LTC5598IUF LINER [Linear Technology], LTC5598IUF Datasheet - Page 12

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

LTC5598
The LOP port return loss for the low end of the operating
frequency range can be optimized using extra 120Ω
terminations at the LO inputs (replace C9 and C10 with 120Ω
resistors, see Figure 10), and is shown in Figure 5.
The LOP port return loss for the high end of the operating
frequency range can be optimized using slightly different
values for C9, C10 and L1, L2 (see Figure 6).
The third-harmonic rejection on the applied LO signal is
recommended to be equal or better than the desired image
rejection performance since third-harmonic LO content can
degrade the image rejection severely. Image rejection is
not sensitive to second-harmonic LO content.
APPLICATIONS INFORMATION
12
Figure 5. LO Port Return Loss vs Frequency
Optimized for Low Frequency (See Figure 10)
Figure 6. LO Port Return Loss vs Frequency
Optimized for High Frequency (See Figure 10)
–10
–12
–14
–10
–30
–40
–20
–6
–4
–5
0
1000
1
C9, C10: 120Ω; L1, L2: 0Ω; C5, C7: 100nF
C9, C10: 2.7pF; L1, L2: 1.5nH; C5, C7: 10nF
EN = HIGH; P
EN = LOW; P
EN = LOW; P
1200
10
FREQUENCY (MHz)
FREQUENCY (MHz)
LO
LO
EN = LOW
1400
= 0dBm
= 0dBm
LO
EN = HIGH; P
= 10dBm
EN = HIGH
1600
100
LO
1800
= 10dBm
1000
5598 F05
5598 F06
2000
The large-signal noise fi gure can be improved with a
higher LO input power. However, if the LO input power is
too large and causes internal clipping in the phase shifter
section, the image rejection can be degraded rapidly. This
clipping point depends on the supply voltage, LO frequency,
temperature and single-ended vs differential LO drive. At
f
drive, this clipping point is at about 16.6dBm. For 4.5V it
lowers to 14.6dBm. For differential drive with V
is about 20dBm.
The differential LO port input impedance for EN = High
and P
Table 6. LOP - LOM Port Differential Input Impedance
vs Frequency for EN = High and P
RF Section
After upconversion, the RF outputs of the I and Q mixers are
combined. An on-chip buffer performs internal differential
to single-ended conversion, while transforming the output
impedance to 50Ω. Table 7 shows the RF port output
impedance vs frequency for EN = High.
LO
= 140MHz, V
FREQUENCY
LO
(MHz)
1000
1250
1500
1800
= 10dBm is given in Table 6.
100
200
400
800
0.1
1.0
2.0
4.0
8.0
16
30
60
CC
= 5V, T = 25°C and single-ended LO
LO
INPUT IMPEDANCE
= 10dBm
LO DIFFERENTIAL
50.9 – j58.9
46.2 – j40.2
37.4 – j28.6
28.3 – j19.4
20.0 – j10.6
20.6 + j10.2
642 – j25.7
64.2 – j104
626 – j112
572 – j204
429 – j305
222 – j287
102 – j181
17.5 – j7.9
16.6 – j2.7
17.3 + j3.3
CC
= 5V it
5598f