Anritsu BERTWave MP2100B, Руководство по эксплуатации, Страница: 44 / 382

Chapter 1 Outline
1-14
PRBS (Pseudo-Random Bit Sequence)
PRBS is the abbreviation for pseudorandom bit sequence. It is a bit string
approximating actual communications data with a random distribution of
“1” and “0”. In a bit length of 2
n
-1, n is called the number of the PRBS.
Using the BERTWave, n can be set to 7, 9, 15, 23, and 31.
Table 1.5-1 PRBS Bit Length
n 2
n
-1
7 127
9 511
15 32767
23 8388607
31 2147483647
The number of the PRBS used for measuring the Rx sensitivity is
determined by the communications standard.
RMS (root mean square)
This is the DC voltage consuming the equal power the same as the
consumed power when impressing AC voltage on a resistance.
In Voltage, RMS is DC voltage consuming the equal power when AC
voltage is impressing on a resistance.
R
R
V(t)
V
1
dt
R
t V
T
P
T


0
2
1
) ( 1
R
V
P
2
1
2
) (

0
V
t
0
V
t
V
1
Figure 1.5-2 AC and DC Voltage Power Consumption
In the circuit in Figure 1.5-2, the voltage V
1
when the power P
1
and P
2
consumed by resistance R is equal is the effective AC voltage V(t). V
1
is
the root mean square found using the following equation.


T
dt t V
T
V
0
2
1
) (
1
For a sine wave, the ratio of RMS and p-p is
2 2
.
Vrms means the effective voltage value.
Jitter rms is expressed as the standard deviation of the jitter time domain
histogram.