LTC5591_15 Datasheet, PDF (17/20 Pages) Linear Technology – Dual 1.3GHz to 2.3GHz High Dynamic Range Downconverting Mixer

LTC5591
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.
0
L1, L2 = 180nH
5
L1, L2 = 56nH
10
15
20
25
L1, L2 = 100nH
30
35
50
90 130 170 210 250
IF FREQUENCY (MHz)
5591 F12
Figure 12. IF Output Return Loss with Lowpass Matching
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.
Table 4. Performance Comparison with V_CCIF = 3.3V and 5V
(RF = 1950MHz, Low Side LO, IF = 190MHz, ENA = ENB = High)
V_CCIF
R2A
I_CCIF
G_C
P1dB IIP3
NF
(V)
(Ω) (mA) (dB) (dBm) (dBm) (dB)
Open 200
8.5
10.7 26.2
9.9
3.3
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
IIP3
P1dB
NF
(dB)
(dBm) (dBm)
(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
IIP3
P1dB
NF
(dB)
(dBm) (dBm)
(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
5591f
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