ADL5350

Rev. 0 | Page 20 of 24

Figure 63 depicts a crossover filter network approach to provide

isolation between the RF and IF ports for a downconverting

application. The crossover network essentially provides a high-

pass filter to allow the RF signal to pass to the RF/IF node (Pin 1

and Pin 8), while presenting a low-pass filter (which is actually

a band-pass filter when considering the dc blocking capacitor,

passed to the desired IF load.

RF/IF

GND2

LOIN

NC

RF/IF

NC

VPOS

3.8nH

100pF

C2

1.8pF

L2

1.5nH

100pF

C1

1.2pF

LO

100pF

2.2nH

RF

3V

IF

GND1

ADL5350

12

3

4

87

6

5

L1

3.5nH

4.7µF

ALL

INDUCTORS

ARE 0302CS

SERIES FROM

COILCRAFT

Figure 63. 3.3 GHz to 3.8 GHz RF Downconversion Schematic

When designing the RF port and IF port networks, it is

important to remember that the networks share a common

node (the RF/IF pins). In addition, the opposing network presents

some loading impedance to the target network being designed.

Classic audio crossover filter design techniques can be applied

to help derive component values. However, some caution must be

applied when selecting component values. At high RF frequencies,

the board parasitics can significantly influence the final optimum

inductor and capacitor component selections. Some empirical

testing may be necessary to optimize the RF and IF port filter

networks. The performance of the circuit depicted in Figure 63

is provided in Figure 64.

30

25

20

15

10

5

0

14

2

4

6

8

10

12

3300

3800

3700

3600

3500

3400

RF FREQUENCY (MHz)

IIP3

IP1dB

LOSS

Figure 64. Measured Performance for Circuit in Figure 63

Using Low-Side LO Injection and 800 MHz IF