LT5525EUF View Datasheet(PDF) - Linear Technology
Part Name
Description
Manufacturer
LT5525EUF Datasheet PDF : 12 Pages
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LT5525
APPLICATIO S I FOR ATIO
RF+
2
LT5525
OPTIONAL SERIES
REACTANCE FOR
LOW BAND OR
RFIN
HIGH BAND
MATCHING
RF–
3
5525 F02
Figure 2. RF Input Schematic
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.
0
–5
NO RF
MATCHING
–10
–15
–20
–25
–30
500
SERIES 1.2nH
SERIES 3.9pF
1000 1500 2000 2500 3000
RF FREQUENCY (MHz)
5525 F03
Figure 3. RF Input Return Loss Without and
with External Matching Components
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– pin with the RF+ pin grounded (no
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
25
20
IIP3
15
SSB NF
10
5
TA = 25°C
fIF = 140MHz
LOW SIDE LO
HIGH SIDE LO
0
GAIN
–5
800 850 900 950 1000 1050 1100 1150 1200
RF FREQUENCY (MHz)
5525 F04
Figure 4. Typical Gain, IIP3 and NF with
Series 3.9pF Matching Capacitor
Table 1. RF Port Input Impedance vs Frequency
FREQUENCY
(MHz)
INPUT
IMPEDANCE
REFLECTION COEFFICIENT
MAG
ANGLE
50
10.4 + j2.63
0.675
174
500
18.1 + j23.7
0.551
124
700
25.8 + j30.7
0.478
106
900
36.5 + j34.5
0.398
90
1100
48.4 + j33.3
0.321
74
1300
59.5 + j25.7
0.244
57
1500
65.9 + j13.1
0.177
33
1700
65.0 – j1.0
0.131
–3
1900
59.0 – j12.2
0.138
–47
2100
50.2 – j19.0
0.187
–79
2300
41.8 – j22.1
0.250
–97
2500
34.9 – j22.7
0.311
–109
2700
29.1 – j21.9
0.369
–118
3000
23.2 – j19.1
0.435
–130
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+ and LO– pins are designed for
5525f
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