Data Sheet
AD9763/AD9765/AD9767
Rev. G | Page 29 of 44
500
225
25
AD8055
IOUTA
IOUTB
225
COPT
AVDD
1k
AD9763/
AD9765/
AD9767
0
06
17-
0
74
Figure 74. Single-Supply DC Differential-Coupled Circuit
SINGLE-ENDED, UNBUFFERED VOLTAGE OUTPUT
Figure 75 shows the AD9763/AD9765/AD9767 configured to
provide a unipolar output range of approximately 0 V to 0.5 V
for a doubly terminated 50 Ω cable, because the nominal full-
scale current (IOUTFS) of 20 mA flows through the equivalent
RLOAD of 25 Ω. In this case, RLOAD represents the equivalent load
resistance seen by IOUTA or IOUTB. The unused output (IOUTA or IOUTB)
can be connected directly to ACOM or via a matching RLOAD.
Different values of IOUTFS and RLOAD can be selected as long as the
positive compliance range is adhered to. One additional
section). For optimum INL performance, the single-ended,
buffered voltage output configuration is suggested.
50
25
50
VOUTA = 0V TO 0.5V
IOUTFS = 20mA
IOUTA
IOUTB
AD9763/
AD9765/
AD9767
00
61
7-
0
75
Figure 75. 0 V to 0.5 V Unbuffered Voltage Output
SINGLE-ENDED, BUFFERED VOLTAGE OUTPUT
CONFIGURATION
Figure 76 shows a buffered single-ended output configuration
in which the U1 op amp performs an I-V conversion on the
AD9763/AD9765/AD9767 output current. U1 maintains IOUTA
(or IOUTB) at a virtual ground, thus minimizing the nonlinear
output impedance effect on the INL performance of the DAC,
ended configuration typically provides the best dc linearity
performance, its ac distortion performance at higher DAC update
rates may be limited by the slewing capabilities of U1. U1
provides a negative unipolar output voltage, and its full-scale
output voltage is simply the product of RFB and IOUTFS. Set the
full-scale output within U1’s voltage output swing capabilities
by scaling IOUTFS and/or RFB. An improvement in ac distortion
performance may result with a reduced IOUTFS because the signal
current U1 has to sink will be subsequently reduced.
IOUTFS = 10mA
U1
IOUTA
IOUTB
VOUT = IOUTFS × RFB
COPT
200
RFB
200
AD9763/
AD9765/
AD9767
00
61
7-
0
76
Figure 76. Unipolar Buffered Voltage Output
POWER AND GROUNDING CONSIDERATIONS
Power Supply Rejection
Many applications seek high speed and high performance under
less than ideal operating conditions. In these applications, the
implementation and construction of the printed circuit board is
as important as the circuit design. Proper RF techniques must
be used for device selection, placement, and routing as well as
power supply bypassing and grounding to ensure optimum
printed circuit board ground, power, and signal plane layouts
that are implemented on the AD9763/AD9765/AD9767
evaluation board.
One factor that can measurably affect system performance is
the ability of the DAC output to reject dc variations or ac noise
superimposed on the analog or digital dc power distribution.
This is referred to as the power supply rejection ratio (PSRR).
For dc variations of the power supply, the resulting performance
of the DAC directly corresponds to a gain error associated with
the DAC’s full-scale current, IOUTFS. AC noise on the dc supplies
is common in applications where the power distribution is
generated by a switching power supply. Typically, switching
power supply noise occurs over the spectrum of tens of
kilohertz to several megahertz. The PSRR vs. frequency of the
AD9763/AD9765/AD9767 AVDD supply over this frequency
90
70
85
80
75
P
S
RR
(
d
B)
0.20.3
0.40.50.60.70.80.91.01.1
FREQUENCY (MHz)
00
61
7-
0
77
Figure 77. AVDD Power Supply Rejection Ratio vs. Frequency