Product Name: |
Characteristics |
Description: |
| TECHNICAL
TERMS |
| The following technical
terms are generally used for crystal oscillators: |
| Nominal frequency:
Nominal output frequency of a crystal oscillator |
| Frequency tolerance:
Deviation from the nominal frequency expressed in terms
of ppm |
| Operating temperature
range: Temperature range within which output frequency and other output
signal characteristics meet the specifications |
| Operable temperature
range: Temperature range within which crystal oscillators are still
operable despite the failure to meet the specifications |
| Temperature characteristics
(Frequency Stability): Rate of output frequency change at normal temperature
(25oC) given when only temperature is changed, with the other
conditions kept constant. |
| Frequency vs power
source variation characteristics: Rate of output frequency
change change given when only power source voltage is changed, with the
other conditions unchanged. |
| Short-term frequency
stability: Average of irregular output frequency fluctuations.
There are several measurement methods which provide different points of
view regarding irregularity. For crystal oscillators, either the definition
in the frequency demain or the definition in the time demain shall be
seleted. |
Harmonic distortion:Non-linear
distortion due to unwanted harmonic spectrum component related with target
signal frequencies. Each harmonic component is the ratio of electric power
against desired signal output electric power and is expressed in terms
of dB.
Ex.: 2nd harmonics.....-30dB or less |
 |
| TECHNICAL
TERMS |
| The
following technical terms are generally used for crystal oscillators: |
| Nominal
frequency: Nominal output frequency of a crystal oscillator |
| Frequency
tolerance: Deviation from the nominal frequency expressed
in terms of ppm |
| Operating
temperature range: Temperature range within which output frequency
and other output signal characteristics meet the specifications |
| Operable
temperature range: Temperature range within which crystal oscillators
are still operable despite the failure to meet the specifications |
| Temperature
characteristics (Frequency Stability): Rate of output frequency change
at normal temperature (25oC) given when only temperature is
changed, with the other conditions kept constant. |
| Frequency
vs power source variation characteristics: Rate of
output frequency change change given when only power source voltage is
changed, with the other conditions unchanged. |
| Short-term
frequency stability: Average of irregular output frequency
fluctuations. There are several measurement methods which provide different
points of view regarding irregularity. For crystal oscillators, either
the definition in the frequency demain or the definition in the time demain
shall be seleted. |
Harmonic
distortion:Non-linear distortion due to unwanted harmonic spectrum
component related with target signal frequencies. Each harmonic component
is the ratio of electric power against desired signal output electric
power and is expressed in terms of dB.
Ex.: 2nd harmonics.....-30dB or less |
|
| CRYSTAL
OSCILLATORS |
| Temperature compensated crystal
oscillators (TCXO) |
| a) TXCO |
The temperature characteristics
of crystal oscillators are, for the most part, dependent upon those of
crystal units used which are generally expressed by cubic curves (AT-cut).
Obtaining superlative temperature characteristics requires the operating
temperature ranges to be limited or the ambient temperatures to be kept
constant by means of a constant temperature oven.
With TCXO, temperature compensating circuits are built-in to get excellent
temperature characteristics over a wide temperature range.
The temperature compensating circuit performs the function of compensating
the temperature characteristics of crystal units by the combination of
exponential-function based temperature detecting elements and resistances.
That is why the resultant temperature detecting elements and resistances.
That is why the resultant temperature characteristics differ depending
upon the combination of compensatng circuits or the specified temperature
range. In general, temperature characteristics are expressed by 3rd to
5th order curves.(See Fig. 2.)
TCXO feature excellent temperature characteristics, low power consumption,
light weight, compactness and fast warm-up, and are ideally suited for
various communications equipment (car telephones, walkie-talkies, MCA,
cordless telephones, microwave communications equipment and satellite
communication system) and measuring instruments (frequency counters, frequency
synthesizers, etc.) as standard oscillators.
|
| b) Digital-TCXO |
Digital-TCXO has the
excellent frequency stability by following procedure.
- Temperature sensor perceives
ambient temperature.
- A/D converter converts temperature
information into digital data.
- PROM generates appropriate programmed
digital data for temperature compensation.
- D/A converter converts it into
analogue data.
- Variable capacitance diode is
controlled by analogue data and VCXO oscillates proper frequency.
|
| Voltage controlled
crystal oscillators (VCXO) |
| With VCXO, the connection
of a variable capacitance diode with a crystal unit in series causes the
diode capacitance to be changed in accordance with the voltage applied
for frequency control, thus pulling frequency corresponding to the load
capacitance characteristics of crystal units. Our VCXO feature superlative
linearity realized by the proper combination of the applied voltage and
capacitance characteristics of a variable capacitance diode with the load
capacitance and oscillation frequency characteristics of crystal units. |
| The temperature characteristics
of VCXO are the same as those of SPXO and are ideally suited for PLL,
AFC, circuit servo system, FM modulator, sweep generator, etc. |
| APPLICATION
NOTE |
| *Electrical |
- Power source
Be sure to connect the poralities to specified terminals correctly.
Reversed connection or connection to a wrong terminal not specified
may cause the parts used in a crystal oscillator to be damaged or
result in non-oscillation. Applying rated-value exceeding voltage
may cause the same failure, Be sure to use a crystal oscillator at
the rated voltage. If the applied voltage is less than the rated value,
the oscillator may not satisfy the specified performance despite the
fact that the parts in the crystal oscillator are not damaged.
- Load impedance
Connection of a crystal oscillator should be made in terms of specified
load impedance. The connection in terms of unspecified load capacitance
may result in the unspecified output frequency and output level or
cause distorted wave-from to produce troubles. Especially for the
load impedance reactance, the adjustment to the specified value is
essential.
- Output frequency and level
Measure the output frequency and output level of a crystal oscillator.
And at the same time, adjust the input impedance of a measuring instrument
in such a way that it equals the load impedance of a crystal oscillator.
The following figure shows the case where the input impedance of a
measuring instrument is different from the load impedance of a crystal
oscillator. In such a case, it is necessary to make measurement in
terms of high impedance sufficient for neglecting the impedance on
the measurement system side.
Z: Load impedance of a crystal oscillator
|
| *Mechanical |
- Shocks
Do not cause strong shocks. When carrying or attaching a crystal oscillator,
be creful not to drop it or hit it a hard object.
If strong shocks are caused, please check its performance prior to
use.
- Attachment method
Be careful not to give strong force to the terminals or the attachment
screws of a crystal oscillator.
In the case of attaching a crystal oscillator to a PC board, the distance
between holes should equal the distance between the terminals of the
crystal oscillator. If these distances are not equal to each other,
forced attachment may cause the terminals to be broken.
Do not bend the terminals of a hermetic-sealed crystal oscillator
Whose diameter exceeds 0.6mm. Even in the case of a terminal whose
diameter is less than 0.6mm, be careful not to bend a terminal at
the root directly. The specifications of fastening torque are as shown
below:
| Screw
diameter |
Fastening
torque |
| M2.6 |
4kg.cm |
| M3 |
5kg.cm |
| |
- Cleaning
Do not soak a crystal oscillator in the liquid when cleaning it.
|
|
|
|
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