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PDF LT5571 Data sheet ( Hoja de datos )
| Número de pieza | LT5571 | |
| Descripción | 620MHz - 1100MHz High Linearity Direct Quadrature Modulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
■ Direct Conversion from Baseband to RF
■ High Output: –4.2dB Conversion Gain
■ High OIP3: 21.7dBm at 900MHz
■ Low Output Noise Floor at 20MHz Offset:
No RF: –159dBm/Hz
POUT = 4dBm: –153.3dBm/Hz
■ Low Carrier Leakage: –42dBm at 900MHz
■ High Image Rejection: –53dBc at 900MHz
■ 3-Ch CDMA2000 ACPR: –70.4dBc at 900MHz
■ Integrated LO Buffer and LO Quadrature Phase
Generator
■ 50Ω AC-Coupled Single-Ended LO and RF Ports
■ High Impedance DC Interface to Baseband Inputs
with 0.5V Common Mode Voltage
■ 16-Lead QFN 4mm × 4mm Package
APPLICATIONS
■ RFID Interrogators
■ GSM, CDMA, CDMA2000 Transmitters
■ Point-to-Point Wireless Infrastructure Tx
■ Image Reject Up-Converters for Cellular Bands
■ Low-Noise Variable Phase-Shifter for 620MHz to
1100MHz Local Oscillator Signals
LT5571
620MHz – 1100MHz High
Linearity Direct Quadrature
Modulator
DESCRIPTION
The LT®5571 is a direct I/Q modulator designed for high
performance wireless applications, including wireless
infrastructure. It allows direct modulation of an RF signal
using differential baseband I and Q signals. It supports
RFID, GSM, EDGE, CDMA, CDMA2000, and other systems.
It may also be configured as an image reject upconvert-
ing mixer by applying 90° phase-shifted signals to the I
and Q inputs. The high impedance I/Q baseband inputs
consist of voltage-to-current converters that in turn drive
double-balanced mixers. The outputs of these mixers are
summed and applied to an on-chip RF transformer, which
converts the differential mixer signals to a 50Ω single-
ended output. The four balanced I and Q baseband input
ports are intended for DC-coupling from a source with a
common-mode voltage at about 0.5V. The LO path consists
of an LO buffer with single-ended input, and precision
quadrature generators that produce the LO drive for the
mixers. The supply voltage range is 4.5V to 5.25V.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
Direct Conversion Transmitter Application
I-DAC
EN
Q-DAC
V-I
I-CH
Q-CH
V-I
VCC LT5571
0°
90°
BALUN
5V
100nF
×2 RF = 620MHz
TO 1100MHz
PA
BASEBAND
GENERATOR
VCO/SYNTHESIZER
5571 TA01a
CDMA2000 ACPR, AltCPR and Noise vs RF
Output Power at 900MHz for 1 and 3 Carriers
–40
DOWNLINK TEST
MODEL 64 DPCH
–110
–50
3-CH ACPR
–120
–60 3-CH AltCPR
1-CH
ACPR –130
–70 –140
–80 1-CH AltCPR
1-CH NOISE
–150
3-CH NOISE
–90
–30 –25 –20 –15 –10 –5
–160
0
RF OUTPUT POWER PER CARRIER (dBm)
5571 TA01b
5571f
1
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LT5571
TYPICAL PERFORMANCE CHARACTERISTICS VCC = 5V, EN = High, TA = 25°C, fLO = 900MHz,
fRF = 902MHz, PLO = 0dBm. BBPI, BBMI, BBPQ, BBMQ CM input voltage = 0.5VDC, Baseband Input Frequency fBB = 2MHz, I & Q 90°
shifted, without image or LO feedthrough nulling. fRF = fBB + fLO (upper sideband selection). PRF(OUT) = –10dBm (–10dBm/tone for 2-
tone measurements), unless otherwise noted. (Note 3)
Noise Floor vs RF Frequency
–157
fLO = 900MHz (FIXED)
NO BASEBAND SIGNAL
–158
–159
–160
5V, –40°C
5V, 25°C
–161
5V, 85°C
4.5V, 25°C
5.5V, 25°C
–162
550 650 750 850 950 1050 1150 1250
RF FREQUENCY (MHz)
5571 G10
Absolute I/Q Gain Imbalance vs
LO Frequency
0.3
5V, –40°C
5V, 25°C
5V, 85°C
4.5V, 25°C
0.2 5.5V, 25°C
0.1
0
550 650 750 850 950 1050 1150 1250
LO FREQUENCY (MHz)
5571 G13
Output IP3 vs LO Power
24
22
20
18 5V, –40°C
5V, 25°C
16 5V, 85°C
4.5V, 25°C
14 5.5V, 25°C
12
10
–20 –16 –12 –8 –4
fBB, 1 = 2MHz
fBB, 2 = 2.1MHz
048
LO INPUT POWER (dBm)
5571 G16
Image Rejection vs LO Frequency
–30
5V, –40°C
5V, 25°C
–35 5V, 85°C
4.5V, 25°C
5.5V, 25°C
–40
–45
–50
–55
550 650 750 850 950 1050 1150 1250
LO FREQUENCY (MHz)
5571 G11
Absolute I/Q Phase Imbalance vs
LO Frequency
3
5V, –40°C
5V, 25°C
5V, 85°C
4.5V, 25°C
2 5.5V, 25°C
1
0
