Q-Tech QT50 - 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
DUAL IN-LINE PACKAGES
CRYSTAL CLOCK OSCILLATORS
-5.2 to -4.5Vdc & 1.8 to 15Vdc - 0.01Hz to 200MHz
Dual In-line Packages (Revision G, August 2011 ) (ECO# 10297)
Q-TECH
CORPORATION
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 QT6AC8, 5.0Vdc, 24MHz and a QT50T, 5.0Vdc, 60 MHz 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 QT6AC8-
24MHz, at 5.0Vdc.
RMS jitter (1σ): 5.86ps Peak-to-peak jitter: 52.4ps
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.
QT6AC8, 5.0Vdc, 24MHz QT50T, 5.0Vdc, 60 MHz