Basics and types of TCXO | ADTCXO, DTCXO, DCXO, MCXO difference
The page describes basics and types of TCXO. It compares TCXO types viz. ADTCXO vs DTCXO vs DCXO vs MCXO and mentions difference between ADTCXO, DTCXO, DCXO and MCXO type.
Definition: The term TCXO stands for Temperature Compensated Crystal Oscillator. As the name suggests the crystal oscillator which does compensation of its frequency response with surrounding ambient temperature variation is known as TCXO.
It is widely used in wireless and other industries and found in mobile phones, PDAs etc. The figure-1 depicts TCXO working with uncompensated and compensated frequency responses. TCXO uses additional circuitry to compensate for its frequency with temperature variation.
TCXO offers superior temperature performance on the order of 10s to 40 times better compare to normal crystal oscillators. They are available in various package types and provides clipped and normal sine wave outputs. Most of the crystal oscillators are powered using 3V supply and draws just about 2 mA of current.
The figure-2 depicts simple analog TCXO type. Based on analog, digital and analog/digital compensating network there are many types of TCXO as outlined below.
Following are the features of ADTCXO :
• The term ADTCXO stands for Analog Digital Temperature Compensated Crystal Oscillator.
• It uses analog techniques to compensate frequency of oscillator as per temperature variation.
• The output changes slowly and abrupt change like some of the digital oscillators is not observed here.
• It is widely used in cellular phones.
Following are the features of DTCXO :
• The term DTCXO stands for Digital Temperature Compensated Crystal Oscillator.
• It uses temperature sensor and DAC along with logic functions to compensate frequency as per ambient temperature variation. The figure-3 depicts digital TCXO type.
• Here temperature sensor senses ambient temperature. This input is used by logic circuitry along with look up table which gives out appropriate digital value to be provided as compensation value. This digital value is converted to analog value using DAC converter and provided to crystal for frequency correction.
Following are the features of DCXO :
• The term DCXO stands for Digitally Controlled Crystal Oscillator.
• It uses algorithms such as frequency estimation, correction and tracking algorithms.
• It is very stable oscillator compare to VCXO and TCXO types.
• It is widely used by GSM mobile phone manufacturers.
Following are the features of MCXO :
• The term MCXO stands for Microprocessor Compensated Crystal Oscillator.
• It uses microprocessor to provide high processing capabilitites to provide very efficient compensation.
• ADC is used along with DAC in place of look up tables.
• It delivers better performance but at the cost of increased price compare to other types.