RFTCXO Types: ADTCXO, DTCXO, DCXO, MCXO Differences
This page describes the basics and different types of Temperature Compensated Crystal Oscillators (TCXO). It compares various TCXO types, specifically ADTCXO vs. DTCXO vs. DCXO vs. MCXO, highlighting the differences between them.
Definition:
TCXO stands for Temperature Compensated Crystal Oscillator. As the name suggests, it’s a crystal oscillator that compensates for frequency variations caused by changes in the surrounding ambient temperature. TCXOs are widely used in wireless communication and other industries, commonly found in mobile phones, PDAs, and other devices.
Figure 1 illustrates the working principle of a TCXO, showing both uncompensated and compensated frequency responses.
TCXO working operation
TCXOs employ additional circuitry to compensate for frequency drift due to temperature fluctuations. They offer superior temperature performance, typically 10 to 40 times better than standard crystal oscillators. They are available in various package types and provide both clipped and normal sine wave outputs. Most crystal oscillators operate using a 3V supply and draw approximately 2mA of current.
Analog TCXO type
Figure 2 depicts a simple analog TCXO. Based on the type of compensation network (analog, digital, or a combination of both), there are several TCXO types, as detailed below.
ADTCXO
The following are key features of an ADTCXO:
- ADTCXO stands for Analog Digital Temperature Compensated Crystal Oscillator.
- It utilizes analog techniques to compensate for the oscillator’s frequency based on temperature variations.
- The output changes gradually, avoiding abrupt shifts characteristic of some digital oscillators.
- It is widely used in cellular phones.
DTCXO
Digital TCXO-DTCXO
The following are key features of a DTCXO:
- DTCXO stands for Digital Temperature Compensated Crystal Oscillator.
- It uses a temperature sensor, a DAC (Digital-to-Analog Converter), and logic functions to compensate for frequency changes due to ambient temperature variations. Figure 3 illustrates a typical digital TCXO.
- A temperature sensor detects the ambient temperature. This input is processed by logic circuitry and a lookup table, which outputs an appropriate digital value for compensation.
- This digital value is converted to an analog signal using a DAC and applied to the crystal for frequency correction.
DCXO
The following are key features of a DCXO:
- DCXO stands for Digitally Controlled Crystal Oscillator.
- It employs algorithms such as frequency estimation, correction, and tracking.
- It offers superior stability compared to VCXO and TCXO types.
- It is commonly used by GSM mobile phone manufacturers.
MCXO
The following are key features of an MCXO:
- MCXO stands for Microprocessor Compensated Crystal Oscillator.
- It utilizes a microprocessor to provide high processing capabilities for highly efficient compensation.
- An ADC (Analog-to-Digital Converter) is used alongside a DAC, replacing lookup tables.
- It delivers better performance but at a higher cost compared to other TCXO types.
