CN-0268 Datasheet, PDF (4/6 Pages) Analog Devices – Resonant Approach to Designing a Band-Pass Filter for Narrow-Band, High IF, 16-Bit, 250 MSPS Receiver Front End

CN-0268
Figure 6 and Figure 7 shows the resulting antialiasing filter
response with a 1 dB bandwidth of 41 MHz and a 3 dB bandwidth
of 89 MHz, centered at an IF of 203 MHz. Figure 8 shows the FFT
spectrum for the final receiver circuit of Figure 1, where the SNR is
72.5 dBFS, and the SFDR performance approaches 90 dBc.
20.000
14.286
8.571
2.857
–2.857
–8.571
–14.286
–20.000
0
100
200
300
400
FREQUENCY (MHz)
Figure 6. Antialiasing Filter Response, fC = 203 MHz
0
–0.5
–1.0
1dB BW = 41MHz
–1.5
–2.0
–2.5
–3.0
3dB BW = 89MHz
–3.5
120
140
160
180
200
220
240
FREQUENCY (MHz)
Figure 7. Antialiasing Filter Response, fC = 203 MHz, 1 dB and 3 dB Bandwidth
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–110
–120
–130
0
f_IN = 203MHz
f_S = 245.76MHz
SNR = 72.5dB
SFDR = –88.9dBc
H2/H3 = –89.1dBc/–88.9dBc
20
40
60
80
100
120
FREQUENCY (MHz)
Figure 8. Single Tone FFT Plot, Input = 203 MHz,
Sampling Rate = 245.76 MSPS
Circuit Note
Using ADS as a simulation tool, the filter components can
be further tuned to shift the resonant peak to the desired IF.
For example, by changing the parallel 8.2 pF capacitor of the
antialiasing filter to 10 pF shifts the resonance peak lower to
180 MHz. Figure 9 through Figure 11 show the filter profile
and single-tone FFT performance for this condition.
20.000
14.286
8.571
2.857
–2.857
–8.571
–14.286
–20.000
0
100
200
300
400
FREQUENCY (MHz)
Figure 9. Antialiasing Filter Response, fC = 183 MHz
0
–0.5
–1.0
1dB BW = 40MHz
–1.5
–2.0
–2.5
–3.0
3dB BW = 75MHz
–3.5
100 120 140 160 180 200 220 240
FREQUENCY (MHz)
Figure 10. Antialiasing Filter Response, fC = 183 MHz,
1 dB and 3 dB Bandwidth
0
–10
f_IN = 183MHz
f_S = 245.76MHz
–20
SNR = 73dB
–30
SFDR = –91dBc
H2/H3 = –94dBc/–91dBc
–40
–50
–60
–70
–80
–90
–100
–110
–120
–130
0
20
40
60
80
100
120
FREQUENCY (MHz)
Figure 11. Single Tone FFT Plot, Input = 183 MHz,
Sampling Rate = 245.76 MSPS
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