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LTC5591IUH#PBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P20
LTC5591
13
5591f
Introduction
The LTC5591 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
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 3.6Ω.
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 the
channel-to-channel isolation at specific RF operation
frequency with minor impact to conversion gain, linearity
and noise performance. The channel-to-channel isola-
tion performance with different values of C8A is given in
Figure 4. 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.
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
Figure 3. Channel A RF Input Schematic
Figure 4. Channel-to-Channel Isolation vs C8 Values
RF FREQUENCY (MHz)
1250
30
CHANNEL ISOLATION (dB)
40
45
50
1650
2050
2250
5591 F04
35
1450 1850
2450
55
C8 OPEN
C8 = 2.2pF
C8 = 2.7pF
C8 = 3.3pF
5591 F02
LTC5591
C1A
C8A
RFA
CTA
RFA
TO CHANNEL A
MIXER
1
2
5591 F03
LTC5591
14
5591f
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 = 2.2pF. The measured
input return loss is shown in Figure 4 for LO frequencies
of 1.4GHz, 1.75GHz and 2GHz. These LO frequencies
correspond to lower, middle and upper values in the LO
range. As shown in Figure 5, the RF input impedance is
dependent on LO frequency, although a single value of C1A
is adequate to cover the 1.3GHz to 2.3GHz RF band.
applicaTions inForMaTion
Figure 6. LO Input Schematic
LO Input
The LO input, shown in Figure 6, is connected to the
primary winding of an integrated transformer. A 50Ω
impedance match is realized at the LO port by adding
an external series capacitor, C2. This capacitor is also
needed for DC blocking if the LO source has DC voltage
present, since the primary side of the LO transformer is
DC-grounded internally. The DC resistance of the primary
is approximately 4.1Ω.
The secondary of the transformer drives a pair of high
speed limiting differential amplifiers for channels A and B.
The LTC5591’s LO amplifiers are optimized for the 1.4GHz
to 2.1GHz LO frequency range; however, LO frequencies
outside this frequency range may be used with degraded
performance.
The LO port is always 50Ω matched when V
CC
is applied,
even when one or both of the channels is disabled. This
helps to reduce frequency pulling of the LO source when
LO
TO
MIXER B
LTC5591
I
SEL
5591 F06
18
LO
16
17
ENA
ENB
C2
14
BIAS
BIAS
TO
MIXER A
Figure 5. RF Port Return Loss
The RF input impedance and input reflection coefficient,
versus RF frequency, are listed in Table 1. The reference
plane for this data is pin 1 of the IC, with no external
matching, and the LO is driven at 1.75GHz.
Table 1. RF Input Impedance and S11
(at Pin 1, No External Matching, f
LO
= 1.75GHz)
FREQUENCY
(GHz)
RF INPUT
IMPEDANCE
S11
MAG ANGLE
1.0 25.3 + j34.6 0.51 100.8
1.2 33.7 + j38.7 0.46 88.1
1.4 43.8 + j38.6 0.39 76.8
1.6 56.0 + j33.5 0.31 62.3
1.8 48.1 + j9.1 0.09 96.4
2.0 38.5 + j21.4 0.27 104.6
2.2 40.1 + j28.3 0.32 91.8
2.4 44.0 + j34.7 0.35 79.6
2.6 52.1 + j40.7 0.37 65.3
2.8 64.1 + j44.1 0.38 51.2
3.0 78.8 + j42.0 0.38 37.5
RF FREQUENCY (GHz)
1
60
RF PORT RETURN LOSS (dB)
30
40
20
10
1.4
2
2.2 2.4 2.6 2.81.8
5591 F05
50
1.2 1.6
3
0
LO = 1.4GHz
LO = 1.75GHz
LO = 2GHz
LTC5591
15
5591f
Figure 7. LO Input Return Loss
the mixer is switched between different operating states.
Figure 7 illustrates the LO port return loss for the different
operating modes.
applicaTions inForMaTion
return pin (IFGNDA), and a pin for adjusting the internal
bias (IFBA). The IF outputs must be biased at the sup-
ply voltage (V
CCIFA
), which is applied through matching
inductors L1A and L2A. Alternatively, the IF outputs can
be biased through the center tap of a transformer (T1A).
The common node of L1A and L2A can be connected to
the center tap of the transformer. Each IF output pin draws
approximately 50mA of DC supply current (100mA total).
An external load resistor, R2A, can be used to improve
impedance matching if desired.
IFGNDA (Pin 23) must be grounded or the amplifier will
not draw DC current. Inductor L3A may improve LO-IF
and RF-IF leakage performance in some applications, but
is otherwise not necessary. Inductors should have small
resistance for DC. High DC resistance in L3A will reduce
the IF amplifier supply current, which will degrade RF
performance.
Figure 8. IF Amplifier Schematic with Bandpass Match
4:1
T1A
IFA
C7A
L2AL1A
C5A
R2A
L3A (OR SHORT)
V
CCIFA
20212223
IF
AMP
BIAS
100mA
4mA
IFBA
V
CCA
LTC5591
IGNDA
IFA
–
IFA
+
R1A
(OPTION TO
REDUCE
DC POWER)
The nominal LO input level is 0dBm, though the limiting
amplifiers will deliver excellent performance over a ±6dBm
input power range. Table 2 lists the LO input impedance
and input reflection coefficient versus frequency.
Table 2. LO Input Impedance vs Frequency
(at Pin 16, No External Matching, ENA = ENB = High)
FREQUENCY
(GHz)
INPUT
IMPEDANCE
S11
MAG ANGLE
1.0 39.4 + j46.4 0.47 75.5
1.2 55.3 + j40.8 0.36 61.4
1.4 61.9 + j26.8 0.25 52.6
1.6 56.5 + j16.1 0.16 59.5
1.8 47.6 + j14.0 0.14 91.6
2.0 41.6 + j18.0 0.21 103.9
2.2 38.4 + j23.5 0.29 101.5
2.4 37.1 + j30.7 0.36 93.3
2.6 38.4 + j38.3 0.42 83.3
2.8 42.0 + j47.6 0.47 72.2
3.0 48.6 + j56.1 0.49 61.8
IF Outputs
The IF amplifiers in channels A and B are identical. The IF
amplifier for channel A, shown in Figure 8, has differen-
tial open collector outputs (IFA
+
and IFA
–
), a DC ground
LO FREQUENCY (GHz)
1
LO1 PORT RETURN LOSS (dB)
1.4
2
2.2 2.4 2.6 2.81.8
5591 F07
1.2 1.6
0.8
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
BOTH CHANNELS ON
ONE
CHANNEL ON
BOTH CHANNELS OFF
For optimum single-ended performance, the differential
IF output must be combined through an external IF
transformer or a discrete IF balun circuit. The evaluation
board (see Figures 1 and 2) uses a 4:1 IF transformer for
impedance transformation and differential to single-ended
conversion. It is also possible to eliminate the IF transformer
and drive differential filters or amplifiers directly.
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P20

LTC5591IUH#PBF

Mfr. #:
Buy LTC5591IUH#PBF
Manufacturer:
Analog Devices Inc.
Description:
RF Mixer Dual 1.3GHz 2.3GHz High Dynamic Range Mixer
Lifecycle:
New from this manufacturer.
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