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Tel: +44 (0)1460 230000 Fax: +44 (0)1460 230001
info@euroquartz.co.uk
www.euroquartz.co.uk
EURO QUARTZ
CRYSTAL EQUIVALENT CIRCUIT
R1 Motional Resistance
L1 Motional Inductance
C1 Motional Capacitance
C0 Shunt Capacitance
TERMINATIONS - PLATING
SM1
Gold Plated (Lead Free)
SM2
Solder Plated
SM3
Solder Dipped
SM4
Solder Plated (Lead Free)
SM5
Solder Dipped (Lead Free)
Designation
Termination
TYPICAL APPLICATION FOR A
PIERCE OSCILLATOR
The low profile CX miniature crystal is ideal for use in small, high
density, battery operated portable products. The CX crystal designed
in a Pierce oscillator (single inverter) circuit provides very low current
consumption and high stability. A conventional Pierce oscillator is
shown above. The crystal is effectively inductive and in a Pi network
circuit with CD and CG provides the additional phase shift to sustain
oscillation. The oscillation frequency (fO) is 15 to 250ppm above the
crystal's resonant frequency (fS).
Drive Level
RA is used to limit the crystal's drive level by forming a voltage divider
between RA and CD. RA also stabilizes the oscillator against changes in
the amplifier's output resistance (RO). RA should be increased for
higher voltage operation.
Load Capacitance
The CX crystal calibration tolerance is influenced by the effective
circuit capacitances, specified as the load capacitance (CL). CL is
approximately equal to:
Note: CD and CG include stray layout-induced capacitance to ground
and CS is the stray shunt capacitance between the crystal terminal. In
practice, the effective value of CL will be less than that calculated from
CD, CG and CS values because of the effect of the amplifier output
resistance. CS should be minimized.
The oscillation frequency (fO) is approximately equal to:
CL
D
G
S
C
=
x
+
D
G
+
f O
S
1
L
= f
+
2(CO + C )
C1
Where
FS = Series resonant frequency of the crystal
C1 = Motional Capacitance
CO = Shunt Capacitance
CONVENTIONAL CMOS PIERCE OSCILLATOR CIRCUIT
CX4VSM CRYSTAL
Ultra-Miniature SMD Crystal
30kHz to 250kHz