LT5568-2EUF-PBF LINER [Linear Technology], LT5568-2EUF-PBF Datasheet - Page 13

• Manufacturer Part Number: LT5568-2EUF-PBF
• Description: GSM/EDGE Optimized, High Linearity Direct Quadrature Modulator
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
Application Measurements
The LT5568-2 is recommended for base-station applica-
tions using various modulation formats. Figure 10 shows a
typical application. Figure 11 shows the ACPR performance
for CDMA2000 using 1- and 3-carrier modulation. Figures
12 and 13 illustrate the 1- and 3-carrier CDMA2000 RF
spectrum. 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 observed.
GENERATOR
BASEBAND
Q-DAC
I-DAC
EN
Figure 12. 1-Carrier CDMA2000 Spectrum
–100
–110
–120
–130
–30
–40
–50
–60
–70
–80
–90
Figure 10. 850MHz to 965MHz Direct
Conversion Transmitter Application
896.25
2, 4, 6, 9, 10, 12, 15, 17
UNCORRECTED
SPECTRUM
SPECTRUM ANALYSER NOISE FLOOR
14
16
1
7
5
897.75
U
Q-CHANNEL
V-I
V-I
I-CHANNEL
RF FREQUENCY (MHz)
899.25
U
90°
VCO/SYNTHESIZER
0°
900.75
V
DOWNLINK TEST
MODEL 64 DPCH
CC
W
CORRECTED
SPECTRUM
8, 13
3
902.25
BALUN
55682 F12
LT5568-2
903.75
55682 F10
U
11
100nF
x2
PA
5V
RF = 850MHz
TO 965MHz
Because of the LT5568-2’s very high dynamic range, the
test equipment can limit the accuracy of the ACPR mea-
surement. See Application Note 99. Consult the factory
for advice on the ACPR measurement, if needed.
The ACPR performance is sensitive to the amplitude match
of the BBPI and BBMI (or BBPQ and BBMQ) 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
–100
–110
–120
–130
Figure 13. 3-Carrier CDMA2000 Spectrum
–30
–40
–50
–60
–70
–80
–90
–50
–60
–70
–80
–90
894
–30
Figure 11. ACPR, AltCPR and Noise
CDMA2000 Modulation
UNCORRECTED
DOWNLINK TEST MODEL 64 DPCH
3-CH. NOISE
SPECTRUM
RF OUTPUT POWER PER CARRIER (dBm)
CORRECTED
SPECTRUM
896
–25
3-CH. ACPR
RF FREQUENCY (MHz)
898
–20
900
SPECTRUM ANALYSER
–15
NOISE FLOOR
902
3-CH. AltCPR
1-CH. AltCPR
DOWNLINK
1-CH. NOISE
MODEL 64
–10
DPCH
904
TEST
1-CH.
ACPR
LT5568-2
55682 F13
906
–5
55682 F11
–125
–145
–155
–165
–135
13
55682f