[time-nuts] xtal oscillator phase noise

[Mike Feher]

The emitter follower should have a very low output impedance, so, I would
not be too concerned about it's driving capabilities. If you must have 50
ohms, well, then just connect a 47 ohm resistor after the 1 nf capacitor and
measure it there, without U1. The confusing thing about the ADR455 is that
above, on the schematic, you claimed you derived the 12V from the ADR455. I
am not familiar with it, but, in that case, how did you get the 12 V from
the 5 volt reference? - Mike

 
 
Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960
 
 

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Henk ten Pierick
Sent: Tuesday, January 01, 2008 8:03 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] xtal oscillator phase noise

On Jan 1, 2008, at 13:42, Mike Feher wrote:

> Henk -
>
> Did you try to measure the PN out of the oscillator directly  
> without the
> buffer amp (U1)?

No, but I will do it. I have to find a way, the emitter follower is  
not expected to drive 50 ohm.

> Also, what is the voltage from V1? Is it also 12V?

The ADR455 is a 5volt reference.

> HNY -

Same to you all.

Henk

> Mike
>
>
>
> Mike B. Feher, N4FS
> 89 Arnold Blvd.
> Howell, NJ, 07731
> 732-886-5960
>
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts- 
> bounces at febo.com] On
> Behalf Of Henk ten Pierick
> Sent: Tuesday, January 01, 2008 7:25 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] xtal oscillator phase noise
>
>
> On Dec 30, 2007, at 3:42, Bruce Griffiths wrote:
>
>> Henk
>>
>> The 30dB/decade phase noise slope could be the result of the  
>> effect of
>> low pass filtering a power supply or reference source that has
>> significant flicker noise.
>
> The reference used is an ADR455. I have not seen references
> significant better. Suggestions?
>
>> Lack of local RF feedback and /or high dc gain from base to
>> collector in
>> BJT buffer stages can produce significant flicker phase noise.
>
> I have now doubled the dc voltage for the oscillating transistor for
> the reduction of junction capacitances. It had no result on phase  
> noise.
>
> Is low hfe better for phase noise?
>
> Henk
>
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