AD9772A
90
AD9772A EVALUATION BOARD
75MHz
The AD9772-EB is an evaluation board for the AD9772A TxDAC.
Careful attention to layout and circuit design, combined with
prototyping area, allows the user to easily and effectively evalu-
ate the AD9772A in different modes of operation.
85
125MHz
275MHz
80
75
Referring to Figures 37 and 38, the AD9772A’s performance
can be evaluated differentially or single-endedly using a trans-
former, differential amplifier, or directly coupled output. To
evaluate the output differentially using the transformer, remove
jumpers JP12 and JP13 and monitor the output at J6 (IOUT).
To evaluate the output differentially, remove the transformer
(T2) and install jumpers JP12 and JP13. The output of the
amplifier can be evaluated at J13 (AMPOUT). To evaluate the
AD9772A single-endedly and directly coupled, remove the
transformer and jumpers (JP12 and JP13) and install resistors
R16 or R17 with 0 Ω.
325MHz
70
65
60
55
50
–14
–12
–10
–8
–6
– dBFS
–4
–2
0
A
OUT
Figure 35. Dual-Tone “Windowed” SFDR vs. AOUT
fDATA = 100 MSPS
@
The digital data to the AD9772A comes across a ribbon cable
which interfaces to a 40-pin IDC connector. Proper termination
or voltage scaling can be accomplished by installing RN2 and/or
RN3 SIP resistor networks. The 22 Ω DIP resistor network,
RN1, must be installed and helps reduce the digital data edge
rates. A single-ended CLOCK input can be supplied via the
ribbon cable by installing JP8 or more preferably via the SMA
connector, J3 (CLOCK). If the CLOCK is supplied by J3, the
AD9772A can be configured for a differential clock interface by
installing jumpers JP1 and configuring JP2, JP3, and JP9 for the
DF position. To configure the AD9772A clock input for a single-
ended clock interface, remove JP1 and configure JP2, JP3 and
JP9 for the SE position.
For many applications, the data update rate to the DAC (i.e.,
fDATA) must be some fixed integer multiple of some system
reference clock (i.e., GSM – 13 MHz). Furthermore, these
applications prefer to use standard IF frequencies which offer
a large selection of SAW filter choices of varying passbands
(i.e., 70 MHz). These applications may still benefit from the
AD9772A’s direct IF mode capabilities when used in conjunc-
tion with a digital upconverter such as the AD6622. Since the
AD6622 can digitally synthesize and tune up to four modulated
carriers, it is possible to judiciously tune these carriers in a region
which may fall within an IF filter’s passband upon reconstruc-
tion by the AD9772A. Figure 36 shows an example in which
four carriers were tuned around 18 MHz with a digital upcon-
verter operating at 52 MSPS such that when reconstructed by
the AD9772A in the IF MODE, these carriers fall around a
70 MHz IF.
The AD9772A’s PLL clock multiplier can be disabled by con-
figuring jumper JP5 for the L position. In this case, the user
must supply a clock input at twice (2ϫ) the data rate via J3
(CLOCK). The 1ϫ clock is made available on SMA con-
nector J1 (PLLLOCK), and should be used to trigger a pattern
generator directly or via a programmable pulse generator. Note
that PLLLOCK is capable of providing a 0 V to 0.85 V output
into a 50 Ω load. To enable the PLL clock multiplier, JP5 must
be configured for the H position. In this case, the clock may be
supplied via the ribbon cable (i.e., JP8 installed) or J3 (CLOCK).
The divide-by-N ratio can be set by configuring JP6 (DIV0) and
JP7 (DIV1).
–10
–20
–30
–40
–50
–60
–70
The AD9772A can be configured for Baseband or Direct IF Mode
operation by configuring jumpers JP11 (MOD0) and JP10
(MOD1). For baseband operation, JP10 and JP11 should be
configured in the L position. For direct IF operation, JP10 and
JP11 should be configured in the H position. For direct IF
operation without “zero-stuffing,” JP11 should be configured in
the H position while JP10 should be configured in the low position.
–80
–90
–110
66
68
70
72
74
FREQUENCY – MHz
The AD9772A’s voltage reference can be enabled or disabled
via JP4 (EXT REF IN). To enable the reference, configure JP in
the INT position. A voltage of approximately 1.2 V will appear
at the TP6 (REFIO) test point. To disable the internal refer-
ence, configure JP4 in the EXT position and drive TP6 with an
external voltage reference. Lastly, the AD9772A can be placed
in the SLEEP mode by driving the TP11 test point with logic
level HIGH input signal.
Figure 36. Spectral Plot of Four Carriers at 60 MHz IF
with fDATA = 52 MSPS, PLLVDD = 0
–24–
REV. A
ADI [ ADI ]
