Q-Tech QT90 - Manual (Page 6)

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Q-TECH Corporation - 10150 W. Jefferson Boulevard, Culver City 90232 - Tel: 310-836-7900 - Fax: 310-836-2157 - www.q-tech.com
QT90 SERIES
HIGH-RELIABILITY MINIATURE CLOCK OSCILLATORS
1.8 to 5.0Vdc - 15kHz to 160MHz
Q-TECH
CORPORATION
QT9 0 (Revision H, January 2011) (ECO #10088)
Phase noise is measured in the frequency domain, and is expressed as a ratio of signal power to noise power measured in a 1Hz
bandwidth at an offset frequency from the carrier, e.g. 10Hz, 100Hz, 1kHz, 10kHz, 100kHz, etc. Phase noise measurement is made
with an Agilent E5052A Signal Source Analyzer (SSA) with built-in outstanding low-noise DC power supply source. The DC source
is floated from the ground and isolated from external noise to ensure accuracy and repeatability.
In order to determine the total noise power over a certain frequency range (bandwidth), the time domain must be analyzed in the
frequency domain, and then reconstructed in the time domain into an rms value with the unwanted frequencies excluded. This may be
done by converting L(f) back to Sφ(f) over the bandwidth of interest, integrating and performing some calculations.
The value of RMS jitter over the bandwidth of interest, e.g. 10kHz to 20MHz, 10Hz to 20MHz, represents 1 standard deviation of
phase jitter contributed by the noise in that defined bandwidth.
Figure below shows a typical Phase Noise/Phase jitter of a QT90L, 3.3Vdc, 20MHz clock at offset frequencies 10Hz to 5MHz, and
phase jitter integrated over the bandwidth of 12kHz to 1MHz.
Phase Noise and Phase Jitter Integration
Period Jitter
As data rates increase, effects of jitter become critical with its
budgets tighter. Jitter is the deviation of a timing event of a
signal from its ideal position. Jitter is complex and is
composed of both random and deterministic jitter
components. Random jitter (RJ) is theoretically unbounded
and Gaussian in distribution. Deterministic jitter (DJ) is
bounded and does not follow any predictable distribution.
DJ is also referred to as systematic jitter. A technique to
measure period jitter (RMS) one standard deviation (1σ) and
peak-to-peak jitter in time domain is to use a high sampling
rate (>8G samples/s) digitizing oscilloscope. Figure shows
an example of peak-to-peak jitter and RMS jitter (1σ) of a
QT90L-100MHz, at 3.3Vdc.
RMS jitter (1σ): 7.7ps Peak-to-peak jitter: 56ps
Symbol Definition
∫ L(f) Integrated single side band phase noise (dBc)
Sφ (f)=(180/Π)x √ 2 ∫ L(f)df Spectral density of phase modulation, also known as RMS phase error (in degrees)
RMS jitter = Sφ (f)/(fosc.360°) Jitter(in seconds) due to phase noise. Note Sφ (f) in degrees.