AD9222
Rev. C | Page 42 of 60
ALTERNATIVE ANALOG INPUT DRIVE
CONFIGURATION
In this example, a 16 MHz, two-pole low-pass filter was applied
to the AD8334 outputs. The following components need to be
removed and/or changed:
The following is a brief description of the alternative analog
input drive configuration using the AD8334 dual VGA. If this
drive option is in use, some components may need to be
populated, in which case all the necessary components are listed
in Table 17. For more details on the AD8334 dual VGA,
including how it works and its optional pin settings, consult the
AD8334 data sheet.
• Remove L507, L508, L511, L512, L515, L516, L519, L520,
L607, L608, L611, L612, L615, L616, L619, and L620 on the
AD8334 analog outputs.
• Populate L507, L508, L511, L512, L515, L516, L519, L520,
L607, L608, L611, L612, L615, L616, L619, and L620 with
680 nH inductors.
To configure the analog input to drive the VGA instead of the
default transformer option, the following components need to
be removed and/or changed.
• Populate C543, C547, C551, C555, C643, C647, C651, and
C655 with a 68 pF capacitor.
68pF
680nH
680nH
05967-107
• Remove R102, R115, R128, R141, R161, R162, R163, R164,
R202, R208, R218, R225, R234, R241, R252, R259, T101,
T102, T103, T104, T201, T202, T203, and T204 in the
default analog input path.
Figure 88. Example Filter Configured for16 MHz, Two-Pole Low-Pass Filter
0
–120
–100
–80
–60
–40
–20
05.07.52.5 10.0 15.0 17.512.5 20.0 22.5 25.0
AMPLITUDE (dBFS)
FREQUENCY (MHz)
05967-108
fSAMPLE
=50MSPS
AIN = 3.5MHz
AD8334 = MAX GAIN SETTING
• Populate R101, R114, R127, R140, R201, R217, R233, and
R251 with 0 Ω resistors in the analog input path.
• Populate R152, R153, R154, R155, R156, R157, R158, R159,
R215, R216, R229, R230, R247, R248, R263, R264, C103,
C105, C110, C112, C117, C119, C124, C126, C203, C205,
C210, C212, C217, C219, C224, and C226 with 10 kΩ
resistors to provide an input common-mode level to the
ADC analog inputs.
• Populate R105, R113, R118, R124, R131, R137, R151, R160,
R205, R213, R221, R222, R237, R238, R255, and R256 with
0 Ω resistors in the ADC analog input path to connect the
VGA outputs.
Figure 89. AD9222 FFT Example Results Using 16 MHz, Two-Pole Low-Pass
Filter Applied to the AD8334 Outputs (fSAMPLE = 50 MSPS, AIN = 3.5 MHz,
AD8334 = Maximum Gain Setting, Analog Input Signal = −1.03 dBFS, SNR =
60.8 dBc, SFDR = 67.02 dBc)
• Remove R515, R520, R527, R532, R615, R620, R627, and
R632 on the AD8334 analog outputs.
• Remove R512, R524, R612, and R624 to set the AD8334
mode and AD8334 HILO pin low. Some applications may
require this to be different. Consult the AD8334 data sheet
for more information on these functions.
In this configuration, L505 to L520 and L605 to L620 are
populated with 0 Ω resistors to allow signal connection and use
of a filter if additional requirements are necessary.