550 650 750 850 950 1050 1150 1250
LO FREQUENCY (MHz)
5571 G14
LO Feedthrough vs LO Power
–38
–40
–42
–44
–46
–48
–50
–20 –16 –12 –8 –4
5V, –40°C
5V, 25°C
5V, 85°C
4.5V, 25°C
5.5V, 25°C
048
LO INPUT POWER (dBm)
5571 G17
LO and RF Port Return Loss vs
Frequency
0
LO PORT, EN = LOW
LO PORT, EN = HIGH, PLO = 0dBm
–10
–20
RF PORT,
EN = LOW
–30
RF PORT,
EN = HIGH,
NO LO
–40
550 650 750
RF PORT,
EN = HIGH,
PLO = 0dBm
LO PORT,
EN = HIGH,
PLO = –10dBm
850 950 1050 1150 1250
FREQUENCY (MHz)
5571 G12
Voltage Gain vs LO Power
–2
–4
–6
–8
–10
–12
–14
–16
–18
–20
–20 –16 –12 –8 –4
5V, –40°C
5V, 25°C
5V, 85°C
4.5V, 25°C
5.5V, 25°C
048
LO INPUT POWER (dBm)
5571 G15
Image Rejection vs LO Power
–35
–40
–45
–50
–55
–60
–20
5V, –40°C
5V, 25°C
5V, 85°C
4.5V, 25°C
5.5V, 25°C
–16 –12 –8 –4 0 4
LO INPUT POWER (dBm)
8
5571 G18
5571f
5
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LT5571
APPLICATIONS INFORMATION
Table 3. LO Port Input Impedance vs Frequency for EN = Low
and PLO = 0dBm
FREQUENCY INPUT IMPEDANCE
S11
(MHz)
(Ω) Mag Angle
500
35.6 + j42.1
0.467
83
600
65.5 + j70.1
0.531
46
700
163 + j76.3
0.602
14
800
188 – j95.2
0.654
–13
900
72.9 – j114
0.692
–36
1000
34.3 – j83.5
0.715
–56
1100
21.6 – j63.3
0.726
–73
1200
16.4 – j50.5
0.727
–86
For EN = Low the S22 is given in Table 6.
Table 6. RF Port Output Impedance vs Frequency for EN = Low
FREQUENCY
(MHz)
OUTPUT IMPEDANCE
(Ω)
S22
Mag Angle
500
21.5 + j5.0
0.403
166
600
26.9 + j11.8
0.333
144
700
36.5 + j16.0
0.239
120
800
48.8 + j11.2
0.113
89
900
52.8 – j2.2
0.035
–38
1000
46.6 – j11.5
0.123
–99
1100
39.7 – j13.9
0.191
–117
1200
35.0 – j13.0
0.232
–130
RF Section
After up-conversion, the RF outputs of the I and Q mixers are
combined. An on-chip balun performs internal differential
to single-ended output conversion, while transforming the
output signal impedance to 50Ω. Table 4 shows the RF
port output impedance vs frequency.
Table 4. RF Port Output Impedance vs Frequency for EN = High
and PLO = 0dBm
FREQUENCY OUTPUT IMPEDANCE
S22
(MHz)
(Ω) Mag Angle
500
22.2 + j5.2
0.390
165
600
28.4 + j11.7
0.311
143
700
38.8 + j14.3
0.202
119
800
49.4 + j6.8
0.068
91
900
49.4 – j5.8
0.058
–92
1000
42.7 – j11.7
0.149
–115
1100
36.9 – j12.6
0.207
–128
1200
33.2 – j11.3
0.241
–138
The RF output S22 with no LO power applied is given in
Table 5.
Table 5. RF Port Output Impedance vs Frequency for EN = High
and No LO Power Applied
FREQUENCY
(MHz)
OUTPUT IMPEDANCE
(Ω)
S22
Mag Angle
500
22.9 + j5.3
0.377
165
600
30.0 + j11.2
0.283
143
700
40.6 + j11.2
0.160
123
800
47.3 + j1.9
0.034
145
900
44.2 – j7.4
0.099
–123
1000
38.4 – j10.4
0.175
–131
1100
34.2 – j10.2
0.221
–140
1200
31.7 – j8.7
0.246
–148
To improve S22 for lower frequencies, a series capacitor
can be added to the RF output. At higher frequencies, a
shunt inductor can improve the S22. Figure 5 shows the
equivalent circuit schematic of the RF output.
Note that an ESD diode is connected internally from the
RF output to ground. For strong output RF signal levels
(higher than 3dBm) this ESD diode can degrade the lin-
earity performance if an external 50Ω termination imped-
ance is connected directly to ground. To prevent this, a
coupling capacitor can be inserted in the RF output line.
This is strongly recommended during 1dB compression
measurements.
47Ω
VCC
21pF
RF
OUTPUT
1pF 7nH
5571 F05
Figure 5. Equivalent Circuit Schematic of the RF Output
Enable Interface
Figure 6 shows a simplified schematic of the EN pin inter-
face. The voltage necessary to turn on the LT5571 is 1V.
To disable (shut down) the chip, the enable voltage must
be below 0.5V. If the EN pin is not connected, the chip is
disabled. This EN = Low condition is guaranteed by the
75kΩ on-chip pull-down resistor.
It is important that the voltage at the EN pin does not
exceed VCC by more than 0.5V. If this should occur, the
5571f
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LT5571.PDF ] | |
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