lt5522 Linear Technology Corporation, lt5522 Datasheet - Page 11

• Manufacturer Part Number: lt5522
• Description: 600mhz To 2.7ghz High Signal Level Downconverting Mixer
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
Table 1. RF Port Input Impedance vs Frequency
RF input impedance and S11 versus frequency are shown
in Table 1. The listed data is referenced to the RF
the RF
mation can be used to simulate board-level interfacing to
an input filter, or to design a broadband input matching
network.
A broadband RF input match is easily realized using the
shunt inductor/series capacitor network shown in Fig-
ure 6. This network provides good return loss at low and
high frequencies simultaneously, with reasonable
midband return loss. As shown in Figure 7, the RF input
return loss is greater than 12dB from 715MHz to 2.3GHz
using the element values shown in Figure 6. The input
match is optimum at 850MHz and 1900MHz, ideal for tri-
band GSM applications.
FREQUENCY
(MHZ)
1100
1300
1500
1700
1900
2100
2300
2500
2700
3000
500
700
900
50
+
pin grounded (no external matching). This infor-
Figure 6. Wideband RF Input Matching
RFIN
10nH
L3
U
IMPEDANCE
19.5 + j20.6
24.1 + j24.2
28.6 + j26.1
33.7 + j26.2
39.5 + j24.3
45.6 + j18.9
45.6 – j13.2
38.0 – j19.9
30.4 – j22.8
24.5 – j23.0
18.7 – j20.9
10.4 + j2.6
50.2 + j9.7
50.5 – j2.2
3.3pF
INPUT
C5
U
2
3
RF
RF
+
–
W
0.660
0.507
0.454
0.407
0.353
0.285
0.199
0.096
0.023
0.143
0.259
0.360
0.440
0.525
MAG
LT5522
5522 F06
S11
U
–
ANGLE
–100.7
–108.3
–114.8
–120.7
–129.4
173.5
129.5
118.7
111.1
104.4
–76.0
pin with
98.2
92.0
83.0
LO Input Port
The LO buffer amplifier consists of high speed limiting
differential amplifiers, designed to drive the mixer quad for
high linearity. The LO
single-ended drive, although differential drive can be used
if a differential LO source is available. A schematic is
shown in Figure 8. Measured return loss is shown in
Figure 9.
The LO source must be AC-coupled to avoid forward
biasing the ESD diodes. If the LO source has DC voltage
present, then a coupling capacitor must be used in series
with the LO input pin.
LO input impedance and S11 versus frequency are shown
in Table 2. The listed data is referenced to the LO
the LO
LO IN
–
pin grounded.
–10
–15
–20
–25
–5
0
1E8
Figure 7. RF Input Return Loss
Using Wideband Matching Network
14
15
Figure 8. LO Input Schematic
LO
LO
+
–
480Ω
RF FREQUENCY (Hz)
+
and LO
1E9
15pF
15pF
–
pins are designed for
5522 F07
5E9
LT5522
+
LT5522
TO
MIXER
pin with
11
5522 F08
5522fa