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TYPES OF QUARTZ CRYSTALS
Quartz (SIO2) is composed of two elements, Silicon and dioxide.
Quartz crystals are an indispensable component of modern electronic technology.
They are used to generate frequencies to control and manage virtually
all communication systems. They provide the isochronous element in most
clocks, watches, computers and microprocessors.
Quartz crystals (crystals units) are produced from crystal
element cut out at a direction predetermined in accordance with the purpose
for which they will be used. Fig.2 and Fig.3 show the cut mode of vibration,
frequency range and characteristics.
FREQUENCY VS. TEMPERATURE
CHARACTERISTICS
a. AT-cut crystal.
A special cut angle for quartz plate that has excellent performance in
temperature characteristics of frequency. See Fig.1.
b. Various cut crystal frequency characteristics.
See Fig.2.
l THE CRYSTAL ORIENTATION ANGLE AND MODE OF
VIBRATION
See Fig.3 ＆ Fig.4.
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EQUIVALENT CIRCUIT
OF QUARTZ CRYSTAL UNIT
A quartz crystal unit in the near main resonance frequency, may
be expressed as an electrical equivalent circuit-a circuit ordinarily
composed of a series circuit consisting of an inductance, capacitance
and resistance, and a capacitance connected in parallel to the series
circuit as shown in the drawing.
Here, Co, which is commonly known as the shunt capacitance, comprises
an inter-electrode static capacitance to which the inter-terminal
stray capacitance is added.
L1 and C1 are the equivalent constants of the quartz crystal unit
as viewed as an electrical and mechanical oscillation system. Since
both constants are determined by such factors as the type of cut,
cutting angle, dimensions of the crystal piece, and construction
of the electrodes, and are thus reproducible, quartz crystal units
can be manufactured to high precision.
R1, which denotes oscillation loss, is governed by such conditions
as the cutting method, holding method, shape and dimensions of the
quartz crystal.
L1 is known as the motional inductance, C1 the motional capacitance,
and R1 the series resistance.
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Electrical equivalent
circuit of quartz crystal unit.
L1: motional inductance
C1: motional capacitance
R1: resonance resistance, equivalent series resistance
C0: shunt capacitance
The electrical equivalent
circuit, composed of L1, C1, R1 and C0, all of which are correlated,
may be expressed by the following equation.
Shown below are some
equations by which the performances of quartz crystal units are
expressed.。
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