AD8376ACPZ-WP(RevA) View Datasheet(PDF) - Analog Devices
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AD8376ACPZ-WP Datasheet PDF : 24 Pages
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Figure 42 is optimized for driving some of Analog Devices
popular unbuffered ADCs, such as the AD9246, AD9640,
and AD6655. Table 5 includes antialiasing filter component
recommendations for popular IF sampling center frequencies.
Inductor L5 works in parallel with the on-chip ADC input
capacitance and a portion of the capacitance presented by C4 to
form a resonant tank circuit. The resonant tank helps to ensure
the ADC input looks like a real resistance at the target center
frequency. Additionally, the L5 inductor shorts the ADC inputs
AD8376
at dc, which introduces a zero into the transfer function. In
addition, the ac coupling capacitors and the bias chokes introduce
additional zeros into the transfer function. The final overall
frequency response takes on a band-pass characteristic, helping
to reject noise outside of the intended Nyquist zone. Table 5
provides initial suggestions for prototyping purposes. Some
empirical optimization may be needed to help compensate for
actual PCB parasitics.
1nF
1:3
1µH
1nF L1
L3
50Ω
1/2
165Ω
1nF AD8376
301Ω C2
C4 CML
L5
165Ω
L1
L3
1nF
5
1µH
AD9246
AD9640
AD6655
A0 TO A4
Figure 42. Narrow-Band IF Sampling Solution for Unbuffered ADC Applications
Table 5. Interface Filter Recommendations for Various IF Sampling Frequencies
Center Frequency
1 dB Bandwidth
L1
C2
96 MHz
27 MHz
390 nH
5.6 pF
140 MHz
30 MHz
330 nH
3.3 pF
170 MHz
32 MHz
270 nH
2.7 pF
211 MHz
32 MHz
220 nH
2.2 pF
L3
390 nH
330 nH
270 nH
220 nH
C4
25 pF
20 pF
20 pF
18 pF
L5
100 nH
56 nH
39 nH
27 nH
Rev. A | Page 17 of 24
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