1-5
IM 704420-01E
Explanation of Functions
1
1.3
Measurement Functions (Measurement Items)
3T Jitter «See 4.1 for the operating procedure»
3T measurement
Measures the pulse width from the rising edge of the slope* to the next falling edge of
the slope (positive side) or from the falling edge of the slope to the next rising edge of
the slope (negative side) of the 3T data signal of a compact disk (CD).
*
Slope refers to the movement of the signal from a low level to a high level (rising edge) or
from a high level to a low level (falling edge).
Data
signal
Example of pulses on the positive side
Measurement
Measurement
Measurement
Measurement
×
N speed setting
You can set the
×
N speed of the drive being measured during 3T measurement. You
can select
×
1,
×
4, and
×
N (manual setting, where N is a value between 1.0 and 10.0).
Jitter
σ
, jitter ratio
σ
/T and average value
Determines a histogram (frequency distribution) from the measured values of multiple
pulses residing in the range from 2.5T to 3.5T (T = 231.385 ns), and calculates the
standard deviation
σ
from the histogram. This standard deviation
σ
is the 3T jitter.
The 3T jitter ratio is derived by dividing the standard deviation
σ
by the period of the
CD clock signal of 231.385 ns. The time-averaged value of the measured pulse width
signal is the average value AVE.
σ
=
Σ
(X
i
– AVE)
2
×
P
i
n
i = 1
n : Number of bins (histogram lines) of the histogram
X
i
: Class value of each bin
P
i
: Relative frequency
(Ratio of frequency Xi of a single bin with respect to
the total number of samples)
T : The period of the CD clock signal. When the speed is 1,
the period is 231.385 ns. When the speed is N, the
period is 231.385 ns/N.
• 3T jitter
AVE =
Σ
(X
i
×
P
i
)
n
i = 1
• 3T average value
• 3T jitter ratio
σ
T
×
100(%)
Note
You can also read statistics other than jitter, jitter ratio and average value by making inquiries
using communication commands. For details, see section 8.7.2, “CALCulation Group.”
