Glossary
Frequency Accuracy
Simple Clock oscillator or sine wave crystal oscillator without any means of reducing Crystal’s frequency vs. temperature character is a difference between specified center frequency and an oscillator’s output frequency (factory-shipped frequency) at 25°C. Freq.
Accuracy is specified when a user has no means of external frequency adjustment.
When frequency can be adjusted by using a trimmer capacitor or adjustable resistor from outside, you can make fine adjustments of the oscillator frequency to the center frequency.
In such cases, it is not necessary to specify the frequency accuracy in general, but adjustable range of frequency by a trimmer capacitor is specified instead.eristics.
Frequency Stability vs. Operating Temperature
It is frequency stability versus temperature.
When stability vs. temperature is specified:
Temperature stability ±10ppm max.
(25°C reference temp.),(operating) temp. range 0°C~70°C means that frequency is within ±10ppm over the operating temp. range with reference to the frequency at 25°C. When reference temp. is not specified:
Temperature stability ±10ppm, over operating temp. range 0°C~70°C means that output frequency is constantly within ±10ppm within the temp. range of 0°C~70°C.
Aging
Aging means the continuous change of frequency with the passage of time after removing all the elements that makes frequency unstable including variations in temp. and power, and load regulation.
Phase noise
Crystal oscillator produces undesirable phase noise near the output frequency.
With recent advancement of wide band communications system requires, high phase noise performance of Crystal oscillators is more and more required.
Phase noise is measured in the frequency domain, and is expressed as a ratio of signal power to noise power measured in a 1 Hz bandwidth at a given offset from the desired signal.
In NAKA’s VCXO, best close-in noise results have been obtained using fundamental AT cut Crystals in the range of 12 to 33MHz.
Generally higher frequency crystals result in higher close-in noise because of their lower Q and wider bandwidths but NAKA’s VCXO realizes good close-in phase noise performance in VCXO even at 100-130MHz, by using multiplication technique.
VCXO(VC-TCXO)
Frequency Deviation
Amount of frequency change which results from control voltage change.
Control Voltage
Varying voltage which is applied to the VCXO input terminal causing frequency change.
Polarity
Polarity is the direction of the change in the frequency relative to the change in control voltage.
For VCXO with positive polarity, as the control voltage is increased, the frequency becomes high. For VCXO with negative polarity, as the control voltage is increased, the frequency becomes low on the contrary
Linearity
Deviation from a best straight line relation of control voltage to output frequency change expressed in percent.
(ref to Linearity Specification MIL-55310C)