One thing that design engineers, buyers and supply chain specialists all share in common is the challenge of working within fast paced and deadline driven environments that demand projects, programs, and orders move forward. Understanding how to specify parts may appear straightforward to the casual observer, but for loyal customers and PRX Professionals that couldn't be further from the truth.
Unlike an ordinary voltage controlled oscillator (VCO), the crystal-controlled VCXO possesses the ability to accurately maintain a reference frequency, even in the event of a loss of the control signal and despite changes in the environment such as temperature or supply voltage. This characteristic is especially important in wireless applications where drop-outs can occur and is also of equal value for high-speed wire-line links such as ISDN, ATM and xDSL, where VCXOs maintain the essential frequency with minimal noise or jitter.
There are two most commonly used methods for specifying VCXO's. First, is the APR Method which specifies all performance operating conditions for the device. The second method is known as the Separate Method. The Separate Method specifies device performance under specific operating conditions and calls for defining separate operating parameters such as the frequency's deviation, stability, and tolerance over operating temperature range, output load, and supply voltage.
The APR Method uses the absolute pull range which allows the customer to simply specify one parameter. The Separate Method considers variations from nominal as the design engineer calculates the absolute pull range by starting with the total pull range of the VCXO, then subtracts the sum of all variations and tolerances such as calibration, temperature, power supply and load.
In conclusion, the APR Method is preferred because customers, buyers, and suppliers can easily calculate the requirements to the bottom line without concern toward individual factors.
