LT5528
13
5528f
Application Measurements
The LT5528 is recommended for base-station applications
using various modulation formats. Figure 12 shows a typi-
cal application. The CAL box in Figure 12 allows for LO
feed-through and Image suppression calibration.
Figure 13 shows the ACPR performance for W-CDMA using
one, two or four channel modulation. Figures 14, 15 and 16
illustrate the 1-, 2- and 4-channel W-CDMA measurement.
To calculate ACPR, a correction is made for the spectrum
analyzer noise fl oor. If the output power is high, the ACPR
will be limited by the linearity performance of the part. If
the output power is low, the ACPR will be limited by the
noise performance of the part. In the middle, an optimum
ACPR is obtained.
Because of the LT5528’s very high dynamic-range, the
test equipment can limit the accuracy of the ACPR mea-
surement. Consult the factory for advice on the ACPR
measurement, if needed.
The ACPR performance is sensitive to the amplitude match
of the BBIP and BBIM (or BBQP and BBQM) inputs. This
is because a difference in AC current amplitude will give
rise to a difference in amplitude between the even-order
harmonic products generated in the internal V-I converter.
As a result, they will not cancel out entirely. Therefore, it
is important to keep the currents in those pins exactly the
same (but of opposite sign). The current will enter the
LT5528’s common-base stage, and will fl ow to the mixer
upper switches. This can be seen in Figure 1 where the
Figure 12. 1.5GHz to 2.4GHz Direct Conversion Transmitter Application with
LO Feed-Through and Image Calibration Loop
90°
0°
LT5528
BASEBAND
GENERATOR
CAL
LO FEED-THROUGH CAL OUT
IMAGE CAL OUT
PA
VCO/SYNTHESIZER
RF = 1.5GHz
TO 2.4GHz
EN
2, 4, 6, 9, 10, 12, 15, 17
5V
V-I
V-I
I-CHANNEL
Q-CHANNEL
BALUN
14
16
1
7
5
8, 13
V
CC
11
3
5528 F12
I-DAC
Q-DAC
ADC
Figure 14: 1-Channel W-CDMA Spectrum
RF FREQUENCY (MHz)
2127.5
POWER IN 30kHz BW (dBm)
5528 F14
2142.52137.52132.5 2147.5
2152.5
–30
–40
–60
–70
–80
–90
–120
–110
–100
–50
SYSTEM
NOISE FLOOR
CORRECTED
SPECTRUM
DOWNLINK TEST
MODEL 64 DPCH
UNCORRECTED
SPECTRUM
Figure 15: 2-Channel W-CDMA Spectrum
RF FREQUENCY (MHz)
2125
POWER IN 30kHz BW (dBm)
5528 F15
214021352130 2145
21552150
–30
–40
–60
–70
–80
–90
–120
–110
–100
–50
UNCOR-
RECTED
SPECTRUM
SYSTEM
NOISE FLOOR
CORRECTED
SPECTRUM
DOWNLINK TEST
MODEL 64
DPCH
Figure 13: W-CDMA APCR, AltCPR and Noise
vs RF Output Power at 2140MHz for 1, 2 and
4 Channels
RF OUTPUT POWER PER CARRIER (dBm)
–38–42
ACPR, AltCPR (dBc)
–55
–60
–65
–70
–75
–80
NOISE FLOOR AT 30MHz OFFSET (dBm/Hz)
–140
–150
–145
–155
–165
–160
5528 F13
–14–18–22–26–30–34
4-CH ACPR
2-CH ACPR
1-CH ACPR
4-CH AltCPR
2-CH AltCPR
DOWNLINK TEST MODEL 64 DPCH
1-CH AltCPR
4-CH NOISE
1-CH NOISE
Figure 16: 4-Channel W-CDMA Spectrum
DOWNLINK
TEST
MODEL 64
DPCH
RF FREQUENCY (MHz)
2115
POWER IN 30kHz BW (dBm)
5528 F16
214521352125 2155
2165
–40
–60
–70
–80
–90
–130
–120
–110
–100
–50
UNCOR-
RECTED
SPECTRUM
SYSTEM
NOISE FLOOR
CORRECTED SPECTRUM
CORRECTED
SPECTRUM
APPLICATIO S I FOR ATIO
WUU
U
