MC12061 Motorola, MC12061 Datasheet - Page 3

• Manufacturer Part Number: MC12061
• Description: (MC12060 / MC12061) Crystal Switching Methods
• Manufacturer: Motorola

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ing circuits. The Table II values have been take~,~$~j,re?*r-
In this case the devices are operating with a single cr~sta~$
connected
ence jn establishing the pulling (noted in T&ti~~~~d~used
by the switching networks. When using t~~~&~sti switch-
ing circuits,
resonant frequency is obtained by ~~~%~]~~ly adding the
respective values in Tables I and~$k~@~,.&xample, absolute
crystal pulling for the five cr~s?~,:,@tching
MC 12061. Measurements
for higher frequency crystals and will increase as the total
number of crystals. to be switched is increased. However,
by using the switching techniques shown in Figures 1 and
2, any frequency
crystal connected
caused by the ICS alone) ‘is negligible below approxi-
mately
summarized in Table 1. Typical frequency pulling values
Loading and therefore frequency pulling will be greater
1 MHz for the MC 12060 and 15 MHz for the
directly to pins 5 and 6 with no crystal @~~ch-
complete
pulling in addition
directly to pins S and 6 (i.e. pulling
Device
pulling from *’*hystd’s
..>>: ~t.$~<
of this additiond
...,,.!,,,.
to that for a single
.. .,! >,
k~), .@’*
I
system when
pulling are
series
MCI 2060
“
0.5
Where frequency pulling is not as critical, L1 in Figure 1
same diode current,
RF decoupling
R2, R4, R6, R8, and RIO and capacitors C6 through C 10.
may be eliminated.
cretion of the user.
both the MC 12060 and MC 12061 crystal switching cir-
cuits. Using a higher voltage supply for the bias networks
will allow larger values of bias resistors to be used at the
-0.0040
selecting the nominrd 1.0 MHz crystal is approximately
pulling for the 8.0 MHz crystal becomes -0.004 +0.0001
when selecting the 0.2 MHz crystal offset pulling caused
by the IC to give approximately
with the crystals and adjusted to pull the oscillq(lor up in
frequency.
= -0.0039
When desirable, a trim capacitor can be added in series
Several options are possible to reduce #~~~Ming
1.0
+‘ 0.0031 = -0.0009
percent. Pulling effects of the switching circuits
2.0
chokes may be added between resistors
resulting in reduced loading. Also,
These options
2.5
F:,
,,,,*&#@’l
percent. Similarly, absolute
:..,
%?S
zero absolute crystal pull.
,, : : ~ .. \
y
are left to the dis-
\
,?1.,
13.4
R .f
~},:,: ,, ~.,, \\$,,,
, ,, ~~.iv,
I
-0.005
20.0
n n..
Ref.
for