1-2
IM 704210-01E
1.2 Measuring Principles and Sampling Mode
Measuring Principles
Time shorter than the period of the reference clock is called fractional time. In general, since the
signal to be measured is not synchronized with the reference clock, fractional time exists at both
beginning and end of measurement. This instrument generates a fractional pulse comprised of the
fractional time and the time equivalent to one cycle of the reference clock.
With the pulse width of the signal to be measured, period of the reference clock and time span of
each fractional pulse assumed to be T, t
0
, Ta and Tb respectively, T can be separated into
multiplication of the period of the reference clock (N • t
0
) and period of each fractional pulse (T
a
and T
b
) as shown below.
T = N • t
0
+ (T
a
– T
b
)
With this instrument, T
a
and T
b
, the time of fractional pulses generated at the beginning and end
of measurement, are converted into a voltage value, which is then converted into a digital value
by a 8-bit A/D converter. This enables measurement of the time of fractional pulse, with time
resolution of 100 ps per 1 LSB. T is calculated by substituting the measured time of each
fractional pulse for T
a
and T
b
of the above formula.
T
1
2
t0
N
Ta
Tb
V =k·T
V =k·T
Signal to be measured
Reference clock
Fractional pulse
Time-voltage conversion
a
a
b b
T =N·t + (T –T )
k: A/D conversion factor
b
a
0
A/D conversion
A/D conversion
Sampling Mode
≡
For operating procedure, refer to 5.1
≡
Two sampling modes are available: time stamp mode and hardware histogram mode. The
sampling method (acquisition method of measured data) and display format (display method)
differ depending on the sampling mode. For a detailed description of display format, refer to 1.6,
“Displaying the Measured/Computed Data”.
Time stamp mode
Measured values and their time stamps (i.e. the time on which measurement is taken) are acquired
into the acquisition memory, and used as time-series data. The maximum sample size (i.e. the
maximum allowable number of data items to be acquired) is 32,000, though it varies depending
on the measurement function (refer to section 1.3). The measured values can be displayed in four
formats (histogram, list (measured values and time stamp), time variation and statistic values.
* Time stamp is expressed as the elapsed time between that when arming is activated (refer to
section 1.5) and when measurement for one sample is completed.
Hardware histogram mode
The measured value and its occurrence frequency are acquired into the acquisition memory. The
maximum sample size (i.e. the maximum allowable number of data items to be acquired) is
99,999,999. The measured values can be displayed in three formats (histogram, list (measured
values and frequency) and statistic values.).
