CN-0211

Circuit Note

Rev. 0 | Page 4 of 6

–8

–9

–10

–11

–12

–13

–14

125

130

135

140

145

150

155

FREQUENCY (MHz)

–90

–80

–70

–60

–50

–40

–30

–20

–10

0

105

115

125

135

145

155

165

175

FREQUENCY (MHz)

Figure 5. 140 MHz (Center Frequency) 20.7 MHz (1 dB BW) 856592 SAW Filter Frequency Response Measured on Evaluation Board with Switches

–90

–80

–70

–60

–50

–40

–30

–20

–10

0

105

115

125

135

145

155

165

175

FREQUENCY (MHz)

–9.0

–12.0

–11.5

–10.5

–9.5

–10.0

–11.0

–13.0

–12.5

–13.5

–14.0

130

135

140

145

150

FREQUENCY (MHz)

Figure 6. 140 MHz (Center Frequency) 16.18 MHz (1 dB BW) 856684 SAW Filter Frequency Response Measured on Evaluation Board with Switches

COMMON VARIATIONS

The absorptive version of the ADG904 switch can also be used

in this filter bank switching circuit. The absorptive version

contains 50 Ω shunt resistors on the RFx ports. This results in a

good 50 Ω match when the switch is in the off state. This is

important in some applications where reflected signals in the

off channels need to be absorbed.

The circuit can be easily scaled to include more or fewer filter

channels. Depending on the number of channels, other switches

from the ADG9xx family may be better to use and offer more

flexibility with layout. The ADG936 is a dual SPDT switch, the

ADG918 is an SPDT switch, and the ADG901 is an SPST

switch. All of these switches are available in both absorptive and

reflective configurations.

CIRCUIT EVALUATION AND TEST

The circuit is designed to be connected to a vector network

analyzer (VNA) via SMA type connectors. The SMA connectors

on the board are female. To switch between each filter channel

there are jumper terminals on the board that can be manually

changed. Note that one of the switch throws in each ADG904-R

switch is not used. Therefore, when these unused switches are

selected, the RF input and RF output ports are isolated, i.e., the

switches are not connected to a filter.