
PRODUCT SPECIFICATION
RC6508
7
Crystal Oscillator Internal Schematic
XTL-Tnk(3)
XTL-OUT(4)
Internal
GND-XTL (2)
V
CC
-XTL (1)
3.2K
2K
200
3.2K
6.8K
Q10
Q7
Q11
130
μ
A
100pF
230
μ
A
130
μ
A
450
μ
A
450
μ
A
Q12
Q18
Q17
L
3
L
2
C
3
C
2
47pF
C
5
C
6
C
8
+5V
VCC-XTL
(1)
VCO-IN (7)
8
μ
H
33
μ
H
0.1
μ
F
0.1
μ
F
1
μ
F
1
μ
F
C
7
C
4
1nF
1nF
The crystal oscillator is an ECL inverter. It is necessary to
bias the XTL-Tnk with a choke to 5V VCC_XTL power sup-
ply. The output is about 0.7V DC lower than VCC_XTL with
an approximate swing of 0.5Vpp at the output. If the oscilla-
tor is not used, it is good to ground XTL_Tnk pin.
VCO Internal Schematic
VCC_RF (6)
VCO_F
S
(8)
I
C
= 0.9MA
L
1
L
2
C
1
C
2
C
4
C
6
C
7
C
9
+5V
1
μ
H
33
μ
H
10pF
0.1
μ
F
0.1
μ
F
4.7
μ
F
1
μ
F
5pF
C
3
220pF
TO MIXER
Internal
+
–
VCO–In (7)
Q5
Q3
RFGND(5)
47.7
Q1
Q4
C
5
1nF
C
8
1nF
The VCO can be designed as a Colpitts oscillator. The above
circuit application shows VCO with adjustable typical value
of 38.75 MHz. The frequency is controlled by the external
resonance circuit. The oscillating transistor is Q1 in common
base configuration. To inject signal in the mixer in place of
LO, the VCO_Fs must be open. The signal on the pin
VCO_In should be under 100mVp-p and AC
coupled.