ADL5565 AD [Analog Devices], ADL5565 Datasheet - Page 21

• Manufacturer Part Number: ADL5565
• Description: 6 GHz Ultrahigh Dynamic Range Differential Amplifier
• Manufacturer: AD [Analog Devices]

By designing a narrow band-pass antialiasing filter between the
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outside of the intended Nyquist zone can be attenuated, helping
to preserve the available SNR of the ADC. In general, the SNR
improves several decibels when including a reasonable order anti-
aliasing filter. In this example, a low loss 1:1 input transformer is
used to match the
source, resulting in minimum insertion loss at the input.
Figure 41 is optimized for driving some of Analog Devices popular
ADCs, such as the AD9467. Table 10 includes antialiasing filter
component recommendations for popular IF sampling frequencies.
Inductor L5 works in parallel with the on-chip ADC input
Table 10. Interface Filter Recommendations for Various IF Sampling Frequencies
Center Frequency (MHz)
96
140
170
211
and the target ADC, the output noise of the
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balanced input to a 50 Ω unbalanced
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1 dB Bandwidth (MHz)
30
40
32
33
Figure 41. Narrow-Band IF Sampling Solution for an ADC Application
1nF
1nF
4Ω
4Ω
L1
L1
C2
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L3
L3
Rev. 0 | Page 21 of 28
C4
105Ω
105Ω
L1 (nH)
3.3
3.3
3.3
3.3
CML
capacitance and a portion of the capacitance presented by C4 to
form a resonant tank circuit. The resonant tank helps to ensure
that the ADC input looks like a real resistance at the target center
frequency. The inductor, L5, shorts the ADC inputs at dc, which
introduces a zero into the transfer function. In addition, the ac
coupling capacitors 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 10 provides initial suggestions for proto-
typing purposes. Some empirical optimization may be needed
to help compensate for actual PCB parasitics.
L5
C2 (pF)
47
47
56
47
AD9467
L3 (nH)
27
27
27
27
C4 (pF)
75
27
18
15
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L5 (nH)
82
150
120
51