lt5527euf-trpbf Linear Technology Corporation, lt5527euf-trpbf Datasheet - Page 9

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

APPLICATIO S I FOR ATIO
Introduction
The LT5527 consists of a high linearity double-balanced
mixer, RF buffer amplifier, high speed limiting LO buffer
amplifier and bias/enable circuits. The RF and LO inputs
are both single ended. The IF output is differential. Low
side or high side LO injection can be used.
Two evaluation circuits are available. The standard evalu-
ation circuit, shown in Figure 1, incorporates transformer-
based IF matching and is intended for applications that
require the lowest LO-IF leakage levels and the widest IF
bandwidth. The second evaluation circuit, shown in Fig-
ure 2, replaces the IF transformer with a discrete IF balun
for reduced solution cost and size. The discrete IF balun
delivers comparable noise figure and linearity, higher
conversion gain, but degraded LO-IF leakage and reduced
IF bandwidth.
RF Input Port
The mixer’s RF input, shown in Figure 3, consists of an
integrated transformer and a high linearity differential
amplifier. The primary terminals of the transformer are
connected to the RF input pin (Pin 3) and ground. The
secondary side of the transformer is internally connected
to the amplifier’s differential inputs.
One terminal of the transformer’s primary is internally
grounded. If the RF source has DC voltage present, then a
coupling capacitor must be used in series with the RF input
pin.
The RF input is internally matched from 1.7GHz to 3GHz,
requiring no external components over this frequency
range. The input return loss, shown in Figure 4a, is typi-
cally 10dB at the band edges. The input match at the lower
band edge can be optimized with a series 2.7pF capacitor
RF
IN
EXTERNAL MATCHING
FOR LOW BAND OR
HIGH BAND ONLY
L = L (mm)
Z
O
C5
= 50Ω
Figure 3. RF Input Schematic
3
U
RF
U
W
U
5527 F03
TO
MIXER
at Pin 3, which improves the 1.7GHz return loss to greater
than 20dB. Likewise, the 2.7GHz match can be improved
to greater than 30dB with a series 1.5nH inductor. A series
1.5nH/2.7pF network will simultaneously optimize the lower
and upper band edges and expand the RF input bandwidth
to 1.1GHz-3.3GHz. Measured RF input return losses for
these three cases are also plotted in Figure 4a.
Alternatively, the input match can be shifted down, as low
as 400MHz or up to 3700MHz, by adding a shunt capacitor
(C5) to the RF input. A 450MHz input match is realized with
C5 = 12pF, located 4.5mm away from Pin 3 on the evalu-
ation board’s 50Ω input transmission line. A 900MHz in-
put match requires C5 = 3.9pF, located at 1.3mm. A
3500MHz input match is realized with C5 = 0.5pF, located
–10
–15
–25
–30
–20
–10
–15
–25
–30
–20
–5
–5
0
0
0.2
0.2
Figure 4. RF Input Return Loss With
and Without External Matching
L = 4.5mm
SERIES 2.7pF
C5 = 12pF
(4a) Series Reactance Matching
450MHz
0.7
0.7
(4b) Series Shunt Matching
1.2
1.2
RF FREQUENCY (GHz)
SERIES 1.5nH
FREQUENCY (GHz)
NO EXTERNAL
1.7
1.7
900MHz
C5 = 3.9pF
L = 1.3mm
MATCHING
NO EXTERNAL
MATCHING
2.2
2.2
2.7
2.7
SERIES 1.5nH
SERIES 2.7pF
L = 4.5mm
C5 = 0.5pF
3.2
3.2
3.5GHz
3.7
3.7
5527 F04b
5527 F04a
4.2
4.2
LT5527
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5527f