Technical Informations

 

CRYSTAL UNIT a thickness shear vibrator device(frequency is determined by the crystal thickness), is an essential
frequency control device used in TV, VTR, COMPUTER, MICROPROCESSOR, CAR PHONE, wireless telephone, quartz
watches, toys, AUDIO SYSTEM including all sort of electronic home appliance, variety of communication and electronic
equipments.

Even with surrounding temperature and environment change, and after long time use, it supplies very stable precise
frequency. It is an essential product. Without it, current developments in civilization would have never happened.

Main Characteritic to select a crystat unit

Characteristic UNIT
Package HC49/U Serie-UM serie-7x5mm-5x3.2mm...
Nominal Frequency MHz
Vibration Mode Fundamental Fundamental, 2nd , 3th
Oscillation mode Parallel or serie
Frequency Tolerance (@25°C±2°C) ppm
Frequency Stability ppm
Operating Temp. Range °C
Load Capacitance 16 pF
Serie resistance max. Ohms
Shunt capacitance (Co) pF max
Aging ppm/year

CRYSTAL OSCILLATORS combines Crystal unit, IC, and other circuits. It is small yet can obtain stable frequency
even there is environmental change. In COMPUTER, it is a core component used for character construction, color
construction circuit.

One step ahead of crystal oscillator, voltage compensated crystal oscillator(VCXO), temperature compensated
crystal oscillator (TCXO), and oven controlled crystal oscillator(OCXO) are core components which are used as a
standard in all signals, space satellites, and measuring devices.

Electronic Connotation Specific frequencies voltage or electric current creating device (comprehensive).

Combines crystal unit, IC, and other circuits to provide high stability oscillating frequency (signal) creating active
device(significant).

Standard construction of Oscillating circuit Crystal Oscillating Circuit is constructed by combined circuit of frequency
creating blank (=BLANK , crystal), Rf ( Feedback Resistor ), amplification device and Capacitor.

Crystal oscillators construction.

 

 

OSCILLATION FREQUENCY & LOAD CAPACITANCE

Electronic Connotation Specific frequencies voltage or electric current creating device (comprehensive).
Combines crystal unit, IC, and other circuits to provide high stability oscillating frequency (signal) creating active
device (significant).

Standard construction of Oscillating circuit Crystal Oscillating Circuit is constructed by combined circuit of frequency
creating blank (=BLANK , crystal), Rf ( Feedback Resistor ), amplification device and Capacitor.
Crystal oscillators construction

 

Oscillation Frequency and Load Capacitance In an oscillation circuit in which a quartz resonator works as inductive
impedance, the equivalent circuit is indicated by the engative resistance and capacitance, as shown in Fig. 5.

Fig. 5 (a) expresses the oscillation circuit with a series circuitry, while (b) expresses a parallel circuitry.
Here the capacitance CL is an effective capacitance when the oscillating side is viewed from the ends of the
quartz resonator, usually called a load capacitance, and -R and - p are negative resist-ances of the oscillating side.

In this type of oscillation circuit, the quartz resonator works as a series circuitry of an inductive reactance Xe and
a resistance Re, as shown in Fig.6 and its oscillation frequency is expressed by:

 

The conditions for oscillation to start is 1 Re 1 < 1 R 1 in the case of (a), and 1 Rp 1 > 1 p 1 in the case of (b),
where Re is the series resonant resistance (equivalent series resistance) of the series circuitry of a quartz
resonator and capacitance CL, and Rp is the parallel resonant resistance (equivalent parallel resistance) of the
parallel circuitry of quartz resonator and capacitance CL.

In order to have certain oscillation while increase of the equivalent resistance at a low excited level of the quartz
resonator is taken into consideration, the negative resistance (-R) of the circuit must be good deal larger compared
with Re.                      

Thus the oscillation frequency is decided by the electrical equivalent constant of the quartz resonator and the load
capacitance of the oscillating side regardless of configuration of the oscillation circuit (operating temp. and exciting
level to be specified separately), so that the load capacitance of the oscillation circuit must be defined clearly at the
time of manufacture or use.

The equivalent circuit of the quartz resonator and a series connected load capacitance CL is expressed AS in Fig. 7,
and constants at this time are as follows:

 

The oscillation frequency at this time is increased by µf, and we have:

 

where ¡µf is the difference from the frequency Fo in series resonance. Re-arrangement of this equation will yield the
following equation:

 

Where CO/C1 is called the capacitance ratio, The capacitance ratio serves as a reference for knowing the size of the
amount of change in the oscillation frequency due to alteration of the load capacitance.

Fig 8 shows the load capacitance vs frequency change ratio characteristic of a fundamental AT cut resonator and a
3rd overtone resonator. It is required, as shown by the Fig 8 to use a fundamental resonator and select a small load
capacitance in order to obtain the amount of change over a wide frequency range through changing of the load capacitance.


Crystal Oscillator characteristics' standard terms

Frequency Stability Center frequency variation according to changes in Temperature, voltage , Output Load. (Unit: ppm)

Operating Temperature range The temperature range which the oscillator frequency and waveform operate safely
within the set¡¯s permitted temperature limit (Unit: C)

Rise Time (Tr) The time it takes for the output waveform to change from low to high level. (Unit : nsec)

Fall Time(Tf) The time it takes for the output waveform to change from the high voltage level to low voltage level. (Unit : nsec)

Duty Cycle(Symmetry) Measured at +1.4V for TTL oscillators and 1/2 Vdd level for universal, HCMOS and CMOS oscillators,
this is the ratio of full and half cycles

Input current The amount of current consumption by an oscillator from the power supply, typically specified in milliamps (mA ).

Standby function(E/D, Tri-state) Oscillator Optional function, it temporarily stops oscillation when the set function desires it.

MONOLITHIC CRYSTAL FILTER Applied crystal unit, it has two electrodes thus forming two specified frequency,
filters several frequencies to allow only the desired frequency to pass through and holds the unwanted frequency
to eliminate mixing, crossing, noise, and interference in communication devices and increase the transmission intensity.

Generally, portable cellular phone gets smaller but have clean communication quality, this is because of monolithic
crystal filter.
Monolithic Crystal Filters are used in radio(wireless) communication, space satellites, pager, fish detector, cellular
telephone, all sort of communication devices and electronic devices.

 

TERM DEFINITION
NOMINAL FREQUENCY Specified Center Frequency.
PASS BAND WIDTH The frequency band width in which the attenuation is same or less than a specified value A.
Pass band width is specified by minimum value.
STOP BAND WIDTH The frequency band in width in which the attenuation is equal to B, B is specified by maximum value.
RIPPLE Within a pass band, the difference between maximum and minimum attenuation.
INSERTION LOSS The transmitted power difference between a filter inserted and not.
ATTENUATION GUARANTEED The minimum attenuation guaranteed at stop band.
SPURIOUS RESPONSE Minimum attenuation caused by unusual response in the stop band.
TERMINAL IMPEDANCE A signal impedance and a load impedance of a filter.