LT5522
10
5522fa
RF FREQUENCY(GHz)
0.2
PORT RETURN LOSS (dB)
0
–5
–10
–15
–20
–25
–30
1.7 2.7
5522 F05
0.7 1.2
2.2 3.2 3.7
NO EXTERNAL
MATCH
C5 = 2.2pF
(900MHz)
L3 = 3.9nH
(HIGH BAND)
C5 = 8.2pF
L = 5mm
(450MHz)
APPLICATIO S I FOR ATIO
WUUU
Introduction
The LT5522 consists of a high linearity double-balanced
mixer, RF buffer amplifier, high speed limiting LO buffer
amplifier and bias/enable circuits. The IC has been opti-
mized for downconverter applications where the RF input
signal is in the 400MHz to 2.7GHz range and the LO signal
is in the 400MHz to 2.7GHz range. Operation over a wider
RF input frequency range is possible with reduced
performance.
The IF output can be matched for IF frequencies as low as
100kHz or as high as 1GHz. The RF, LO and IF ports are all
differential, although the RF and LO ports are internally
matched for single-ended drive as shown in Figure 2. The
LT5522 is characterized and production-tested with single-
ended RF and LO drive. Low side or high side LO injection
can be used.
Two evaluation boards are available. The standard board
is intended for most applications, including cellular, PCS,
UMTS and 2.4GHz. A schematic is shown in Figure 2 and
the board layout is shown in Figure 18. The 140MHz IF
output frequency on the standard board is easily changed
by modifying the IF matching elements. The second board,
intended for CATV applications, incorporates a wideband
IF output balun. The CATV evaluation schematic is shown
in Figure 3 and the board layout is shown in Figure 19.
RF Input Port
The mixer’s RF input, shown in Figure 4, consists of an
integrated balun and a high linearity differential amplifier.
The primary terminals of the balun are connected to the
RF
+
and RF
–
pins (Pins 2 and 3, respectively). The second-
ary side of the balun is internally connected to the amplifier’s
differential inputs. For single-ended operation, the RF
+
pin
is grounded and the RF
–
pin becomes the RF input. It is
also possible to ground the RF
–
pin and drive the RF
+
pin,
although the LO to RF isolation will degrade slightly.
The RF source must be AC-coupled since one terminal of
the balun’s primary is grounded. If the RF source has DC
voltage present, then a coupling capacitor must be used in
series with the RF input pin.
As shown in Figure 5, the RF input return loss, with no
external matching, is greater than 10dB from 1.2GHz to
2.4GHz. The RF input match can be shifted down in
frequency by adding a shunt capacitor at the RF input. Two
examples are plotted in Figure 5. A 2.2pF capacitor,
located near Pin 3, produces a 900MHz match. An 8.2pF
capacitor, located 5mm away from Pin 3 (on the 50Ω line),
produces a 450MHz match. The RF input match can also
be shifted up in frequency by adding a shunt inductor near
Pin 3. One example is plotted in Figure 5, where a 3.9nH
inductor produces a 2.3GHz to 2.8GHz match.
2
RF
+
LT5522
3
RF
–
RF IN
C5
OPTIONAL SHUNT
REACTANCE
FOR LOW BAND
OR HIGH BAND
MATCHING (C5 OR L3)
TO
MIXER
5522 F04
Figure 4. RF Input Schematic
Figure 5. RF Input Return Loss
