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LTC5591IUH#PBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P20
LTC5591
16
5591f
At IF frequencies, the IF output impedance can be modeled
as 300Ω in parallel with 2.3pF. The equivalent small-signal
model, including bondwire inductance, is shown in Figure 9.
Frequency-dependent differential IF output impedance is
listed in Table 3. This data is referenced to the package
pins (with no external components) and includes the ef-
fects of IC and package parasitics.
applicaTions inForMaTion
Figure 10. IF Output Return Loss with Bandpass Matching
Values of L1A and L2A are tabulated in Figure 1 for vari-
ous IF frequencies. The measured IF output return loss
for bandpass IF matching is plotted in Figure 10.
Figure 11. IF Output with Lowpass Matching
Figure 9. IF Output Small-Signal Model
22
21
IFA
+
IFA
–
0.9nH0.9nH
R
IF
C
IF
LTC5591
5591 F09
Bandpass IF Matching
The bandpass IF matching configuration, shown in Figures
1 and 8, is best suited for IF frequencies in the 90MHz to
500MHz range. Resistor R2A may be used to reduce the IF
output resistance for greater bandwidth and inductors L1A
and L2A resonate with the internal IF output capacitance
at the desired IF frequency. The value of L1A, L2A can be
estimated as follows:
L1A = L2A =
1
2πf
IF
( )
2
• 2 • C
IF
where C
IF
is the internal IF capacitance (listed in Table 3).
Table 3. IF Output Impedance vs Frequency
FREQUENCY (MHz)
DIFFERENTIAL OUTPUT
IMPEDANCE (R
IF
||
X
IF
(C
IF
))
90 321 || –j769 (2.3pF)
140 307 || –j494 (2.3pF)
190 300 || –j364 (2.3pF)
240 292 || –j286 (2.3pF)
300 285 || –j225 (2.4pF)
380 276 || –j177 (2.4pF)
500 264 || –j122 (2.6pF)
Lowpass IF Matching
For IF frequencies below 90MHz, the inductance values
become unreasonably high and the lowpass topology
shown in Figure 11 is preferred. This topology also can
provide improved RF to IF and LO to IF isolation. V
CCIFA
is supplied through the center tap of the 4:1 transformer.
A lowpass impedance transformation is realized by shunt
elements R2A and C9A (in parallel with the internal RIF and
CIF), and series inductors L1A and L2A. Resistor R2A is
used to reduce the IF output resistance for greater band-
width, or it can be deleted for the highest conversion gain.
The final impedance transformation to 50Ω is realized by
transformer T1A. The measured IF output return loss for
IF FREQUENCY (MHz)
100
IF PORT RETURN LOSS (dB)
150
250
300 350 400 450
5591 F10
200
50
0
5
10
15
20
30
25
L1, L2 = 270nH
L1, L2 = 150nH
L1, L2 = 100nH
L1, L2 = 56nH
4:1
T1A
IFA
50Ω
V
CCIFA
3.1 TO 5.3V
C5A
2122
IFA
–
IFA
+
C6
C9A
R2A
L1A L2A
LTC5591
5591 F11
LTC5591
17
5591f
Figure 12. IF Output Return Loss with Lowpass Matching
applicaTions inForMaTion
lowpass IF matching with R2A and C9A open is plotted
in Figure 12. The LTC5591 demo board (see Figure 2) has
been laid out to accommodate this matching topology with
only minor modifications.
Table 4. Performance Comparison with V
CCIF
= 3.3V and 5V
(RF = 1950MHz, Low Side LO, IF = 190MHz, ENA = ENB = High)
V
CCIF
(V)
R2A
(Ω)
I
CCIF
(mA)
G
C
(dB)
P1dB
(dBm)
IIP3
(dBm)
NF
(dB)
3.3
Open 200 8.5 10.7 26.2 9.9
1k 200 7.4 11.5 26.5 9.9
5 Open 207 8.4 13.9 26.7 10.1
The IFBA pin (Pin 20) is available for reducing the DC
current consumption of the IF amplifier, at the expense of
IIP3. The nominal DC voltage at Pin 20 is 2.1V, and this pin
should be left open-circuited for optimum performance.
The internal bias circuit produces a 4mA reference for the
IF amplifier, which causes the amplifier to draw approxi-
mately 100mA. If resistor R1A is connected to Pin 20 as
shown in Figure 8, a portion of the reference current can
be shunted to ground, resulting in reduced IF amplifier
current. For example, R1A = 470Ω will shunt away 1.4mA
from Pin 20 and the IF amplifier current will be reduced
by 35% to approximately 65mA. Table 5 summarizes RF
performance versus total IF amplifier current when both
channels are enabled.
