FreeLists / si-list / [SI-LIST] Re: PLL Loop filter

[Ray Anderson <reanderson@xxxxxxxxxxxxx>]

David Greig wrote:

>Hi Girish
>
>I would hazard a guess that the filter cap is ceramic, and another guess
>that it is surface mounted in a mechanically unsupported area of the board.
>
>Most ceramics exhibit a piezoelectric effect. The value will also alter on
>board deflection, in the order of 0.1% to 0.5% of value in the extreme
>(before popping off!).
>
>Film caps do not have a piezoelectric effect.
>
>
>Best Regards
> 
>David Greig
>  
>
.I concur with David on this. In previous work on satcom synthesizers, 
the inclusion of ceramic capacitors in the loop filter was the kiss of 
death with regards to vibration.

The original poster theorized that the capacitance might be changing 
with vibration. I believe that the piezoelectric voltage generated by 
the ceramic dielectric material is injecting an undesired noise signal 
into the loop which is causing the difficulties.

Note that most ceramic capacitors use (or at least used to) some varient 
of barium titanate as the dielectric material. This is the same material 
that is used to fab sonar transducers because it exhibits piezoelectric 
properties.

-Ray

------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List FAQ wiki page is located at:
                http://si-list.org/wiki/wiki.pl?Si-List_FAQ

List technical documents are available at:
                http://www.si-list.org

List archives are viewable at:     
                http://www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu