技術辞典

Because of excellent stability, the crystal oscillators are widely applied in the fields of communications, measurement, clock, control devices and so on where frequency output with high accuracy is required. With the requirement of frequency stability becoming stricter, it is better to choose purchase of oscillators than the crystal units on many occasions, for frequency output with high stability can be easily acquired with power voltage supplied only to the oscillator. Here we would like to mention that crystal oscillator refers to the combined unit of crystal units and the amplifier with feedback circuit.

The Main Types of Crystal Oscillator 

1. General Crystal Oscillator 

Basically this type of oscillator is composed of the crystal unit and feedback amplifier that operates the crystal unit. There are different output waves corresponding to different applications.

2. Voltage-Controlled Crystal Oscillator=VCXO 

VCXO is the oscillator with the function of adjustable control of output frequency added to the General Crytal Oscillator by use of external control voltage.

3. Temperature-Compensated Crystal Oscillators, TCXO, VC-TCXO 

The biggest factor that affects the frequency stability is the temperature characteristics. With the help of temperature-compensated circuit, this type of oscillator realizes higher stabilization of temperature characteristics than the crystal unit. Because the specified temperature-compensated voltage is applied, TCXO can output much more stable frequency against the ambient temperature. It is mainly applied for the standard oscillator used for frequency synthesizer of mobile communications device. PDC (Personal Digital Cellular), GSM (Global System for Mobile Communication), GPS (Global Positioning System) and so on require frequency with high temperature stability of +/-2.5ppm Maximum. Such requirement cannot be satisfied with the AT cut crystal unit only. Moreover, there is subtle difference with different crystal units in temperature characteristics. So, there is need to make compensation with the temperature compensation circuit in order to acquire frequency of high temperature stability. 

Application: Digital TV-tuner (SCV- 3225 size) 

EX: SCV- 3225 27MHz Characteristics as following charts

Application：GPS (5032size TCXO) 

TXO83 16.367600MHz as following drawings show characteristics

Application：PDC (3225size VC-TCXO) 

TXO92 14.400MHz as following drawings show characteristics

Application : Wireless LAN / High Precision ±5ppm 

OSC73 5032 size (CMOS output) as following drawings show characteristics

     In the past, the Bus interface of PC had been quick moving from drive voltage 5V of TTL and CMOS to drive voltage 3.3V of LVTTL and LVCMOS which are the mainstream. Recently people disire mostly the high speed of Bus interface and develop successfully Giga Ethernet Technology which can transmit Gbps. However, under gigabyte transmission, the Clock will be over 100MHz even higher, the Noise influence will be very obvious. For providing a good quality crystal oscillator, SIWARD developed triumphantly OSC57A, OSC57B and SEV-7050. Those interface is differential interface of LVPECL and LVDS. Moreover, those can be used in high speed transmission without Noise influence. 

 Differential signal transmissioncan lower Noise influence.

The following diagrams indicate the LVPECL and LVDS.

Block Diagram of Programmable Oscillator SPO-7050B, SPO-5032B

Comparison (Jitter)  Example: 106.25MHz 

OSCs test circuit of CMOS output 

Model: OSC52, OSC71, OSC73, OSC81, STO-3225B, SHO-3225, SCO-2520, SCO-2016.

Model: SFO-3225 (SCO-3225C)

OUTPUT WAVEFORM

VCXOs test circuit of CMOS output

Model: VCX91, VCX92, VCX95, SCV-3225

OUTPUT WAVEFORM

OSCs test circuit of TTL output 

Model: OSC52, OSC71

OUTPUT WAVEFORM

TCXOs and VC-TCXO test circuit of Clipped Sine output 

Model: TXO83, VTX83, TXO92, VTX92

OUTPUT WAVEFORM

LVPECL 

Model: OSC57A

OUTPUT WAVEFORM

LVDS 

Model: OSC57B

OUTPUT WAVEFORM

Emboss Taping and Reel Specifications