lt5557 Linear Technology Corporation, lt5557 Datasheet - Page 11

• Manufacturer Part Number: lt5557
• Description: 400mhz To 3.8ghz 3.3v High Linearity Downconverting Rf Mixer
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
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,
0dBm LO drive is recommended for optimum noise figure,
although –3dBm will still deliver good conversion gain
and linearity.
Custom matching networks can be designed using the
port impedance data listed in Table 2. This data is refer-
enced to the LO pin with no external matching.
Table 2. LO Input Impedance vs Frequency
IF Output Port
The IF outputs, IF
collectors of the mixer switching transistors (see Fig-
ure 7). Both pins must be biased at the supply voltage,
which can be applied through the center tap of a trans-
former or through matching inductors. Each IF pin draws
26.6mA of supply current (53.2mA total). For optimum
single-ended performance, these differential outputs
should be combined externally through an IF transformer
or a discrete IF balun circuit. The standard evaluation
board (see Figure 1) includes an IF transformer for
impedance transformation and differential to single-ended
transformation. A second evaluation board (see Figure 2)
realizes the same functionality with a discrete IF balun
circuit.
FREQUENCY
(MHz)
1200
1500
1800
2200
2600
3000
3500
4000
4500
5000
300
500
700
900
50
+
and IF
IMPEDANCE
U
11.8 – j10.1
18.8 + j10.9
35.0 + j27.4
72.9 + j19.3
70.0 – j12.6
55.0 – j17.0
82.1 – j13.9
69.0 – j30.1
43.7 – j13.2
36.4 + j19.8
10.0 – j326
8.5 – j41.9
47.8 – j9.7
53.6 – j1.9
66.7 + j0.7
INPUT
–
U
, are internally connected to the
W
0.991
0.820
0.632
0.474
0.350
0.241
0.196
0.167
0.102
0.039
0.143
0.263
0.290
0.154
0.271
MAG
S11
U
ANGLE
–155.9
–107.5
–17.4
–99.2
151.8
100.8
–26.1
–64.3
–97.2
–26.8
–17.4
–43.5
111.6
31.3
2.1
The IF output impedance can be modeled as 560Ω in
parallel with 2.6pF at low frequencies. An equivalent
small-signal model (including bondwire inductance) is
shown in Figure 8. Frequency-dependent differential IF
output impedance is listed in Table 3. This data is refer-
enced to the package pins (with no external components)
and includes the effects of IC and package parasitics. The
IF output can be matched for IF frequencies as low as
several kHz or as high as 600MHz.
Table 3. IF Output Impedance vs Frequency
Two methods of differential to single-ended IF matching
are described:
• Transformer - Based Bandpass
• Discrete IF balun
FREQUENCY (MHz)
Figure 7. IF Output with External Matching
Figure 8. IF Output Small-Signal Model
140
190
240
300
360
450
600
70
1
V
R
CC
S
C
0.7nH
S
0.7nH
IF
IF
+
–
11
10
IF
IF
5557 F07
+
–
DIFFERENTIAL OUTPUT
IMPEDANCE (R
560 || – j63.7k (2.6pF)
509 || – j200 (2.66pF)
448 || – j125 (2.83pF)
11
10
396 || – j92 (2.88pF)
556 || – j870 (2.6pF)
551 || – j440 (2.6pF)
523 || – j320 (2.6pF)
529 || – j254 (2.6pF)
483 || – j163 (2.7pF)
5557 F08
C3
L1
R
IF
V
|| X
LT5557
CC
IF
IF
|| X
8:1
11
IF
)
5557fa
IF
50Ω
OUT