303
Chapter 7 Tutorial
Signal Imperfections
4
7
Phase Noise Phase noise results from small, instantaneous changes in
the output frequency (“jitter”). It is seen as an elevation of the apparent
noise floor near the fundamental frequency and increases at 6 dBc / octave
with the carrier frequency. The 33250A’s phase noise specification
represents the sum of all noise components in a 30 kHz band centered on
the fundamental frequency. This “integrated phase noise” is related to
jitter by the following equation.
Jitter in Seconds (rms) = x
Quantization Errors Finite DAC resolution (12 bits) leads to voltage
quantization errors. Assuming the errors are uniformly distributed over
a range of ±0.5 least-significant bit (LSB), the equivalent noise level is
-74 dBc for a sine wave that uses the full DAC range (4,096 levels).
Similarly, finite-length waveform memory leads to phase quantization
errors. Treating these
errors as low-level phase modulation and assuming
a uniform distribution
over a range of ±0.5 LSB, the equivalent noise
level is -76 dBc for a sine wave that is 16K samples long. All of the
33250’s standard waveforms use the entire DAC range and are 16K
samples in length. Any arbitrary waveforms that use less than the
entire DAC range, or that are specified with fewer than 16,384 points,
will exhibit proportionally higher relative quantization errors.
1
2π Frequency×
---------------------------------------------10
Phase Noise in dBc / 20()
To Next Page
Loading...
Need help?
General
