LT5527 データシートの表示（PDF） - Linear Technology
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LT5527 Datasheet PDF : 20 Pages
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LTC5590
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.
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 applied to the LO input. A broadband
input match is realized with C1A = 100pF. The measured
input return loss is shown in Figure 4 for LO frequencies
of 0.7GHz, 1.09GHz and 1.5GHz. These LO frequencies
correspond to lower, middle and upper values in the LO
range. 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 700MHz to 1.5GHz RF band.
RFA C1A
RFA
1
CTA
2
C8A
LTC5590
TO CHANNEL A
MIXER
5590 F02
Figure 2. Evaluation Board Layout
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.
5590 F03
Figure 3. Channel A RF Input Schematic
0
LO = 700MHz
LO = 1090MHz
–5
LO = 1500MHz
–10
–15
–20
C1 = 100pF
–25
600 700 800 900 1000 1100 1200 1300 1400
FREQUENCY (MHz)
5590 F04
Figure 4. RF Port Return Loss
5590p
13
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