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參數(shù)資料
| 型號： | AD9760-EB |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | 10-Bit, 125 MSPS TxDAC D/A Converter |
| 中文描述： | 10位，125 MSPS的TxDAC系列D / A轉(zhuǎn)換 |
| 文件頁數(shù)： | 16/23頁 |
| 文件大?。?/td> | 412K |
| 代理商： | AD9760-EB |
AD9760
–
16
–
REV. B
APPLYING THE AD9760
OUTPUT CONFIGURATIONS
The following sections illustrate some typical output configura-
tions for the AD9760. Unless otherwise noted, it is assumed
that I
OUTFS
is set to a nominal 20 mA. For applications requir-
ing the optimum dynamic performance, a differential output
configuration is suggested. A differential output configuration
may consist of either an RF transformer or a differential op amp
configuration. The transformer configuration provides the opti-
mum high frequency performance and is recommended for any
application allowing for ac coupling. The differential op amp
configuration is suitable for applications requiring dc coupling, a
bipolar output, signal gain and/or level shifting.
A single-ended output is suitable for applications requiring a
unipolar voltage output. A positive unipolar output voltage will
result if I
OUTA
and/or I
OUTB
is connected to an appropriately
sized load resistor, R
LOAD
, referred to ACOM. This configura-
tion may be more suitable for a single-supply system requiring
a dc coupled, ground referred output voltage. Alternatively, an
amplifier could be configured as an I-V converter, thus convert-
ing I
OUTA
or I
OUTB
into a negative unipolar voltage. This con-
figuration provides the best dc linearity since I
OUTA
or I
OUTB
is
maintained at a virtual ground. Note that I
OUTA
provides slightly
better performance than I
OUTB
.
DIFFERENTIAL COUPLING USING A TRANSFORMER
An RF transformer can be used to perform a differential-to-
single-ended signal conversion as shown in Figure 50. A
differentially coupled transformer output provides the optimum
distortion performance for output signals whose spectral content
lies within the transformer’s passband. An RF transformer such
as the Mini-Circuits T1-1T provides excellent rejection of com-
mon-mode distortion (i.e., even-order harmonics) and noise
over a wide frequency range. It also provides electrical isolation
and the ability to deliver twice the power to the load. Trans-
formers with different impedance ratios may also be used for
impedance matching purposes. Note that the transformer
provides ac coupling only.
R
LOAD
AD9760
22
21
MINI-CIRCUITS
T1-1T
OPTIONAL R
DIFF
I
OUTA
I
OUTB
Figure 50. Differential Output Using a Transformer
The center tap on the primary side of the transformer must be
connected to ACOM to provide the necessary dc current path
for both I
OUTA
and I
OUTB
. The complementary voltages appear-
ing at I
OUTA
and I
OUTB
(i.e., V
OUTA
and V
OUTB
) swing symmetri-
cally around ACOM and should be maintained with the specified
output compliance range of the AD9760. A differential resistor,
R
DIFF
, may be inserted in applications where the output of the
transformer is connected to the load, R
LOAD
, via a passive re-
construction filter or cable. R
DIFF
is determined by the
transformer’s impedance ratio and provides the proper source
termination that results in a low VSWR. Note that approxi-
mately half the signal power will be dissipated across R
DIFF
.
DIFFERENTIAL USING AN OP AMP
An op amp can also be used to perform a differential to single-
ended conversion as shown in Figure 51. The AD9760 is con-
figured with two equal load resistors, R
LOAD
, of 25
. The
differential voltage developed across I
OUTA
and I
OUTB
is con-
verted to a single-ended signal via the differential op amp con-
figuration. An optional capacitor can be installed across I
OUTA
and I
OUTB
, forming a real pole in a low-pass filter. The addition
of this capacitor also enhances the op amps distortion perfor-
mance by preventing the DACs high slewing output from over-
loading the op amp’s input.
AD9760
22
I
OUTA
I
OUTB
21
C
OPT
500
225
225
500
25
25
AD8047
Figure 51. DC Differential Coupling Using an Op Amp
The common-mode rejection of this configuration is typically
determined by the resistor matching. In this circuit, the differ-
ential op amp circuit using the AD8047 is configured to provide
some additional signal gain. The op amp must operate off of a
dual supply since its output is approximately
±
1.0 V. A high
speed amplifier capable of preserving the differential perfor-
mance of the AD9760 while meeting other system level objec-
tives (i.e., cost, power) should be selected. The op amps
differential gain, its gain setting resistor values, and full-scale
output swing capabilities should all be considered when opti-
mizing this circuit.
The differential circuit shown in Figure 52 provides the neces-
sary level-shifting required in a single supply system. In this
case, AVDD which is the positive analog supply for both the
AD9760 and the op amp is also used to level-shift the differ-
ential output of the AD9760 to midsupply (i.e., AVDD/2). The
AD8041 is a suitable op amp for this application.
AD9760
22
I
OUTA
I
OUTB
21
C
OPT
500
225
225
1k
25
25
AD8041
1k
AVDD
Figure 52. Single-Supply DC Differential Coupled Circuit
SINGLE-ENDED UNBUFFERED VOLTAGE OUTPUT
Figure 53 shows the AD9760 configured to provide a unipolar
output range of approximately 0 V to +0.5 V for a doubly termi-
nated 50
cable since the nominal full-scale current, I
OUTFS
, of
20 mA flows through the equivalent R
LOAD
of 25
. In this case,
R
LOAD
represents the equivalent load resistance seen by I
OUTA
or
I
OUTB
. The unused output (I
OUTA
or I
OUTB
) can be connected
to ACOM directly or via a matching R
LOAD
. Different values of
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| AD9760-EBZ | 功能描述:BOARD EVAL FOR AD9760 RoHS:是 類別:編程器，開發(fā)系統(tǒng) >> 評估板 - 數(shù)模轉(zhuǎn)換器 (DAC) 系列:TxDAC® 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:1 系列:- DAC 的數(shù)量:4 位數(shù):12 采樣率（每秒）:- 數(shù)據(jù)接口:串行，SPI? 設(shè)置時間:3µs DAC 型:電流/電壓 工作溫度:-40°C ~ 85°C 已供物品:板 已用 IC / 零件:MAX5581 |
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