Datasheet

AD9244
Rev. C | Page 26 of 36
EVALUATION BOARD
ANALOG INPUT CONFIGURATION
Table 12 provides a summary of the analog input configuration.
The analog inputs of the AD9244 on the evaluation board can
be driven differentially through a transformer via Connector S4,
or through the
AD8138 amplifier via Connector S2, or they can
be driven single-ended directly via Connector S3. When using
the transformer or
AD8138 amplifier, a single-ended source can
be used, as both of these devices are configured on the AD9244
evaluation board to convert single-ended signals to differential
signels.
Optimal AD9244 performance is achieved above 500 kHz by
using the input transformer. To drive the AD9244 via the trans-
former, connect solderable Jumper JP45 and Jumper JP46. DC
bias is provided by Resistor R8 and Resistor R28. The evaluation
board has positions for through-hole and surface-mount
transformers.
For applications requiring lower frequencies or dc applications,
the
AD8138 can be used. The AD8138 provides good distortion
and noise performance, as well as input buffering up to 30 MHz.
For more information, refer to the
AD8138 data sheet. To use
the
AD8138 to drive the AD9244, remove the transformer (T1
or T4) and connect solderable Jumper JP42 and Jumper JP43.
The AD9244 can be driven single-ended directly via S3 and can
be ac-coupled or dc-coupled by removing or inserting JP5. To
run the evaluation board in this way, remove the transformer
(T1 or T4) and connect solderable Jumper JP40 and Jumper JP41.
Resistor R40, Resistor R41, Resistor R8, and Resistor R28 are
used to bias the AD9244 inputs to the correct common-mode
levels in this application.
REFERENCE CONFIGURATION
As described in the Analog Input and Reference Overview
section, the AD9244 can be configured to use its own internal
or an external reference. An external reference, D3, and refer-
ence buffer, U5, are included on the AD9244 evaluation board.
Jumper JP8 and Jumper JP22 to Jumper JP24 can be used to
select the desired reference configuration (see
Table 13).
CLOCK CONFIGURATION
The AD9244 evaluation board was designed to achieve optimal
performance as well as to be easily configurable by the user. To
configure the clock input, begin by connecting the correct com-
bination of solderable jumpers (see
Table 14). The specific
jumper configuration is dependent on the application and can
be determined by referring to the
Clock Input Modes section. If
the differential clock input mode is selected, an external sine
wave generator applied to S5 can be used as the clock source.
The clock buffer/drive MC10EL16 from ON Semiconductor® is
used on the evaluation board to buffer and square the clock
input. If the single-ended clock configuration is used, an exter-
nal clock source can be applied to S1.
The AD9244 evaluation board generates a buffered clock at
TTL/CMOS levels for use with a data capture system, such as
the HSC-ADC-EVAL-SC system. The clock buffering is pro-
vided by U4 and U7 and is configured by Jumper JP3,
Jumper JP4, Jumper JP9, and Jumper JP18 (see
Table 14).
Table 12. Analog Input Jumper Configuration
Analog Input Input Connector Jumpers Notes
Differential: Transformer S4 45, 46 R8, R28 provide dc bias; optimal for 500 kHz.
Differential: Amplifier S2 42, 43 Remove T1 or T4; used for low input frequencies.
Single-Ended S3 5, 40, 41 Remove T1 or T4. JP5: connected for dc-coupled, not connected for ac-coupling.
Table 13. Reference Jumper Configuration
Reference Voltage Jumpers Notes
Internal 2 V 23 JP8 not connected
Internal 1 V 24 JP8 not connected
Internal 1 V ≤ VREF ≤ 2 V 25 JP8 not connected; VREF = 1 + R1/R2
External 1 V ≤ VREF ≤ 2 V 8, 22 Set VREF with R26