LTC5543
14
5543f
APPLICATIONS INFORMATION
Measured IF output return losses for transformer-based
bandpass IF matching (190MHz and 305MHz IF frequency)
and discrete Balun IF matching (456MHz IF frequency) are
plotted in Figure 12.
Figure 11. Conversion Gain and IIp3 vs RF Frequency Using a
456MHz Discrete IF Balun
RF FREQUENCY (GHz)
2.6
19
IIP3 (dBm)
G
C
(dB)
25
27
23
21
29
4
10
12
8
6
14
2.8 4.23 3.2 3.4
5543 F11
3.6 3.8 4
V
CCIF
= 5.0V
V
CCIF
= 3.3V
IF = 456MHz
LOW-SIDE LO
G
C
IIP3
Figure 12. IF Output Return Loss
IF FREQUENCY (MHz)
140
30
IF PORT RETURN LOSS (dB)
15
10
5
20
25
0
180 220 260 300
5543 F12
340 380 420 460 500 540
190MHz IF
305MHz IF
456MHz IF
(DISCRETE BALUN)
IF Amplifi er Bias
The IF amplifi er delivers excellent performance with
V
CCIF
= 3.3V, which allows the V
CC
and V
CCIF
supplies
to be common. With V
CCIF
increased to 5V, the RF input
P1dB increases by more than 3dB, at the expense of higher
power consumption. Mixer performance at 2500MHz is
shown in Table 5 with V
CCIF
= 3.3V and 5V. For the highest
conversion gain, high-Q wire-wound chip inductors are
recommended for L1 and L2, especially when using
V
CCIF
= 3.3V. Low-cost multilayer chip inductors may be
substituted, with a slight degradation in performance.
Table 5. Performance Comparison with V
CCIF
= 3.3V and 5V
(RF = 2500MHz, High-Side LO, IF = 190MHz)
V
CCIF
(V)
I
CCIF
(mA)
G
C
(dB)
P1dB
(dBm)
IIP3
(dBm)
NF
(dB)
3.3 102 8.4 10.9 24.5 10.2
5 105 8.4 13.9 24.5 10.3
The IFBIAS pin (pin 20) is available for reducing the DC
current consumption of the IF amplifi er, at the expense of
reduced performance. This pin should be left open-circuited
for optimum performance. The internal bias circuit produces
a 4mA reference for the IF amplifi er, which causes the
amplifi er to draw approximately 102mA. If resistor R1 is
connected to pin 20 as shown in Figure 7, a portion of the
reference current can be shunted to ground, resulting in
reduced IF amplifi er current. For example, R1 = 1k will
shunt away 1.5mA from pin 20 and the IF amplifi er current
will be reduced by 38% to approximately 62mA. The nominal,
open-circuit DC voltage at pin 20 is 2.1V. Table 6 lists RF
performance at 2500MHz versus IF amplifi er current.
Table 6. Mixer Performance with Reduced IF Amplifi er Current
(RF = 2500MHz, High-Side LO, IF = 190MHz, V
CC
= V
CCIF
= 3.3V)
R1
(kΩ)
I
CCIF
(mA)
G
C
(dB)
IIP3
(dBm)
P1dB
(dBm)
NF
(dB)
OPEN 102 8.4 24.5 10.9 10.2
4.7 90 8.3 24.1 11 10.1
2.2 81 8.1 23.5 11 10.2
1 62 7.7 21.6 11 10.2
(RF = 3500MHz, Low-Side LO, IF = 190MHz, V
CC
= V
CCIF
= 3.3V)
R1
(kΩ)
I
CCIF
(mA)
G
C
(dB)
IIP3
(dBm)
P1dB
(dBm)
NF
(dB)
OPEN 100 6.7 25.1 11.3 11.8
4.7 90 6.4 24.7 11.4 11.7
2.2 82 6.1 24.2 11.5 11.8
1 64 5.3 23.2 11.4 12.1
Shutdown Interface
Figure 13 shows a simplifi ed schematic of the SHDN pin
interface. To disable the chip, the SHDN voltage must be
higher than 3.0V. If the shutdown function is not required,
the SHDN pin should be connected directly to GND. The
voltage at the SHDN 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.
