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Quartz Crystal Oscillator

   
The basic principle

When an external one hit, immediately after the collision the short-term oscillations, and soon after, reverted the original static state, the free oscillation frequency, that is called the resonant frequency. Having two parallel surfaces in a thin, when there is parallel to the surface of the plane wave is present, then the wave that is reflected back and forth at the ends. Plate thickness to when an integer multiple of half the wavelength of the reflected waves back and forth, back and forth of the plane wave phase, forming standing waves and amplitude of the plate surface. When the thickness is half the wavelength of a plane wave, which is the base of thickness-shear-mode frequency (fundamental thickness-shear mode)。
Quartz chip itself is a piezoelectric material (piezoelectric material), with external voltage is applied to produce electric fields on both sides of the chip, due to mechanical and electrical coupling of piezoelectric materials, mechanical deformation of the Crystal itself, role of the mechanical stress on the cutting surface by Crystal, crystals of opposite phase will produce a potential difference.

When on both sides voltage transistor AC voltage, as shown in the following figure, y cut quartz plate on the x-z plane of vapor deposition electrodes to generate a cycle of oscillation of chip. Oscillation frequency will vary according to the thickness of the Crystal, quartz crystal cut more, cut more difficult, but the higher the resonance frequency。

石英平板配置圖
y Cut quartz plate configuration (length of 2A) (polarization direction is along the y axis)
Equivalent circuit simulation

Usually oscillators can take advantage of capacitor (c) and inductor (l) and resistance (r) of circuit simulation, impedance matching are the frequency diagram. Take the effect of oscillation circuit simulation can be seen. The equivalent circuit diagram is as follows,
等效電路
Real Crystal, there are many State induces changes in the frequency of operations, including: operating temperature, the capacitance of the load (Load Capacitance), driving standards (Drive Level).

Frequency stability of quartz substrate and tangential, angle, size of operation modes and quartz. In the above illustration two resonant frequency of the circuit simulation. Quartz crystal showing series and parallel resonance (as shown in the left picture below). Quartz crystal impedance and frequency of operation is like a right relationship.。
石英晶體的阻抗和操作頻率

Equivalent circuit simulation
Thickness-shear frequency ( TSf ) Thickness of torsional mode Three times harmonic mode ( TS3 )
厚度剪切基頻 ( TSf ) 厚度扭轉模態 厚度扭轉模態
In what cases replaced X'tal OSC must satisfy conditions?
【Confirm the original loop】
  first this star CHIP SET of OSC INPUT of conditions whether meet replaced, that is this star CHIP SET whether has shocks loop of based component. and these component must to has a only reverse device, a buffer (also can by two star reverse device to frame loaded into a buffer), this is most basic of up vibration of active component. This can by CHIP SET DATA SHEET Shang learned that, or by CHIP SET of OSC PIN Shang confirmed know, OSC INTPUT 2 to PIN, its marked as Xin and Xout said within the onset of active components. Conversely, only has 1 input external oscillation loop circuits. Out of this initiative must be, need a few passive capacitor two resistors with two X'TAL is three times the frequency that is about to add another ㄧ only capacitors and notwithstanding the inductance, the two values and oscillator
【XTAL electrical parameters】 
  • Confirm XTAL Frequency Tolerance.
  • XTAL Blank cutting angle: the offset affects the frequency under different temperature
  • the size of the electrode surface: effects of impedance (RR) and the second wave (Spurious) properties.
      Internal impedance caused by following factors to:
    • Blank Parallelism of surface
    • The Blank roughness
    • Blank Surface contamination
    • BaseSelect
    • AU Selection of epoxy adhesives
    • Glue size and position
    • Evaporation volume size
    • Amount of fine tuning
    • Electrode size trimming size
    • Fixed chip shape of the Base bracket
    • Sealing conditions
    • N2 Purity and content
  • DLD2,FLD2,RLD2 : Will affect the stability of electrical characteristics..
【Word of advice】
  • Costs
    • With XTAL OSC uses a different combination of Chip Set, so the Chip Set price also has gaps
    • Internal use IC to integrate the XTAL OSC match XTAL*1pcs in the circuit, capacitance *2pcs resistance *2pcs, reverse *1pcs, buffer *1, if replaced by XTAL OSC to do actuarial required materials list price to get the most economical cost
  • In terms of technology integration
    • OSC application directly on the PCB Board, adjust the frequency
    • XTAL oscillator circuit needs to be done in the matched combination of load capacitance Cg,Cd, in order to achieve the correct frequency output
    • XTAL OSC output square wave is black wave
    • OSC The intensity of the output voltage level
 

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