The Cyber-Spy.Com Usenet Archive Feeds Directly
From The Open And Publicly Available Newsgroup
This Group And Thousands Of Others Are Available
On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic,
Opinions Or Content Posted To This Or Any Other
Newsgroup. This Web Archive Of The Newsgroup And
Posts Are For Informational Purposes Only.
From: email@example.com (Cheng-Yang Tan)
Subject: Designing crystal filter, any advice?
Date: 18 Jan 2003 00:30:43 GMT
Organization: Fermi National Accelerator Laboratory
NNTP-Posting-Date: 18 Jan 2003 00:30:43 GMT
X-Newsreader: EmTec News for OS/2 [version: 4.6b]
I am currently designing a crystal bandpass filter around 53MHz.
I have found the crystal which is a Citizen CM309 3rd overtone
crystal and am using the AADE filter design software, I started with
the 3rd order linear phase filter an then removed the other two
crystals and came up with this:
| | | |
| | | |
--- ( ( ---
---C1 ) ) ---C3
R1 | ( L1 L2 ) |
Vin---/\/\/\---| ) ( |------------->Vout
| | | | |
--- | | --- /
---C2 | | ---C4 \R2
| | | | /
| | | | \
R1=R2=50ohms for input and output impedance of 50ohms
C1=1.8p, C2=210p, L1=5uH.
L2 = 11.5uH, C3=0.8p, C4=92p
X1=53.125MHz, series resistance of X1=80ohms, shunt cap of X1=7pF, 3rd
Other parameters: bandwidth is 2 MHz around 53.125MHz.
The reason for getting rid of the two crystals in the original
3rd order design is because I really wanted the resonant frequency
to be at 53.125Mhz and to get rid of unrealistic cap values which
the AADE software found which also shifted down the resonant
The goal of my exercise is to have an input pulse to the filter ring
at the output at 53.125MHz for at least 250ns. In principle the
above filter should do this. However, although the sims don't look
too bad, I am quite worried about the maximum drive power of the
crystal which is only 100uW (yes, it is microwatts). Vin can be +/-
5V, and I doubt that the crystal can take it. I will probably have
to limit the power in with a >>50ohm resistor and use a transformer
to impedance match to 50ohms. Is this the way to go?
Do I need to worry that the crystal is a third overtone crystal rather
than a fundamental frequency crystal?
I have a funny feeling that I am missing other details which I'm
sure some of you with crystal filter designing experience can
Thanks for any help or info.
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup