The ∆% unit is used to measure a frequency as a percentage
difference from another frequency. It is calculated similarly to the %,
except that it uses the difference between the measured frequency and
the reference for the numerator:
where Fr is the reference frequency and F is the measured frequency.
Phase units
.
deg – Degrees, basic unit of phase
Degrees (abbreviated deg) is the basic unit of phase difference
between two signals. Phase is generally measured on a 360-degree
scale, where 0 degrees means the two signals are in phase, 180
degrees means they are out of phase, and by 360 degrees they are
back in phase. However, the scale may be shifted to span any
360-degree area, generally between –360 degrees and +360 degrees.
Digital Time Units
.
UI – Unit intervals, unit of time in digital signal
.
ppm – Parts per million; relative to a certain reference frequency
.
smp – Samples, unit of time in digital signal
There are several time units which are specific to digital signals.
Digital signals sometimes use normal time units such as Hertz or
seconds, but it is often more convenient to think of them in relation to
the digital signal itself. The UI unit is one such digital-specific signal.
One UI is the minimum amount of time between changes of state in a
digital signal. This unit of time can be calculated from the sample time
(the reciprocal of the sample rate), divided by the number of channels
(generally two), divided by the length of the sample frame (generally
32), divided again by two.
The ppm unit is used when comparing a frequency to a reference
frequency when the two are very close. It is similar to percent, but is
based on millions instead of hundreds. The formula for ppm is this:
where F is the measured frequency and Fr is the reference frequency.
Digital time may also be measured in samples. The time of each
sample is the reciprocal of the sample rate.
%=
F-Fr
Fr
100∆
PPM =
Fr
1,000,000
F-Fr
3 Operation
Units Operational Overview
3-32 ATS-1 Dual Domain User's Manual
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