Handling Notes
800
700
600
500
400
300
200
100
0
(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.
Load capacity characteristic
0
10
20
30
40
50
60
L (pF)
C
3. Crystal oscillation circuit
CMOS fundamental 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.
Rf=1M
Buffer
Xtal
Rd
Rx
C
1
C
2
Characteristics of the circuit when load capacitances C
1
and C
2
Variation of negative resistance with condenser capacity
are changed under the condition of C
1
= C
2
are shown in the
Condenser capasityC (C1=C2)(pF)
figure on the right.
0
10
20
30
40
50
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.
-100
-200
-500
16.0MHz
10.0MHz
-1K
-2K
3.579545MHz
()
-5K
-10K
Frequency characteristics of negative resistance
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(MHz)
2
4
6
8
10
12
14
16
-100
-200
-500
C1=C2=10pF
-1K
-2K
()
Resistance of Rd
-5K
3.5 to 6.9MHz=2.2k
-10K
7.0 to 16MHz=220
- 55 -
KYOCERA AVX [ KYOCERA AVX ]
