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Oscillation Circuit Evaluation Methods

What is "Frequency Deviation " (2) <Measurement Method>

As described in (What is "frequency deviation "(1) ＜Overview＞ ),Since Frequency deviation is derived by using the following equation, the object of measurement is F CL and F circuit.

 F nom ：Nominal frequency of the experimental crystal unit F CL※1 ：The frequency at a certain load capacitance (basically, the load capacitance specified in the specifications of the experimental crystal unit) of an experimental crystal unit (in most cases, a board-mounted crystal unit). F circuit※1 ：Frequency on the circuit when the experimental crystal unit is mounted on the circuit to be measured.

*1 : This symbol is not general (this is provided for convenience).

１．Measuring "F CL" method

＜Overview＞
Using network analyzer and CL jig, measure FCL according to the following procedure.(when the NDK crystal unit is mounted on the board(*2-).

(*1 2) If NDK crystal is not mounted on the board, an appropriate NDK crystal is prepared separately and used as the experimental crystal.

＜Measurement procedure＞

 （１） The crystal mounted on the board is removed with a soldering iron （２） After the crystal is cleaned (excess solder attached to the crystal is removed), waits until the crystal reaches normal room temperature. （３） Set the crystal in CL jig (the capacitance of the CL jig is basically the value specified in crystal specification sheet) （４） Set the CL jig in the network analyzer and measure the FCL of the crystal according to the manual of the network analyzer.

２．Measuring "F circuit " method

＜Overview＞
Mount the experimental crystal on the board, and measure the oscillation frequency under a specified temperature conditions according to the following measurement procedure.

＜Measurement procedure＞

 （１） Mount the experimental crystal unit on the board using a soldering iron. （２） After the crystal unit and its surrounding are stabilized at a specified temperature, the crystal unit is oscillated and its oscillation signal's data is acquired with non-contact method.(*2)using an antenna. （３） Amplify the oscillation signal spread by the antenna to the level that is stably measurable with frequency counter. （４） Measure F circuit with frequency counter.

(*2) If the oscillation frequency is measured by contacting voltage probe with the oscillation circuit, the capacitance of the voltage probe is added and the capacitance of the oscillation circuit changes, which affects oscillation frequency.
NDK uses non-contact method in order to measure the oscillation frequency as accurately as possible.

The measurement image of "F circuit" is shown below.

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