Preliminary
5-97
RF9678
Rev A4 010622
5
Adjusted Performance
In theory, an ideal quadrature modulator will completely suppress the carrier and sideband signals. In practice, due to
process and packaging effects, real quadrature modulators lack the balance necessary to completely cancel the carrier
and sideband signals. The imbalance caused by process and packaging effects is usually very small and may be cor-
rected by preadjusting the input signals to the modulator. This process of adjusting the input signals to minimize the car-
rier and sideband suppression is known as optimization.
Sideband suppression results from the summing together of the I and Q channel mixer outputs. In an ideal quadrature
modulator, at the summing point the sideband signals from the I and Q mixers are 180° out of phase and have equal
magnitudes. In a real modulator, the amplitude and phase are not exactly balanced and 100% cancellation does not
occur. The problem is corrected by introducing amplitude and phase corrections before applying a signal to the modula-
tor. Maximum sideband suppression is achieved when the amplitude and phase errors introduced by the modulator are
compensated for.
Complete carrier suppression occurs when there is no DC offset between the mixer signal input and the mixer reference
voltage (i.e., I SIG+ and I SIG-). In real devices, zero DC offset is difficult to achieve. This problem is corrected by intro-
ducing a DC offset of equal and opposite magnitude before applying the signal to the modulator. The internal error is
thereby canceled and maximum carrier suppression is achieved.
A
SWT
2 s
Unit
dBm
1RM
RBW
30 kHz
VBW
300 kHz
Ref Lvl
-3 dBm
Ref Lvl
-3 dBm
RF Att
20 dB
1.46848 MHz/
Center 380 MHz
Span 14.6848 MHz
EXT
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
1
Marker 1 [T1]
-21.97 dBm
380.01503006 MHz
1 [T1]
-21.97 dBm
380.01503006 MHz
CH PWR
-2.62 dBm
ACP Up
-50.30 dB
ACP Low
-49.72 dB
cu1
cu1
cl1
cl1
C0
C0
Date:
6.FEB.2001
00:47:49
Figure 4. W-CDMA Spectral Plot
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