LTC5598IUF LINER [Linear Technology], LTC5598IUF Datasheet - Page 13

• Manufacturer Part Number: LTC5598IUF
• Description: 5MHz to 1600MHz High Linearity Direct Quadrature Modulator
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
Table 7. RF Output Impedance vs Frequency for EN = High
The RF port output impedance for EN = Low is given in Table
8. It is roughly equivalent to a 1.3pF capacitor to ground.
Table 8. RF Output Impedance vs Frequency for EN = Low
In Figure 7 the simplifi ed circuit schematic of the RF
output buffer is drawn. A plot of the RF port return loss vs
frequency is drawn in Figure 8 for EN = High and Low.
Enable Interface
Figure 9 shows a simplifi ed schematic of the EN pin
interface. The voltage necessary to turn on the LTC5598
is 2V. To disable (shut down) the chip, the enable voltage
FREQUENCY
FREQUENCY
(MHz)
(MHz)
1000
1250
1500
1800
1000
1250
1500
1800
100
200
400
800
100
200
400
800
0.1
16
30
60
1
2
4
8
IMPEDANCE
IMPEDANCE
82.3 – j1223
RF OUTPUT
51.1 – j618
35.3 – j310
24.4 – j148
20.4 – j114
59.0 – j0.6
58.5 – j2.1
57.3 – j3.5
54.6 – j4.5
51.9 – j3.6
50.5 – j2.1
50.2 – j1.1
48.9 + j0.3
46.1 + j0.4
44.5 + j0.2
41.2 – j0.1
39.9 + j0.4
LO INPUT
14.7 – j68
13.1 – j54
50 – j0.5
50 – j0.2
49.7 + j0
42.8 + j0
17 – j87
REFLECTION COEFFICIENT
REFLECTION COEFFICIENT
0.083
0.081
0.076
0.061
0.040
0.022
0.011
0.005
0.002
0.003
0.011
0.041
0.058
0.077
0.097
0.113
0.995
0.987
0.965
0.906
0.878
0.847
0.818
0.785
MAG
MAG
ANGLE
–179.7
–179.4
ANGLE
–12.7
–23.6
–41.6
–60.8
–74.8
–86.5
–84.9
177.4
173.3
177.4
–18.1
–36.6
–46.4
–58.4
–70.7
–84.3
–3.6
–4.6
–9.2
–80
162
178
must be below 1V. If the EN pin is not connected, the chip
is enabled. This EN = High condition is assured by the 125k
on-chip pull-up resistor. It is important that the voltage at
the EN pin does not exceed V
Figure 7. Simplifi ed Circuit Schematic of the RF Output
EN
INTERNAL
INTERNAL
Figure 8. RF Port Return Loss vs Frequency
MIXERS
–40
–50
–60
FROM
–10
–20
–30
BIAS
0
1
125k
C6 = 220nF , SEE FIGURE 10
Figure 9: EN Pin Interface
50k
1k
10
1.8V
FREQUENCY (MHz)
1k
4.6V
EN = HIGH
2V
CC
V
CC2
1V
by more than 0.3V. Should
48Ω
48Ω
100
EN = LOW
V
5598 F07
CC1
3V
LTC5598
2.8V
INTERNAL
ENABLE
CIRCUIT
1000
5598 F08
RF
5598 F09
13
5598f