TK83361M 查看數據表（PDF） - Toko America Inc
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TK83361M Datasheet PDF : 15 Pages
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TK83361M
APPLICATIONS INFORMATION (CONT.)
(1) Using an External Oscillator Source
The circuit composition using an external OSC source is
shown in Fig. 4. When using an external OSC source
instead of the internal OSC, the local level must be injected
into Pin 1 by capacitor coupling.
In this case, Pin 2 must be open.
The local OSC operates as an emitter follower for a multi-
plier by opening Pin 2 and injecting into Pin 1.
Figure 4: External Injection
tor. It is easy to increase the drive current by connecting
resistor Re between Pin 2 and GND. Being short of drive
current, it makes gm increase to increase the drive current
by connecting external resistor Re. In that case, the amount
of drive current increase, Ie, is shown in Eq.(1).
Ie = VCC VBE = VCC 0.7
(1)
Re
Re
VCC
50Ω
~
0.01µ
1
50Ω
2
open
RF
IF
(2) For 3rd Overtone mode
In general, a crystal oscillator can oscillate in the fundamen-
tal mode and overtone mode. For example, it is easy for a
30MHz-overtone crystal to oscillate at 10MHz, fundamental
mode. The reason is because the impedance of the funda-
mental mode is the same as the impedance of the overtone.
Therefore, it is necessary for the circuit to select the
overtone frequency by using a tuning coil.
How to oscillate a general 3rd overtone oscillator is ex-
plained. In the case of an overtone mode of 30MHz and
higher, using a crystal oscillator, we recommend the circuit
in Fig. 5 to suppress the fundamental mode oscillation.
In order to oscillate at the 3rd overtone frequency, the values
of C2, C3 and L (Fig.5) are selected. Fig.6 shows a 2-port
impedance response of the C2~C3~L loop network.
Regarding the condition of oscillation, the impedance char-
acteristic is capacitive at the vacinity of the overtone fre-
quency. It is reactive at the vicinity of the fundamental
frequency.
The condition of oscillation is as follows:
fOSC is between fa and fb,
3 x fOSC is fb and higher. Please see Fig.6
Figure 6: 2-port
Impedance Response of Resonance Network
+j
fOSC
fa
fb
3 X fOSC
-j
Where:
fa: series resonant freq.
fb: parallel resonant freq.
fOSC: fundamental mode freq.
3 x fOSC:
3rd order overtone freq.
Equations of 3rd order overtone oscillation are shown below.
Figure 5: Overtone Mode Circuit
VCC
1
fa =
2π LxC2
, fb = fa
1+ C2
C3
(2)
X’tal
1
C2 L
C1
2
C3
Re
The following explains how to decide the circuit constants of
the overtone-crystal-oscillation fundamental circuit.
As the operating frequency increases the oscillation ampli-
tude decreases because of a shortage of gm of the oscilla-
The series value of the equivalent capacitance at the 3rd
order overtone freq. of this network, which is decided in the
above -mentioned, and the capacitance of C1 must be equal
to load capacitance CL.
Being short of negative resistance of the circuit, increase
the transistor’s bias current by decreasing Re. It is able to
decide the OSC level for minute adjusting Re. Please refer
the most suitable OSC level range to 12dB SINAD sensitiv-
ity versus local OSC input signal level in TYPICAL PER-
FORMANCE CHARACTERISTICS. The saturating range
is the most suitable OSC level range. It is comparatively
easy to decide the circuit constant by examining it with a
network analyzer.
December 2000 TOKO, Inc.
Page 11
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