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From: Tony Williams
Subject: Re: Querry, Kick Starting Crystal Oscilator.
Date: Mon, 11 Nov 2002 16:45:07 +0000 (GMT)
References: <3DCA905A.59FD928B@mmm.com.DELETETHIS> <3DCC9A71.7DF3C3A9@mfi.net> <firstname.lastname@example.org> <3DCFC4EF.7C9781B8@mmm.com.DELETETHIS>
NNTP-Posting-Date: Mon, 11 Nov 2002 16:45:51 +0000 (UTC)
User-Agent: Pluto/1.14i (RISC-OS/3.60)
In article <3DCFC4EF.7C9781B8@mmm.com.DELETETHIS>,
Roy McCammon wrote:
> Tony Williams wrote:
> > ---+--Lf----Cf----/\Rs/\---+----
> > | |
> > +-----C0----------------+
> hmmm. Is this R the crystal series resistance?
The R is the general series-resistance of any
RLC series-tuned circuit and the RCA book does
state that Rs is the series resistance of the
crystal. Their sample crystal had Rs=40k, Lf
= 4800H, Cf= 0.00491pF, C0= 2.85pF and Q= 25000.
They further reduced that 4-element circuit
above to a 2-element.... +---/\/\---[Xe]---+
By itself that equivalent circuit had Xe= 0
at 32760Hz and 32790Hz. Re was about 35k at
32760Hz and about 6E7 ohms at 32790hz.
When loaded with an external 10pF, Xe equalled
the reactance of the 10pF at 32768Hz. Re was
about 70k at 32768Hz.
> > Ratio= exp(-pi*R/w*L)
I searched for that sum because I did faintly
remember that the rate-of-change of amplitude
of any tuned circuit depends on the Q, high
Q makes it slow to move the amplitude. That
was the reason for going on about trying to
temporarily reduce the Q (of the pi-network).
Might be worth trying a resistor in series
with the crystal to see if that increases the
effective Rs (as far as the pi-network is
concerned), and lowers the Q temporarily.
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