lt5572 Linear Technology Corporation, lt5572 Datasheet - Page 13

• Manufacturer Part Number: lt5572
• Description: 1.5ghz To 2.5ghz High Linearity Direct Quadrature Modulator
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
Application Measurements
The LT5572 is recommended for basestation applications
using various modulation formats. Figure 10 shows a typical
application. Figure 11 shows the ACPR performance for
W-CDMA using 1-, 2- or 4-channel modulation. Figures
12, 13 and 14 illustrate the 1-, 2- and 4-channel W-CDMA
Figure 12. 1-Channel W-CDMA Spectrum
–100
–120
–110
GENERATOR
–60
–70
–80
BASEBAND
–30
–40
–50
–90
Q-DAC
Figure 10. 1.5GHz to 2.4GHz Direct Conversion Transmitter Application
2.1275
I-DAC
UNCORRECTED
DOWNLINK TEST
MODEL 64 DPCH
NOISE FLOOR
SPECTRUM
SPECTRUM
EN
ANALYSER
2.1325
2, 4, 6, 9, 10, 12, 15, 17
RF FREQUENCY (GHz)
2.1375
14
16
1
7
5
U
2.1425
V-I
V-I
Q-CH
I-CH
CORRECTED
SPECTRUM
U
2.1475 2.1525
5572 F12
90°
VCO/SYNTHESIZER
0°
W
V
CC
8, 13
3
Figure 13. 2-Channel W-CDMA Spectrum
–100
–110
–120
–70
–80
–30
–40
–50
–60
–90
BALUN
2.125
DOWNLINK
TEST MODEL
64 DPCH
SPECTRUM
LT5572
ANALYSER
U
2.13
FLOOR
NOISE
UNCORRECTED SPECTRUM
11
5572 TA01a
RF FREQUENCY (GHz)
2.135
100nF
×2
2.14
PA
measurement. To calculate ACPR, a correction is made for
the spectrum analyzer noise fl oor (Application Note 99).
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.
RF = 1.5GHz
5V
TO 2.5GHz
2.145
CORRECTED
SPECTRUM
2.15
Figure 11. W-CDMA ACPR, ALTCPR and Noise vs RF
Output Power at 2140MHz for 1, 2 and 4 Channels
5572 F13
2.155
–50
–70
–80
–90
–60
–30
DOWNLINK TEST
MODEL 64 DPCH
2-CH AltCPR
RF OUTPUT POWER PER CARRIER (dBm)
–100
–110
–120
Figure 14. 4-Channel W-CDMA Spectrum
–30
–40
–50
–60
–70
–80
–90
4-CH NOISE
–25
2-CH ACPR
2.115
4-CH AltCPR
DOWNLINK TEST
MODEL 64
DPCH
SPECTRUM
ANALYSER
4-CH ACPR
–20
FLOOR
NOISE
2.125
UNCORRECTED SPECTRUM
2-CH NOISE
RF FREQUENCY (GHz)
–15
2.135
1-CH AltCPR
1-CH NOISE
–10
2.145
5572 TA01b
LT5572
ACPR
1-CH
CORRECTED
SPECTRUM
–5
2.155
–125
–145
–155
–165
–135
13
5572 F14
2.165
5572f