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barrows 7th July 2012 10:57 PM

"Best" local oscillator regulator?
I have not seen this specifically discussed before, so I was looking for some expert opinions and recommendations. It has come to my attention, that perhaps, high feedback regulators may not be the best choice as the final regulation stage for an oscillator module. Right now I am using Twisted Pear Audio Tridents to power the two oscillators (CCHD-957s) on my async USB interface.
Any ideas on powering clocks, and any available oscillators or simple oscillator circuits to try (non feedback perhaps...)

DUG 7th July 2012 11:50 PM

Well, the oscillators wants 3.3V +- 0.3V so they appear not to be too fussy about their supply.

The Trident looks like 3.3V +- 1% 100mA max with max input of 5.5V

Depending on accuracy and package, I did a search of Digikey and found 387 instock that might be accurate enough for the job. (I would have narrowed it down further but the accuracy column seems to have disappeared and I don't know what package you would like to use.)

I've used MIC5201-3.3YS TR and it seems to work fine. It is an SOT-223 package and I like the pin-out because it is similar to the LM78xx TO-220 types in that the tab is GND and I ground it to the ground plane as a heat sink.

barrows 8th July 2012 01:24 AM

potential problems...
Oscillator modules are very, very sensitive to any supply noise, and jitter levels are highly dependent on having a super clean DC supply. Additionally, regulator output impedance may be very important to keep the clock frequency from traveling back through the supply and contaminating the other supplies in the DAC.

So noise, and output impedance are two critical factors, whereas voltage stability may not be such a critical factor.

qusp 8th July 2012 02:48 AM

use a battery, simple. they want low noise, they are about as benign (not dynamic at all, not high current at all) a load as you'll get. stability is important, just not very hard to achieve

qusp 8th July 2012 02:53 AM

alternatively Demian (1audio) has presented some very nice discrete clock regs, including ground isolated output. you can search, or just pm me your email addy that would be easier for me than searching for you

marce 8th July 2012 08:32 AM

LDO regulator circuit for your clock, used extensively these days on high rel designs, plenty to choose from from Linear or Texas. Layout and if possible simulation of layout will get the best results with clocks, and minimum distance for clock signal to travel.

qusp 8th July 2012 08:44 AM

the dac clock used to have an LT LDO as standard in this design but they changed to shunts. hes trying to move away from massive feedback and I presume something better than an LDO. non feedback clock circuits are going to be pretty shithouse IMO, not even sure how you would do it in any meaningful way. I guess this is Loriens board yes barrows?

barrows 8th July 2012 01:55 PM

Thanks Qusp. I have used batteries (LiFePO) before, and did not like the charging hassle, but for just oscillators it might be worth another try. Are you having good results with LiFePOs nominal 3.2 volts direct to an 3.3V oscillator with no further circuitry? I guess the LiFePO output voltage is stable enough for this application.
Has anyone actually measured the LiFePO battery for noise? I know there is noise caused by the internal chemical reactions, but have never seen a measured spec?
I am using an SOtM async USB receiver board so the layout is what it is-I am just adding separate power supply for the clocks with a dedicated regulator for each of them, and am definiterly looking for something better than IC regs. I hoped to draw out the experts who might be able to discuss the feedback question for clock regulators.
I will also search for Demian's designs, as I would like to read the context of the threads they came up in as well.

marce 8th July 2012 02:13 PM
some figures on this thread regarding battery noise.

qusp 8th July 2012 02:30 PM

just quickly, i'll reply to the rest later, but Demian presents his regs earlyish in the fifo thread and there is also some talk of it in the widget thread, as they are included on the PCB as an option. I still havent seen proper testing of lifepo4 noise either, but under such low current draw I really doubt its even worth worrying about, plus the benefits of being totally floating.

i'm just not sure how you would make a non feedback clock at a specific audio related frequency, the output stage of the clocks buffers but also sets the speed by multiplication/division. without feedback you would be stuck with the fundamental frequency of the crystal and they simply dont oscillate at audio frequencies.

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