lt5525 Linear Technology Corporation, lt5525 Datasheet - Page 8

• Manufacturer Part Number: lt5525
• Description: High Linearity, Low Power Downconverting Mixer
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
LT5525
Figure 4 illustrates the typical conversion gain, IIP3 and NF
performance of the LT5525 when the RF input match is
shifted lower in frequency using an external series 3.9pF
capacitor on the RF input.
RF input impedance and reflection coefficient (S11) ver-
sus frequency are shown in Table 1. The listed data is
referenced to the RF
external matching). This information can be used to simu-
late board-level interfacing to an input filter, or to design
a broadband input matching network.
8
As shown in Figure 3, the RF input return loss with no
external matching is greater than 12dB from 1.3GHz to
2.3GHz. The RF input match can be shifted down to
800MHz by adding a series 3.9pF capacitor at the RF input.
A series 1.2nH inductor can be added to shift the match up
to 2.5GHz. Measured return losses with these external
components are also shown in Figure 3.
RF
IN
Figure 3. RF Input Return Loss Without and
with External Matching Components
OPTIONAL SERIES
–10
–15
–20
–25
–30
REACTANCE FOR
LOW BAND OR
–5
0
HIGH BAND
MATCHING
500
Figure 2. RF Input Schematic
1000
U
SERIES 3.9pF
–
RF FREQUENCY (MHz)
MATCHING
pin with the RF
2
3
1500
RF
RF
NO RF
U
+
–
2000
SERIES 1.2nH
W
2500
+
pin grounded (no
5525 F03
3000
LT5525
U
5525 F02
Table 1. RF Port Input Impedance vs Frequency
A broadband RF input match can be easily realized by
using both the series capacitor and series inductor as
shown in Figure 5. This network provides good return loss
at both lower and higher frequencies simultaneously,
while maintaining good mid-band return loss. The broad-
band return loss is plotted in Figure 6. The return loss is
better than 12dB from 700MHz to 2.6GHz using the
element values of Figure 5.
LO Input Port
The LO buffer amplifier consists of high speed limiting
differential amplifiers designed to drive the mixer core for
high linearity. The LO
FREQUENCY
(MHz)
1100
1300
1500
1700
1900
2100
2300
2500
2700
3000
500
700
900
50
Figure 4. Typical Gain, IIP3 and NF with
Series 3.9pF Matching Capacitor
10
25
20
15
–5
0
5
800
IIP3
SSB NF
GAIN
850
IMPEDANCE
10.4 + j2.63
18.1 + j23.7
25.8 + j30.7
36.5 + j34.5
48.4 + j33.3
59.5 + j25.7
65.9 + j13.1
59.0 – j12.2
50.2 – j19.0
41.8 – j22.1
34.9 – j22.7
29.1 – j21.9
23.2 – j19.1
65.0 – j1.0
900
INPUT
RF FREQUENCY (MHz)
+
950
and LO
1000
1050
T
f
IF
A
–
= 140MHz
= 25°C
REFLECTION COEFFICIENT
LOW SIDE LO
HIGH SIDE LO
1100
pins are designed for
0.675
0.551
0.478
0.398
0.321
0.244
0.177
0.131
0.138
0.187
0.250
0.311
0.369
0.435
MAG
1150
5525 F04
1200
ANGLE
–109
–118
–130
174
124
106
–47
–79
–97
90
74
57
33
–3
5525f