AD9517-4/PCBZ Analog Devices Inc, AD9517-4/PCBZ Datasheet - Page 25

• Manufacturer Part Number: AD9517-4/PCBZ
• Description: BOARD EVALUATION AD9517-4
• Manufacturer: Analog Devices Inc

Specifications of AD9517-4/PCBZ

• Design Resources: High Performance, Dual Channel IF Sampling Receiver (CN0140)
• Main Purpose: Timing, Clock Generator
• Utilized Ic / Part: AD9517-4
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

TERMINOLOGY
Phase Jitter and Phase Noise
An ideal sine wave can be thought of as having a continuous
and even progression of phase with time from 0° to 360° for
each cycle. Actual signals, however, display a certain amount
of variation from ideal phase progression over time. This
phenomenon is called phase jitter. Although many causes can
contribute to phase jitter, one major cause is random noise,
which is characterized statistically as being Gaussian (normal)
in distribution.
This phase jitter leads to a spreading out of the energy of the
sine wave in the frequency domain, producing a continuous
power spectrum. This power spectrum is usually reported as
a series of values whose units are dBc/Hz at a given offset in
frequency from the sine wave (carrier). The value is a ratio
(expressed in dB) of the power contained within a 1 Hz
bandwidth with respect to the power at the carrier frequency.
For each measurement, the offset from the carrier frequency is
also given.
It is meaningful to integrate the total power contained within
some interval of offset frequencies (for example, 10 kHz to
10 MHz). This is called the integrated phase noise over that
frequency offset interval and can be readily related to the time
jitter due to the phase noise within that offset frequency interval.
Phase noise has a detrimental effect on the performance of
ADCs, DACs, and RF mixers. It lowers the achievable dynamic
range of the converters and mixers, although they are affected
in somewhat different ways.
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Time Jitter
Phase noise is a frequency domain phenomenon. In the time
domain, the same effect is exhibited as time jitter. When
observing a sine wave, the time of successive zero crossings
varies. In a square wave, the time jitter is a displacement of the
edges from their ideal (regular) times of occurrence. In both
cases, the variations in timing from the ideal are the time jitter.
Because these variations are random in nature, the time jitter is
specified in units of seconds root mean square (rms) or 1 sigma
of the Gaussian distribution.
Time jitter that occurs on a sampling clock for a DAC or an
ADC decreases the signal-to-noise ratio (SNR) and dynamic
range of the converter. A sampling clock with the lowest possible
jitter provides the highest performance from a given converter.
Additive Phase Noise
Additive phase noise is the amount of phase noise that is
attributable to the device or subsystem being measured. The
phase noise of any external oscillators or clock sources is
subtracted. This makes it possible to predict the degree to which
the device impacts the total system phase noise when used in
conjunction with the various oscillators and clock sources, each
of which contributes its own phase noise to the total. In many
cases, the phase noise of one element dominates the system
phase noise. When there are multiple contributors to phase
noise, the total is the square root of the sum of squares of the
individual contributors.
Additive Time Jitter
Additive time jitter is the amount of time jitter that is
attributable to the device or subsystem being measured. The
time jitter of any external oscillators or clock sources is subtracted.
This makes it possible to predict the degree to which the device
impacts the total system time jitter when used in conjunction with
the various oscillators and clock sources, each of which
contributes its own time jitter to the total. In many cases, the
time jitter of the external oscillators and clock sources dominates
the system time jitter.
AD9517-4