SPK Product

Characteristics (for vcxo/tcxo/vc-tcxo)
  • Facebook
  • LINE
  • Twitter
  • LinkedIn

Characteristics for VCXO/TCXO/VC-TCXO

Characteristics

Specification
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)
  • 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.
  • Digital-TCXO
    Digital-TCXO has the excellent frequency stability by following procedure.
    1. Temperature sensor perceives ambient temperature.
    2. A/D converter converts temperature information into digital data.
    3. PROM generates appropriate programmed digital data for temperature compensation.
    4. D/A converter converts it into analogue data.
    5. 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
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.
Loading...