Crystal Oscillator Circuit - Fujitsu F2MC-16LX Series Application Note

3. Crystal Oscillator Circuit

Figure 1 shows the oscillator for the Fujitsu 16-bit family. For best performance, the PCB
layout of this circuit should cover only a very small area. For the layout is recommended a
PCB with two or more layers. Make sure to provide bypass capacitors via shortest distance
from X0, X1 pins, crystal oscillator, and ground lines. The lines of the oscillation circuit should
not cross lines of other circuits.
Figure 1: Principle of the Oscillator circuit
It is necessary to avoid coupling noise into the power supply (pin 81/84) of the clock circuit.
The crystal oscillator has to be connected with short lines to X0/X1 and Vss. Note that pin X1
is the output of inverter. Particularly this track should have a short length.
Vss
X0
Connection to
C1
ground layer
Quartz
Crystal
a) Layout example for a leaded quartz crystal
layout design, because C1 and C2
worse
are wrong connected to VSS
Figure 2: Layout example for oscillator circuit
X0 X1
Oscillator
Decoupling capacitor C on
B
the back side of the PCB
C
B
Vcc
X1
Connection to
C2
ground layer
Quartz Crystal package
has to be grounded
Connection to
ground layer
Microcontroller
Via to ground island
and system ground
Vss
X0
SMD
Via to ground island
on the back side
Quartz Crystal
C1
b) Layout example for a SMD quartz crystal
better layout design, because C1 and C2
are connected to Vss and than after with
the system ground
Decoupling capacitor C on
B
the back side of the PCB
Via to system Vcc
C
B
Vcc
X1 Single ground island
on the back side
C2
5