LTC5592
12
5592fa
For more information www.linear.com/LTC5592
Introduction
The LTC5592 consists of two identical mixer channels
driven by a common LO input signal. Each high linearity
mixer consists of a passive double-balanced mixer core,
IF buffer amplifier, LO buffer amplifier and bias/enable
circuits. See the Pin Functions and Block Diagram sections
for a description of each pin. Each of the mixers can be
shutdown independently to reduce power consumption and
low current mode can be selected that allows a trade-off
between performance and power consumption. The RF and
LO inputs are single-ended and are internally matched to
50Ω. Low side or high side LO injection can be used. The
IF outputs are differential. The evaluation circuit, shown in
Figure 1, utilizes bandpass IF output matching and an IF
transformer to realize a 50Ω single-ended IF output. The
evaluation board layout is shown in Figure 2.
applicaTions inForMaTion
Figure 2. Evaluation Board Layout (DC1710A)
The secondary winding of the RF transformer is inter-
nally connected to the channel A passive mixer core. The
center-tap of the transformer secondary is connected to
Pin 2 (CTA) to allow the connection of bypass capacitor,
C8A. The value of C8A can be adjusted to improve channel
isolation at specific RF frequencies with minor impact to
conversion gain, linearity and noise performance. When
used, it should be located within 2mm of Pin 2 for proper
high frequency decoupling. The nominal DC voltage on
the CTA pin is 1.2V.
For the RF inputs to be properly matched, the appropriate
LO signal must be applied to the LO input. A broadband
input match is realized with C1A = 22pF. The measured
input return loss is shown in Figure 4 for LO frequencies
of 1.7GHz, 2.16GHz and 2.5GHz. As shown in Figure 4,
the RF input impedance is dependent on LO frequency,
although a single value of C1A is adequate to cover the
1.7GHz to 2.5GHz RF band.
RF Inputs
The RF inputs of channels A and B are identical. The RF
input of channel A, shown in Figure 3, is connected to the
primary winding of an integrated transformer. A 50Ω match
is realized when a series external capacitor, C1A, is con
-
nected to the RF input. C1A is also needed for DC blocking
if the sour
ce has DC voltage present, since the primar
y
side of the RF transformer is internally DC-grounded. The
DC resistance of the primary is approximately 3.9Ω.
Figure 3. Channel A RF Input Schematic
Figure 4. RF Port Return Loss
5592 F02
LTC5592
C1A
C8A
RFA
CTA
RFA
TO CHANNEL A
MIXER
1
2
5592 F03
FREQUENCY (MHz)
1500
–25
–20
RETURN LOSS (dB)
–15
–10
0
–5
1700
5592 F04
1900 2100
2300
2500
2700
LO = 1700MHz
LO = 2160MHz
LO = 2500MHz
