Why is the shunt regulator push-pull? Because of the series regulator first and the shunt regulator then? On Tue, Nov 22, 2011 at 8:59 PM, <[email protected]> wrote:
> If you want low noise voltage regulation, use a shunt regulator. If the > load is low current, feed it with a floating current source such as a > depletion mode jfet (or several in parallel). These are also sold as > current regulating diodes. > > I've used this scheme in IC designs. You also find it in high end audio > design. > > The shunt design is push pull. If the shunt is designed well, the ultimate > high frequency feed through from the power supply, assuming ideal caps, is > simply a capacitor divider based on the bypass cap and the capacitance > across the current source. > > The bozos at Broadcom have actually patented using shunt regulation in > their chips. Good luck enforcing that patent. > > -----Original Message----- > From: [email protected] > Sender: [email protected] > Date: Tue, 22 Nov 2011 14:18:20 > To: <[email protected]> > Reply-To: Discussion of precise time and frequency measurement > <[email protected]> > Subject: Re: [time-nuts] Low noise power supplies for time nuts circuitry > > As Bob Pease used to say: Spice plots are good for padding bird cages, not > much else :) > > Hittite has a fantastic new ultra low noise LDO for VCO's. Haven't had a > chance to check that out, but it looks very promising. Has anyone tried > that > part here? > > Also, remember that those caps are microphonic most of the time, and could > actually worsen supply noise in the presence of vibration. > > I get noise floors of below -170dBc with just simple RC or LC filtering on > the power supplies, say 10 Ohms into 100uF Tantalum in parallel with some > 10nF to 100nF ceramics (or better Polyester caps), all following the > typical > Linear Technologies low noise LDO's. That will cut off at 160Hz already, > and go down at 40dB per decade if two filters are cascaded. Use two 100uF > Tantalums or 22Ohms resistors for a <80Hz cut-off. > > At close-in frequencies, the crystal will likely be the worst noise source > and overpower the supply noise by far. It's hard to get better than -108dBc > at 1Hz, and -138dBc at 10Hz at 10MHz anyhow. > > For high frequency switcher noise, use shielded (TDK etc) 33uH inductors in > series to a 10 Ohm resistor, into 100uF Tantalums with 10nF and 220pF in > paralell. Cuts off <160Hz and has very good isolation at high frequencies > without radiating. > > For the best performance against supply noise, simply use differential > techniques. > > bye, > Said > > > In a message dated 11/22/2011 10:52:29 Pacific Standard Time, > [email protected] writes: > > In message <[email protected]>, > Ulrich Ban > gert writes: > > >It seems to turn out as if the well known Wenzel suggestions for voltage > >regulator finesse were not state of the art [...] > > > I've played a bit with the Wenzel circuits and they can provide truly > outstanding damping, my best was 80dB using a HP VHF transister I can't > remember the number of. > > And yes, they are very sensitive to just about everything, in particular > temperature. > > But getting at good solid 30+dB damping is not _that_ hard, in particular > for very low-current constant loads, such as X-tal oscillators. > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > [email protected] | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by > incompetence. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
