LT5557EUF-PBF LINER [Linear Technology], LT5557EUF-PBF Datasheet - Page 14

• Manufacturer Part Number: LT5557EUF-PBF
• Description: 400MHz to 3.8GHz 3.3V High Signal Level Downconverting Mixer
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
LT5557
Differential IF Output Matching
For fully differential IF architectures, the mixer’s IF out-
puts can be matched directly into a SAW filter or IF
amplifier, thus eliminating the IF transformer. One ex-
ample is shown in Figure 13, where the mixer’s 500Ω
differential output resistance is matched into a 100Ω
differential SAW filter using the tapped-capacitor tech-
nique. Inductors L1 and L2 form the inductive portion of
the matching network, cancel the internal 2.6pF capaci-
tance, and supply DC bias current to the mixer core.
Capacitors C6 through C9 are the capacitive portion of the
matching, and perform the impedance step-down.
The calculations for tapped-capacitor matching are cov-
ered in the literature, and are not repeated here. Other
differential matching options include low-pass, high-
pass and band-pass. The choice depends on the system
14
DECOUPLING
Standard Evaluation Board Layout (DC1131A)
Figure 13. Differential IF Matching Using
the Tapped-Capacitor Technique
SUPPLY
IF
IF
+
–
U
C1
L1
L2
U
C2
V
CC
C6
C7
C8
C9
W
FILTER
SAW
AMP
IF
5557 F13
U
performance goals, IF frequency, IF bandwidth and filter
(or amplifier) input impedance. Contact the factory for
applications assistance.
Enable Interface
Figure 14 shows a simplified schematic of the EN pin
interface. The voltage necessary to turn on the LT5557 is
2.7V. To disable the chip, the enable voltage must be less
than 0.3V. If the EN pin is allowed to float, the chip will tend
to remain in its last operating state. Thus it is not recom-
mended that the enable function be used in this manner.
If the shutdown function is not required, then the EN pin
should be connected directly to V
The voltage at the EN pin should never exceed the power
supply voltage (V
occur, the supply current could be sourced through the
EN pin ESD diode, potentially damaging the IC.
Discrete IF Evaluation Board Layout (DC910A)
Figure 14. Enable Input Circuit
CC
5
EN
) by more than 0.3V. If this should
V
CC2
LT5557
CC
22k
5557 F14
.
5557fa