3
Introduction and Standards
Precision Oscillators / Frequency Control Devices
The following material briefly describes our in-house
standards and offers some cost/performance tradeoffs.
ENVIRONMENTAL CONDITIONS
See Page 1.
FREQUENCY RANGE
From less than 1Hz to 1GHz, Murata Electronics designs
typically center around the “AT” cut crystals,
but “SC,” “IT,” and other cuts are used for certain
applications. Fundamental mode crystals from 3MHz
and overtones from 5 to 400MHz are utilized in the
oscillators. This range is extended through the use of
dividers and multipliers. (Oscillators in the microwave
range are available through the Murata RF and
Microwave Products Group in State College,
Pennsylvania.)
FREQUENCY STABILITY
ls generally defined in two ways:
1.0 Total Frequency Stability – the maximum frequency
excursion from the nominal for all conditions. This is
usually expressed as a ± fraction centered at the
nominal frequency.
FREQUENCY STABILITY [ppm] f[Hz]
2.0 Specific Stabilities – fc[MHz]
2.1 Accuracy – the frequency setting tolerance at
room temperature at time of shipment.
Oscillators may incorporate external
adjustments for exact calibration. TCXO’s
typically exhibit a resolution of ±1pp 107. For
OCXO’s, the typical resolution is to ±1pp109.
2.2 Frequency Stability Versus Temperature – a
maximum change from the nominal frequency.
Oscillators relying on the temperature
characteristics of the “AT” crystal can be
designed to meet a stability requirement as
tight as ±10ppm from –10°C to +60°C. Tighter
stabilities to ±0.1ppm require temperature
compensation techniques. Ovenized oscillators
are used for stabilities to ±5pp 1010.
2.3 Frequency Stabilities Versus Supply Voltage
and Load Variation – these parameters may be
improved by the use of voltage regulation and
additional buffer stages. The tighter the stability
requirements, the more complex
the design.
2.4 Stability Versus Time – can be expressed over
periods of milliseconds to years. Through use
of high quality crystals typical aging rates of
±1ppm/year are achieved. For OCXO’s, it is
possible to achieve aging rates as low as
±5pp 1010 per day. Short term stability can be
expressed as an Allan Variance over a range
of gate times from less than 1msec to 10sec,
or in terms of SSB phase noise in the frequency
domain.
OUTPUT CHARACTERISTICS
Oscillator output waveforms are either sine or square
waves.
1.0 Sine Waves – outputs are specified by stating the
amplitude of the signal (mW or VRMS and the
nominal load impedance (typically) 50 ohms or
1K ohms).
Harmonic and Sub-Harmonic distortion less than –20dBc
is standard.
Deviations from the standards can be accommodated.
Consult our engineering department.
2.0 Square Wave*
TTL CMOS ECL
Logic “0” Level 0.4V Max. 1.0V Max. –1.89V
Logic “1” Level 2.4V Min. Vcc –1.0V –0.89
Symmetry 40/60 40/60 40/60
50 ohms
Load 10 Gates 50pF Max. to –2VDC
1Hz to 1Hz to 4.0MHz to
Freq. Range 100MHz 100MHz 700MHz
*Specify logic type to be driven
RELATIVE FREQUENCY STABILITY OF TYPICA L
CRYSTAL OSCILLATOR TYPES
+10ppm–
0–
–10ppm–
f/f
–40°C +20°C +80°C
Temperature
Uncompensated
“AT” Cut
Crystal Osc.
(XO)
Ovenized Crystal Oscillator
(OCXO) Analog Temp.
Compensation
(TCXO)