Differential Filter Design - Analog Devices AD9912 Quick Start Manual

AD9912/PCBZ

DIFFERENTIAL FILTER DESIGN

The differential filter advantages include fewer components and
a simpler design when the AD9912
Note that the 100 Ω differential source impedance is internal to
the IOUT/IOUB driver. Also, note that the ac coupling between
the IOUT differential pair and the FDBK_IN differential pair is
critical. Component matching between the corresponding LC
sections is important in this design. The example shown in
Figure 6 is for a cutoff of 240 MHz.
INTERNAL TO AD9912
DACOUT/DACOUTB
DRIVER
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
10M
is used in an actual design.
L4
22.0nH
Q = 20.0
C4
11.0pF
Q = 50.0
320MHz
R1 C3 C6
100Ω 10.0pF 14.0pF
Q = 50.0 Q = 50.0
L5
22.0nH
Q = 20.0
C5
11.0pF
Q = 50.0
320MHz
Figure 6. Differential Low-Pass Reconstruction Filter
PHASE
Figure 7. Frequency Response of Differential Reconstruction Filter Shown in Figure 6
th
7 Order Elliptical Differential Low-Pass Filter
•
Pass-band frequency: 240 MHz
•
Pass-band ripple: 1.0 dB
•
Stop-band ratio: 1.3
•
Stop-band frequency: 312 MHz
•
Stop-band attenuation: 70 dB
L7 L10
29.0nH 34.0nH
Q = 20.0 Q = 20.0
C7 C10
6.30pF 2.00pF
Q = 50.0 Q = 50.0
370MHz 610MHz
C9
17.0pF
Q = 50.0
L8 L11
29.0nH 34.0nH
Q = 20.0 Q = 20.0
C8 C11
6.30pF 2.00pF
Q = 50.0 Q = 50.0
370MHz 610MHz
MAGNITUDE
100M
FREQUENCY (Hz)
Rev. 0 | Page 10 of 12
TO FDBK_IN
C12 R13
13.0pF 100Ω
Q = 50.0
TO FDBK_INB
1G
480
400
320
240
160
80
0
–80
–160
–240