ltc5590 Linear Technology Corporation, ltc5590 Datasheet - Page 13

• Manufacturer Part Number: ltc5590
• Description: Dual 600mhz To 1.7ghz High Dynamic Range Downconverting Mixer
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
Introduction
The LTC5590 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.
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 source has DC voltage present, since the primary
side of the RF transformer is internally DC-grounded. The
DC resistance of the primary is approximately 4.5Ω.
Figure 2. Evaluation Board Layout
5590 F02
The secondary winding of the RF transformer is internally
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 is LO frequency-dependent and is not
required for most applications, though it can improve IIP3
in some cases. 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 present at the LO input. The RF input
impedance is also dependent on the LO frequency, as
shown in Figure 4, which shows the RF input return loss
for various LO frequencies with a C1A value of 100pF . A
broadband impedance match is achieved over the 700MHz
to 1.4GHz range. Outside this frequency range, the desired
impedance match can be obtained through adjustment of
external component values.
RFA
C1A
Figure 3. Channel A RF Input Schematic
–10
–15
–20
–25
C8A
–5
0
600
1
2
Figure 4. RF Port Return Loss
RFA
CTA
700
800 900 1000
FREQUENCY (MHz)
LTC5590
1100
TO CHANNEL A
LO = 700MHz
LO = 1090MHz
LO = 1500MHz
MIXER
1200 1300 1400
5590 F03
LTC5590
5590 F04
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