[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik, Kaashoek)

[glen english LIST]

generally the ceramic 'soft-termination' types are quiet. steer clear of 
really Hi-k types like Y5V and Z5U.

anything other than CoG and NP0 are going to be like varactors, but that 
wont matter so much IF you choose a nice high voltage. X7R are ok, 
X5R....for PLLs if you choose something with heaps of voltage headroom.

If NPO gets too big, then I use solid tantalum capacitors in slow  PLLs, 
(as the plastic MKT just get too big for my applications)....  but give 
them heaps of voltage headroom - at least 3 x what the use voltage will 
be....... they get much (current) noisier the higher the voltage on 
them..  noise is in 10s of pA/root Hz. varies in mfr....

my 2c.


On 14/07/2022 9:16 am, Richard Karlquist via time-nuts wrote:
> More excellent comments from Bob, this time about microphonic
> capacitors.
>
> It is interesting to note that the LT3042/LT3045 data sheets
>
> recommend a Murata GJ831CR61E106KE83L ceramic capacitor because it is:
>
> 1.  Low microphonic
>
> and
>
> 2.  Has a relatively small loss of capacitance due to DC voltage being
> applied
>
> The amount of capacitance needed is prohibitively high to consider NPO.
>
> This part is listed as "Not Recommended for New Design" at Digikey, but
>
> they have over 24,000 in stock.  See URL:
>
> https://www.eetimes.com/murata-low-profile-capacitors-reduce-acoustic-noise/#:~:text=Murata's%20GJ8%20series%20of%20multi,consumer%20and%20industrial%20electronics%20applications.
>
>
> I see that on the Eval PCB's they use Samsung CL31A106MBHNNNE.  Digikey
> has over 1 million of these in stock.
>
> No info about how good they are.
>
> --
>
> Rick Karlquist
> N6RK
>
> On 2022-07-12 09:17, Bob kb8tq via time-nuts wrote:
>
>> Hi
>>
>> If you have any ceramic capacitors in the mix, they are often microphonic.
>> The X7R versions are typically the best "high C" types. NPO's normally are
>> completely non-microphonic. Other non-ceramic caps should be ok, but
>> who knows.
>>
>> Roughly speaking, 1 nV / Hz should be low enough to not matter. Since all
>> these specs are "typical" one never knows quite what this or that part may
>> be doing. You *should* see a drop putting in a 1 nV in place of a 5 nV.
>>
>> Bob
>>
>>> On Jul 12, 2022, at 7:53 AM, Erik Kaashoek <erik at kaashoek.com> wrote:
>>>
>>> I'm struggling with the noise floor.
>>> First tests where done with a 5nV/sqrt(Hz) opamp. Noise floor with shorted mixer output at 10kHz was -140dBc/Hz. Then I tried with 1nV/sqrt(Hz) opamp, but that made no difference, noise floor at 10kHz was still -140dBc/Hz
>>> The setup was simplified to this schematic: http://athome.kaashoek.com/time-nuts/PNA/SSPNA.JPG
>>> The REF_buffer creates a virtual ground, the Audio_LNA amplifies into the differential audio output .
>>> Why did the lower noise opamp not make a difference?
>>> Also the setup is acting like a nice microphone. Tapping the housing is clearly audible. Which component may be causing the microphony?
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-- 
Glen English
RF Communications and Electronics Engineer

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