[time-nuts] xtal oscillator phase noise

Mike Feher mfeher at eozinc.com
Tue Jan 1 09:47:50 EST 2008


Yes, that is what I figured regarding the 12V. For me, it has more or less
been a rule of thumb, but, I think at 10 MHz the best you could do, due to Q
and transistor noise and gain, was about - 155 dBc/Hz at about 100 Hz from
the carrier. I do not recall from your earlier post what you are actually
measuring. I would think anything close to - 150 dBc/Hz would be very good.
That is of course if you can even measure it at its fundamental frequency. -
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 9:20 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] xtal oscillator phase noise

On Jan 1, 2008, at 14:13, Mike Feher wrote:

> 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.

Yes

> 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

Sorry for the confusion. The 12 volt is derived from the 5 volt  
reference by a simple circuit, the usual series regulator build with  
discrete transistors. It will add some noise to the noise of the ADR455.

> 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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