lt5527euf-trpbf Linear Technology Corporation, lt5527euf-trpbf Datasheet - Page 10

• Manufacturer Part Number: lt5527euf-trpbf
• Description: 400mhz To 3.7ghz High Signal Level Downconverting Mixer
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
LT5527
at 4.5mm. This series transmission line/shunt capacitor
matching topology allows the LT5527 to be used for mul-
tiple frequency standards without circuit board layout
modifications. The series transmission line can also be
replaced with a series chip inductor for a more compact
layout.
Input return loss for these three cases (450MHz, 900MHz
and 3500MHz) are plotted in Figure 4b. The input return
loss with no external matching is repeated in Figure 4b for
comparison.
RF input impedance and S11 versus frequency (with no
external matching) is listed in Table 1 and referenced to
Pin 3. The S11 data can be used with a microwave circuit
simulator to design custom matching networks and simu-
late board-level interfacing to the RF input filter.
Table 1. RF Input Impedance vs Frequency
LO Input Port
The mixer’s LO input, shown in Figure 5, consists of an
integrated transformer and high speed limiting differential
amplifiers. The amplifiers are designed to precisely drive
the mixer for the highest linearity and the lowest noise
figure. An internal DC blocking capacitor in series with the
transformer’s primary eliminates the need for an external
blocking capacitor.
10
FREQUENCY
(MHz)
1200
1500
1850
2150
2450
2650
3000
3500
4000
5000
300
450
600
900
50
IMPEDANCE
U
11.9 + j15.3
14.3 + j18.2
19.4 + j23.8
26.1 + j29.8
37.3 + j33.9
57.4 + j29.7
71.3 + j10.1
64.6 – j13.9
53.0 – j21.8
35.0 – j21.2
10.4 + j31.9
9.0 + j11.9
20.7 – j9.0
14.2 + j6.2
4.8 + j2.6
INPUT
U
W
0.825
0.708
0.644
0.600
0.529
0.467
0.386
0.275
0.193
0.175
0.209
0.297
0.431
0.564
0.745
MAG
S11
U
ANGLE
–111.2
–155.8
173.9
152.5
144.3
137.2
123.2
107.4
–36.8
–70.3
164.8
113.3
89.3
60.6
20.6
The LO input is internally matched from 1.2GHz to 5GHz,
although the maximum useful frequency is limited to
3.5GHz by the internal amplifiers. The input match can be
shifted down, as low as 750MHz, with a single shunt
capacitor (C4) on Pin 15. One example is plotted in
Figure 6 where C4 = 2.7pF produces an 850MHz to
1.2GHz match.
LO input matching below 750MHz requires the series
inductor (L4)/shunt capacitor (C4) network shown in
Figure 5. Two examples are plotted in Figure 6 where L4 =
3.9nH/C4 = 5.6pF produces a 650MHz to 830MHz match
and L4 = 6.8nH/C4 = 10pF produces a 540MHz to 640MHz
match. The evaluation boards do not include pads for L4,
so the circuit trace needs to be cut near Pin 15 to insert L4.
A low cost multilayer chip inductor is adequate for L4.
The optimum LO drive is –3dBm for LO frequencies above
1.2GHz, although the amplifiers are designed to accom-
modate several dB of LO input power variation without
significant mixer performance variation. Below 1.2GHz,
LO
IN
FOR LOW BAND
MATCHING
EXTERNAL
ONLY
C4
L4
–10
–20
–30
–15
–25
–5
0
0.1
Figure 6. LO Input Return Loss
Figure 5. LO Input Schematic
15
LO
L4 = 6.8nH
C4 = 10pF
V
L4 = 3.9nH
C4 = 5.6pF
LO FREQUENCY (GHz)
CC2
V
BIAS
1
L4 = 0nH
C4 = 2.7pF
MATCHING
EXTERNAL
NO
5527 F06
5
LIMITER
5527 F05
TO
MIXER
5527f