Table 5. Mixer Performance with Reduced IF Amplifier Current
RF = 1950MHz, Low Side LO, IF = 190MHz, V
CC
= V
CCIF
= 3.3V
R1A, R1B
I
CCIF
(mA)
G
C
(dB)
IIP3
(dBm)
P1dB
(dBm)
NF
(dB)
Open 200 8.5 26.2 10.7 9.9
3.3kΩ 176 8.4 25.7 10.8 9.9
1.0kΩ 151 8.1 24.7 10.9 9.9
470Ω 130 7.9 23.7 10.9 9.9
RF = 1600MHz, High Side LO, IF = 190MHz, V
CC
= V
CCIF
= 3.3V
R1A, R1B
I
CCIF
(mA)
G
C
(dB)
IIP3
(dBm)
P1dB
(dBm)
NF
(dB)
Open 200 8.6 24.6 10.2 10.2
3.3kΩ 176 8.4 24.3 10.4 10.3
1.0kΩ 151 8.1 23.5 10.6 10.3
470Ω 130 7.9 22.7 10.5 10.3
IF Amplifier Bias
The IF amplifier delivers excellent performance with V
CCIF
= 3.3V, which allows a single supply to be used for V
CC
and V
CCIF
. At V
CCIF
= 3.3V, the RF input P1dB of the mixer
is limited by the output voltage swing. For higher P1dB,
in this case, resistor R2A (Figure 7) can be used to reduce
the output impedance and thus the voltage swing, thus
improving P1dB. The trade-off for improved P1dB will be
lower conversion gain.
With V
CCIF
increased to 5V the P1dB increases by over
3dB, at the expense of higher power consumption. Mixer
P1dB performance at 1950MHz is tabulated in Table 4 for
V
CCIF
values of 3.3V and 5V. For the highest conversion
gain, high-Q wire-wound chip inductors are recommended
for L1A and L2A, especially when using V
CCIF
= 3.3V. Low
cost multilayer chip inductors may be substituted, with a
slight reduction in conversion gain.
IF FREQUENCY (MHz)
IF PORT RETURN LOSS (dB)
90 170 210 250
5591 F12
130
50
0
5
10
15
20
25
30
35
L1, L2 = 100nH
L1, L2 = 180nH
L1, L2 = 56nH
LTC5591
18
5591f
Figure 14. ENA Interface Schematic
Low Current Mode
Both mixer channels can be set to low current mode using
the I
SEL
pin. This allows flexibility to choose a reduced
current mode of operation when lower RF performance
is acceptable. Figure 13 shows a simplified schematic of
the I
SEL
pin interface. When I
SEL
is set low (<0.3V), both
channels operate at nominal DC current. When I
SEL
is set
high (>2.5V), the DC currents in both channels are reduced,
thus reducing power consumption. The performance in
low power mode and normal power mode are compared
in Table 6.
applicaTions inForMaTion
LTC5591
17
ENA
500Ω
V
CCA
5591 F14
19
CLAMP
Figure 13. I
SEL
Interface Schematic
LTC5591
18
I
SEL
V
CCB
500Ω
V
CCA
5591 F13
19
BIAS A
BIAS B
Table 6. Performance Comparison Between Different Power Modes
RF = 1950MHz, Low Side LO, IF = 190MHz, ENA = ENB = High
I
SEL
I
TOTAL
(mA)
G
C
(dB)
IIP3
(dBm)
P1dB
(dBm)
NF
(dB)
Low 382 8.5 26.2 10.7 9.9
High 239 7.2 21.4 10.7 10.3
Enable Interface
Figure 14 shows a simplified schematic of the ENA pin
interface (ENB is identical). To enable channel A, the ENA
voltage must be greater than 2.5V. If the enable function
is not required, the enable pin can be connected directly
to V
CC
. The voltage at the enable pin should never exceed
the power supply voltage (V
CC
) by more than 0.3V. If this
should occur, the supply current could be sourced through
the ESD diode, potentially damaging the IC.
The Enable pins must be pulled high or low. If left float-
ing, the on/off state of the IC will be indeterminate. If a
three-state condition can exist at the enable pins, then a
pull-up or pull-down resistor must be used.
Supply Voltage Ramping
Fast ramping of the supply voltage can cause a current
glitch in the internal ESD protection circuits. Depending on
the supply inductance, this could result in a supply volt-
age transient that exceeds the maximum rating. A supply
voltage ramp time of greater than 1ms is recommended.
Spurious Output Levels
Mixer spurious output levels versus harmonics of the
RF and LO are tabulated in Table 7. The spur levels were
measured on a standard evalution board using the test
circuit shown in Figure 1. The spur frequencies can be
calculated using the following equation:
f
SPUR
= (M • f
RF
)–(N • f
LO
)
Table 7. IF Output Spur Levels (dBc)
RF = 1950MHz, P
RF
= –3dBm, P
LO
= 0dBm, P
IF
190MHz, Low Side LO,
V
CC
= 3.3V, V
CCIF
= 3.3V, ENA = ENB = High, I
SEL
= Low, T
C
= 25°C
N
M
0 1 2 3 4 5 6 7 8 9
0 –41 –54 –64 –84 –66 –74 –75 –81 –84
1 –49 0 –56 –42 –68 –77 –75 –70 * –92
2 –82 –83 –70 –77 * * * * * *
3 * –88 * –71
* * * * * *
4 * * * * * * * * * *
5 * * * * * * * * * *
6 * * * * * * * * *
7 * * * * * * –84 *
*Less than –100dBc
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
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