EXFO PSO-200 Optical Modulation Analyzer - Manual (Page 262)

Measurement Definitions
254 PSO-200
Measurements for Constellation Charts
Phase Error
The phase error (EP) describes the deviation of phase from the ideal
reference vector, illustrated in the graph. It is computed according to:
IQ Gain Imbalance
The gain imbalance describes the ratio between the I and Q part of the
signal and is computed according to:
The diagram below illustrates a signal with IQ gain imbalance and the
corresponding ideal reference vectors.
In-Phase Error
The in-phase error (EI) is the rms deviation of the I component of the error
vectors, denoted I in the graph. It is calculated according to:
given in percent to the magnitude of the longest reference vector.
EP
rms
1
N
----
I
meas
n ( )
Q
meas
n ( )
----------------------
 
 
atan
I
ref
r n ( )
Q
ref
r n ( )
------------
 
 
 
atan –
 
 
 
2
n 1 =
N 
deg   =
GI 20
1
N
----
I
meas
n ( ) I
ref
r n ( )

Q
meas
n ( ) Q
ref
r n ( )

--------------------------------------
 
 
 
2
n 1 =
N 
log dB   =
EI
rms
1
N
---- I
meas
n ( ) I
ref
r n ( )
–  
2
n 1 =
N 
100  %rms   =