LT5528 LINER [Linear Technology], LT5528 Datasheet - Page 13

• Manufacturer Part Number: LT5528
• Description: 1.5GHz to 2.4GHz High Linearity Direct Quadrature Modulator
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
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.
Figure 14: 1-Channel W-CDMA Spectrum
–100
–110
–120
–30
–40
–50
–60
–70
–80
–90
Figure 12. 1.5GHz to 2.4GHz Direct Conversion Transmitter Application with
LO Feed-Through and Image Calibration Loop
GENERATOR
ADC
2127.5
BASEBAND
UNCORRECTED
SPECTRUM
Q-DAC
I-DAC
2132.5
EN
RF FREQUENCY (MHz)
2137.5
NOISE FLOOR
2, 4, 6, 9, 10, 12, 15, 17
SYSTEM
U
2142.5
14
16
1
7
5
DOWNLINK TEST
MODEL 64 DPCH
CORRECTED
SPECTRUM
V-I
Q-CHANNEL
V-I
I-CHANNEL
2147.5 2152.5
U
5528 F14
90°
VCO/SYNTHESIZER
0°
V
W
CC
8, 13
3
Figure 15: 2-Channel W-CDMA Spectrum
–100
–110
–120
BALUN
–30
–40
–50
–60
–70
–80
–90
2125
LT5528
DOWNLINK TEST
MODEL 64
DPCH
U
UNCOR-
RECTED
SPECTRUM
2130
11
CAL
RF FREQUENCY (MHz)
2135
NOISE FLOOR
LO FEED-THROUGH CAL OUT
IMAGE CAL OUT
SYSTEM
5V
PA
2140
RF = 1.5GHz
TO 2.4GHz
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
2145
5528 F12
CORRECTED
SPECTRUM
2150
5528 F15
2155
Figure 13: W-CDMA APCR, AltCPR and Noise
vs RF Output Power at 2140MHz for 1, 2 and
4 Channels
Figure 16: 4-Channel W-CDMA Spectrum
–55
–60
–65
–70
–75
–80
–100
–110
–120
–130
–42
–40
–50
–60
–70
–80
–90
4-CH NOISE
2115
RF OUTPUT POWER PER CARRIER (dBm)
DOWNLINK
TEST
MODEL 64
DPCH
CORRECTED SPECTRUM
–38
UNCOR-
RECTED
SPECTRUM
2-CH AltCPR
1-CH AltCPR
DOWNLINK TEST MODEL 64 DPCH
2125
–34
RF FREQUENCY (MHz)
–30
2135
NOISE FLOOR
4-CH ACPR
SYSTEM
1-CH NOISE
–26
4-CH AltCPR
2145
1-CH ACPR
–22
LT5528
2-CH ACPR
CORRECTED
SPECTRUM
–18
2155
5528 F13
13
–14
5528 F16
2165
–140
–145
–150
–155
–160
–165
5528f