ?! ?
The schematic in post #11 confuses me a little bit.
  • Is the base of transistor Q5 actually connected to the regulator output node?
  • Does any current flow in resistor R3? Its two terminals appear to be shorted.
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Old 17th July 2019, 02:24 PM   #13
basreflex is offline basreflex  Spain
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Q5 is a cascode, and the output net is a convenient level for its base.
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Old 17th July 2019, 02:59 PM   #14
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by Mark Johnson View Post
The schematic in post #11 confuses me a little bit.
  • Is the base of transistor Q5 actually connected to the regulator output node?

Yes, it is, for the reason given by Basreflex.
However, it leaves little breathing space for the transistors, and it demands a low Vto from the PMOS to be able to operate in ~LDO mode, which is why I opted for a divider in the practical application I used it for:

Click the image to open in full size.
  • Quote:
  • Does any current flow in resistor R3? Its two terminals appear to be shorted.
It is one of the open-loop enhacement tweaks: when the short is removed, this small resistor (it could be a few mm of track) creates a negative resistance that compensates the residual output impedance.

It can be made larger, to pre-compensate the downstream wiring resistance for example.

R1/C1 forms the open-loop ripple compensator when connected to the emitter of Q5.

All that is explained in the first post
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