lt5572 Linear Technology Corporation, lt5572 Datasheet - Page 11

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

APPLICATIO S I FOR ATIO
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)
(MHz)
1000
1400
1600
1800
2000
2200
2400
2600
1000
1400
1600
1800
2000
2200
2400
2600
1000
1400
1600
1800
2000
2200
2400
2600
= 0dBm
= 0dBm
22
OUTPUT IMPEDANCE
INPUT IMPEDANCE
OUTPUT IMPEDANCE
with no LO power applied is given in
U
32.2+j20.3
44.9+j21.8
56.4+j12.2
32.9+j11.0
51.2+j45.6
97.8-j65.8
58.6-j67.8
39.0-j55.6
29.6-j43.2
23.7-j30.8
19.7-j20.5
133-j11.8
20.7+j9.9
52.6+j0.5
43.0+j0.5
36.8+j5.6
21.2+j10.1
35.3+j18.4
46.1+j14.1
34.8+j11.8
32.8+j16.1
47.4+j5.0
42.0+j3.0
37.5+j6.8
(Ω)
(Ω)
(Ω)
U
W
0.409
0.456
0.502
0.534
0.540
0.527
0.506
0.503
0.434
0.319
0.230
0.129
0.025
0.075
0.164
0.243
Mag
Mag
0.424
0.270
0.150
0.057
0.093
0.162
0.224
0.279
Mag
S
S
S
11
22
22
U
Angle
Angle
–108
–130
–4.5
Angle
–30
–51
–69
–87
153
117
176
153
140
64
90
56
10
153
117
114
157
147
134
126
97
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 linearity performance if the 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 for 1dB compression
measurements.
Enable Interface
Figure 6 shows a simplifi ed schematic of the EN pin
interface. The voltage necessary to turn on the LT5572
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 75k on-chip pull-down resistor. It is important
that the voltage at the EN pin does not exceed V
more than 0.5V. If this should occur, the full-chip supply
FREQUENCY
Figure 5. Equivalent Circuit Schematic of the RF Output
(MHz)
1000
1400
1600
1800
2000
2200
2400
2600
22
52.5
for lower frequencies, a shunt capacitor
OUTPUT IMPEDANCE
22
30.6+j20.2
41.8+j23.6
55.6+j18.5
58.3+j49.1
20.3+j9.7
40.4+j3.1
34.7+j8.3
is given in Table 6.
48.8-j0.1
2.1pF
(Ω)
3nH
20pF
22
V
CC
. Figure 5 shows the
5572 F05
RF
OUTPUT
0.440
0.338
0.264
0.181
0.089
0.012
0.112
0.205
Mag
LT5572
S
22
11
Angle
-172
154
120
160
146
95
63
28
CC
5572f
by