lt5571 Linear Technology Corporation, lt5571 Datasheet - Page 11

• Manufacturer Part Number: lt5571
• Description: 620mhz - 1100mhz High Linearity Direct Quadrature Modulator
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
Table 3. LO Port Input Impedance vs Frequency for EN = Low
and P
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 P
The RF output S
Table 5.
Table 5. RF Port Output Impedance vs Frequency for EN = High
and No LO Power Applied
FREQUENCY
FREQUENCY
FREQUENCY
LO
LO
(MHz)
(MHz)
1000
1100
1200
1000
1100
1200
(MHz)
500
600
700
800
900
1000
1100
1200
500
600
700
800
900
500
600
700
800
900
= 0dBm
= 0dBm
22
OUTPUT IMPEDANCE
INPUT IMPEDANCE
OUTPUT IMPEDANCE
with no LO power applied is given in
28.4 + j11.7
38.8 + j14.3
42.7 – j11.7
36.9 – j12.6
33.2 – j11.3
35.6 + j42.1
65.5 + j70.1
34.3 – j83.5
21.6 – j63.3
16.4 – j50.5
163 + j76.3
188 – j95.2
72.9 – j114
22.2 + j5.2
49.4 + j6.8
49.4 – j5.8
30.0 + j11.2
40.6 + j11.2
38.4 – j10.4
34.2 – j10.2
22.9 + j5.3
47.3 + j1.9
44.2 – j7.4
31.7 – j8.7
(Ω)
(Ω)
(Ω)
0.467
0.531
0.602
0.654
0.692
0.715
0.726
0.727
0.390
0.311
0.202
0.068
0.058
0.149
0.207
0.241
Mag
Mag
0.377
0.283
0.160
0.034
0.099
0.175
0.221
0.246
Mag
S
S
S
11
22
22
Angle
Angle
–115
–128
–138
Angle
–13
–36
–56
–73
–86
165
143
119
–92
–123
–131
–140
–148
83
46
14
91
165
143
123
145
For EN = Low the S
Table 6. RF Port Output Impedance vs Frequency for EN = Low
To improve S
can be added to the RF output. At higher frequencies, a
shunt inductor can improve the S
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.
Enable Interface
Figure 6 shows a simplifi ed 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 V
FREQUENCY
Figure 5. Equivalent Circuit Schematic of the RF Output
(MHz)
1000
1100
1200
500
600
700
800
900
CC
by more than 0.5V. If this should occur, the
22
47Ω
for lower frequencies, a series capacitor
OUTPUT IMPEDANCE
22
26.9 + j11.8
36.5 + j16.0
48.8 + j11.2
46.6 – j11.5
39.7 – j13.9
35.0 – j13.0
21.5 + j5.0
52.8 – j2.2
is given in Table 6.
1pF
(Ω)
7nH
21pF
22
V
CC
. Figure 5 shows the
5571 F05
RF
OUTPUT
0.403
0.333
0.239
0.113
0.035
0.123
0.191
0.232
Mag
LT5571
S
22
11
Angle
–117
–130
166
144
120
–38
–99
89
5571f