R&S SMJ100A, Operating Manual

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Instrument Function
R&S
®
SMJ100A
290 Operating Manual 1403.7458.32 ─ 14
Figure 5-14: Negative gain imbalance (left) and positive gain imbalance (right) in the I/Q constellation
diagram
5.7.1.2 I and Q Offset
An I offset adds a constant value to all I amplitudes, leaving the Q amplitudes
unchanged. A Q offset has the opposite effect. A combination of I and Q values results
in an I/Q offset, which is due to carrier feedthrough in the I/Q modulator. Possible rea-
sons are interfering signals at the RF carrier frequency, e.g. an unsuppressed RF car-
rier subchannel. The effect of a positive I and Q offset in the I/Q constellation diagram
is shown on
Figure 5-15 .
Figure 5-15: I offset (left) and Q offset (right) in the I/Q constellation diagram
5.7.1.3 Quadrature Offset
Changes the phase angle between the I and the Q vectors from the ideal 90 degrees,
while the amplitudes are maintained. A positive quadrature offset results in a phase
angle greater than 90 degrees. The effect of a positive quadrature offset in the I/Q con-
stellation diagram is shown on
Figure 5-16 .
Impairment of Digital I/Q Signal and Noise Generator - AWGN/IMP Block