CX8045JA View Datasheet(PDF) - Kyocera Kinseki Corpotation
Part Name
Description
Manufacturer
CX8045JA Datasheet PDF : 27 Pages
| |||
Handling Notes
(2) Changes of load capacitance and oscillation frequency
As shown above, the series resonance frequency of the crystal
unit changes with load capacitance CL of the oscillation circuit.
In the actual oscillation circuit, however, fine adjustments of
oscillation frequencies are carried out by varying CL by the
trimmer capacitor or the like. The following figure shows an
example of load capacitance characteristics. The slope of the
characteristics varies depending on the frequency, shape, the
number of overtone mode, etc.
3. Crystal oscillation circuit
(1) CMOS fundamental crystal oscillation circuit
As shown above, the series resonance frequency of the crystal
The figure on the right shows a standard CMOS inverter crystal
oscillation circuit for oscillating crystal unit with fundamental mode.
* Rx is an element to reduce excitation current of the crystal unit
preventing frequency fluctuation, but Rx is not used in some cases.
800
700
600
500
400
300
200
100
0
0
Load capacity characteristic
10
20
30
40
50
60
C L (pF)
CMOS fundamental crystal oscillation circuit
Rf = 1M
Buffer
Xtal
Rd
Rx
C1
C2
Characteristics of the circuit when load capacitances C1 and C2
are changed under the condition of C1 = C2 are shown in the
figure on the right.
It is not desirable that the excessive increase of the value of
condenser leads to a decrease of the negative resistance
resulting in increasing the possibility of oscillation failure.
Variation of negative resistance with condenser capacity
Condenser capasityC (C1=C2)(pF)
0
10
20
30
40
50
-100
-200
-500
-1K
-2K
()
-5K
-10K
16.0MHz
10.0MHz
3.579545MHz
Rd mainly adjusts frequency characteristics of the negative
resistance and is used to prevent oscillating by third Overtone
mode. In case of a bigger circuit of the negative resistance,
there is a case it is used to prevent the abnormal oscillation.
Frequency characteristics of negative resistance
Frequency(MHz)
2
4
6
8
10
12
14
16
-100
-200
-500
C 1= C 2=10pF
-1K
()
-2K
-5K
-10K
Resistance of Rd
3.5 to 6.9MHz=2.2k
7.0 to 16MHz=220
- 55 -
Share Link: 