Circuit Note

CN-0211

Rev. 0 | Page 3 of 6

Figure 4 shows test results from the circuit evaluation PCB

when the ADG904R switches are selecting the 856656 SAW

filter. The response compares well to the standalone response,

which is also included in the plot for reference. Due to the loss

of the two ADG904-R switches in series, the insertion loss of

the filter has increased by 1 dB. Ripple in the pass band is of

importance in wireless infrastructure applications. The ripple

across the band is 0.47 dB from the minimum to maximum

peak within the pass band of 135.5 MHz to 144.5 MHz. This

level is well within the data sheet specification for ripple, which

is 0.8 dB max. The high off isolation of the switches is critical in

this application to minimize leakage from one filter channel to

the next. Poor switch off isolation would increase the in-band

insertion loss and ripple of the filter. No evidence of this is

visible in these test results.

Figure 5 and Figure 6 show the 856592 and 856684 SAW filter

channel test results, respectively. The results shown include the

loss from the two ADG904-R switches in series. This loss is

approximately 1.0 dB. Both filter channels show good flat

insertion loss, plus high out-of-band attenuation levels. The

results shown are within the manufacturers data sheet

tolerances and clearly show that the ADG904-R switches are not

introducing any ripple, mismatch, or affecting the flatness of the

filters in any way.

–90

–80

–70

–60

–50

–40

–30

–20

–10

0

105

115

125

135

145

155

165

175

FREQUENCY (MHz)

–7

–8

–9

–10

–11

–12

–13

–14

130

132

134

136

138

140

142

144

146

148

150

FREQUENCY (MHz)

Figure 3. Standalone 140 MHz (Center Frequency), 11.82 MHz (1 dB BW), 856656 SAW Filter Frequency Response, No Switches

–90

–80

–70

–60

–50

–40

–30

–20

–10

0

105

115

125

135

145

155

165

175

FREQUENCY (MHz)

SAW FILTER

SAW FILTER + SW

–7

–8

–9

–10

–11

–12

–13

–14

130

132

134

136

138

140

142

144

146

148

150

FREQUENCY (MHz)

SAW FILTER

SAW FILTER + SW

Figure 4. 140 MHz (Center Frequency), 11.82 MHz (1 dB BW), 856656 SAW Filter Frequency Response Measured on Evaluation Board with and without Switches