LTC5576
14
5576fa
For more information www.linear.com/LTC5576
Introduction
The LTC5576 uses a high performance LO buffer amplifier
driving a double-balanced mixer core to achieve frequency
conversion with high linearity. A differential common-
emitter stage at the mixer input allows very broad band
matching of the input. The Block Diagram and Pin Func
-
tions sections provide additional details. The LTC5576
is primarily intended for upmixer applications, however,
due to its broadband input capability, it could be used as
a downmixer as well.
The test circuit schematic in Figure 1 shows the external
component values used for the IC characterization. The
evaluation board layout is shown in Figure 2. Additional
components may be used to optimize performance for
different applications.
The single-ended LO port is impedance matched over a
very broad frequency range for ease of use. Low side or
high side LO injection can be used, though the value of R1
may need to be adjusted accordingly for best performance.
The IC includes an internal RF balun at the mixer output,
thus the OUT port is single-ended. External components
are required to optimize the impedance match for the
desired frequency range.
applicaTions inForMaTion
IN Port
A simplified schematic of the mixer’s input path is shown
in Figure 3. The IN
+
and IN
–
pins drive the bases of the
input transistors while internal R-C networks are used for
impedance matching. The input pins are internally biased to
a common-mode voltage of 1.6V, thus external DC block
-
ing capacitors, C1 and C2 are required. A small value of
C3 can be used to extend the impedance match to higher
fr
equencies. The 1:1 transformer provides single-ended to
differential signal conversion for optimum performance.
Single-ended operation is possible by driving one input
pin and connecting the unused input pin to RF ground
through a capacitor. The performance will be degraded
but may be acceptable at lower frequencies.
Figure 2. LTC5576 Evaluation Board Layout
Figure 3. IN Port with External Matching
IN
V
CC
T1
1:1
5576 F03
C3
C2
V
BIAS
LGND
V
BIAS
LTC5576
C1
IN
+
IN
–
3
4
2
V
CC
V
CC
5576 F02
