Stephen,
Stephen said:
Does anyone know of a good tutorial or reference book that deals with
the theory and design of crystal filters?
Wes Hayward's RF circuit design book is good, although he uses a table-based
approach so if you're looking for the derivation of the necessary coupling
coefficients you'll have to consult his references. (Even when I was in
school, we were made to derive the '1Hz prototype filter' component values
in exactly ONE homework problem out of the dozens of filters we did as
homework. It's kinda tedious...and the homework problem was something
simple like a Butterworth filter as well. For elliptical filters, it's
quite involved to obtain the prototype values.) Anyway, though, a good
point about Wes's book in that he explains the physical meanings of the
coupling coefficient, which is useful in that a large number of books on
filter design assume you're going to be using LC-LC-LC... sections rather
than the LC-C-LC-... sections that are so much more attractive for Xtal
filter
Experimental Methods in RF Design (written by Wes Hayward, Bob Larkin and
Rick Campbell) has a fair amount of info as well. In many ways it's more
advanced that Wes's own book, and refers to that book as a reference. In
either case, be sure to check out Wes's web site
(
http://users.easystreet.com/w7zoi/w7zoi-page.html), because it has errata
and additional information.
This is a good general purpose link for filter design:
http://www.circuitsage.com/filter.html . If you're looking for a program to
do the design for you, the AADE Filter Designer listed is good, and while
the link says it's $25, these days it's actually free (Neil Heckt, Mr. AADE,
has a note about how he was making orders of magnitude more income from his
hardware products than from his software, so he decided to just make the
software free).
btw... I'm trying to design (and understand) a very narraw bandpass
filter (fc = 60khz for WWVB).
Cool, I'd love to see the results!
---Joel Kolstad
