OCXO Vs VCXO Vs TCXO Vs DCXO - RF Wireless World

OCXO vs VCXO vs TCXO vs DCXO | difference between OCXO,VCXO,TCXO,DCXO

The page on OCXO vs VCXO vs TCXO vs DCXO covers difference between OCXO, VCXO, TCXO and DCXO crystal oscillators. Crystal oscillator is used as a frequency reference to generate very stable frequency source. It is used in many applications mainly frequency synthesizer, local oscillator and to provide stable clock in modem and other circuits.

Variation in temperature, supply voltage and ageing lead to drift in the crystal frequency output. The major change in the frequency output is due to temperature variation. It will change frequency to the high amount approx. about 10 PPM. By using OCXO and TCXO one can achieve stabilities in the order of about 0.0001 PPM.

OCXO

This page covers OCXO referred as Oven Controlled Crystal Oscillator. This type of oscillator is designed to operate inside temperature controlled oven. This maintains the temperature of crystal as well as oscillator circuit. The stability of this OCXO is better than all the other crystal oscillators. OCXOs are used in satellite, telecom and other applications requiring very high frequency stability frequency reference source. OCXO is available in difference output shapes viz. sine, square and HCMOS. It is available in different supply voltages viz. 12 V, 5 V and 3.3 V.

VCXO

This page covers VCXO referred as Voltage Controlled Crystal Oscillator. The change in crystal output is controlled using DC voltage. In the mobile phone design it is interfaced with DAC. This DAC is connected with micro-controller. Micro-controller provides digital input and DAC produces analog voltage output which controls the VCXO output. Hence any deviation in the frequency is compensated by voltage control pin.

TCXO

This page covers TCXO referred as Temperature Controlled Crystal Oscillator. This oscillator is designed to operate under larger variation in ambient temperature. The TCXO is housed with thermistor which takes care of continuous change in the surrounding temperature and controls the crystal oscillator.

VC-TCXO

Most of the GSM handsets use voltage-controlled temperature-compensated crystal oscillator (VC-TCXO) modules as the system reference oscillator. VC-TCXO modules use analog techniques to correct the frequency deviations. The problems of VC-TCXOs are their higher prices, larger footprint and need of external components on the circuit. These issues will introduce real concerns of smaller and cheaper mobile handset in the fast growing consumer market.

DCXO

This page covers DCXO referred as Digital Controlled Crystal Oscillator. In the present days, one alternative solution to the problem faced by VC-TCXO is to use digitally controlled crystal oscillator i.e. DCXO. Recent GSM mobile phone manufacturers are adopting DCXO in the design architecture to eliminate use of VC-TCXO. The success of DCXO entirely lies on frequency estimation, frequency correction and frequency tracking algorithms. DCXO is considered to be very stable compare to VCXO and TCXO.

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