MT-008 Datasheet, PDF (5/10 Pages) Analog Devices – Converting Oscillator Phase Noise to Time Jitter

MT-008
quantity 10 log₁₀[200 MHz – 0.01 MHz] to the phase noise in dBc/Hz. In practice, the lower
frequency limit of 0.01 MHz can be dropped from the calculation, as it does not affect the final
result significantly. A total rms jitter of approximately 1 ps is obtained using Eq. 3.
PHASE
NOISE
(dBc/Hz)
f_O = OSCILLATOR FREQUENCY (100MHz)
INTEGRATE TO ≈ 2 f_O = 200MHz
–150
A
10k
100k
1M
10M
100M
1G
f_{m FREQUENCY OFFSET (Hz)}
A = –150dBc + 10 log₁₀ 200×10⁶ – 0.01×10⁶ = –150dBc + 83dB = –67dBc
A/10
RMS PHASE JITTER (radians) ≈ 2•10
= 6.32×10^–4 radians
RMS JITTER (seconds) = ^{RMS PHASE JITTER (radians)} = 1ps
2 π f_O
Figure 5: Sample Jitter Calculation Assuming Broadband Phase Noise
Crystal oscillators generally offer the lowest possible phase noise and jitter, and some examples
are shown for comparison in Figure 6. All the oscillators shown have a typical 1/f corner
frequency of 20 kHz, and the phase noise therefore represents the white phase noise level. The
two Wenzel oscillators are fixed-frequency and represent excellent performance (Reference 9). It
is difficult to achieve this level of performance with variable frequency signal generators, as
shown by the –150 dBc specification for a relatively high quality generator.
‹ Wenzel ULN Series*
‹ Wenzel Sprinter Series,
–174dBc/Hz @ 10kHz+
–165dBc/Hz @ 10kHz+
‹ High Quality Signal Generator –150dBc/Hz @ 10kHz+
z Thermal noise floor of resistive source in a
matched system @ +25°C = –174dBm/Hz
z 0dBm = 1mW = 632mV p-p into 50Ω
z * An oscillator with an output of +13dBm (2.82V p-p) into 50Ω
with a phase noise of –174dBc/Hz has a noise floor of
+13dBm – 174dBc = –161dBm, 13dB above the thermal noise floor
(Wenzel ULN and Sprinter Series Specifications and
Pricing Used with Permission of Wenzel Associates)
Figure 6: 100-MHz Oscillator Broadband Phase Noise Floor Comparisons (Wenzel ULN
and Sprinter Series Specifications and Pricing used with Permission of Wenzel
Associates)
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