2-3
IM 704610-01E
Explanation of Functions
2
2.2
Measurement Principle
Example with Pulse Width Measurement
A time shorter than the period of the measurement clock is called the fractional time. In
general, since the measured signal and the measurement clock are not synchronized,
fractional time exists both at the beginning and at the end of measurements. This
instrument generates a “fractional pulse” which is a pulse signal equal to the sum of the
fractional time and one period of the measurement clock. Given pulse width T of the
measured signal, measurement clock period t
0
, and fractional pulse times T
a
and T
b
,
pulse width T can be divided into integer multiples of the measurement clock time N
times t
0
and fractional pulse times T
a
and T
b
as follows:
T = N • t
0
+ (T
a
– T
b
)
The instrument converts the fractional pulse times on the starting and ending sides (T
a
and T
b
) to voltage values. By then converting those voltages to digital values using 7-bit
A/D conversion, the fractional pulse widths can be measured at time resolutions of
approximately 100 ps per 1LSB. T is determined by substituting the measured fractional
pulse times with T
a
and T
b
in the equation above.
T
1
2
t0
N
Ta
Tb
Measured signal
Measurement clock
Fractional pulse
Time-voltage conversion
T = N · t
0
+ (T
a
– T
b
)
k: Coefficient used in the A/D conversion
A/D conversion
Fractional time
Fractional time
V = k · T
a
a
V = k · T
b
b
A/D conversion