參數(shù)資料
型號(hào)： AD9777EB
廠商： Analog Devices, Inc.
英文描述： 16-Bit, 160 MSPS 2X/4X/8X Interpolating Dual TxDAC+ D/A Converter
中文描述： 16位，160 MSPS的2X/4X/8X TxDAC系列插雙D / A轉(zhuǎn)換
文件頁(yè)數(shù)： 37/48頁(yè)
文件大?。?/td> 6021K
代理商： AD9777EB
REV. 0
AD9777
–37–
DIFFERENTIAL COUPLING USING A TRANSFORMER
An RF transformer can be used to perform a differential-to-
single-ended signal conversion as shown in Figure 52. A
differentially coupled transformer output provides the optimum
distortion performance for output signals whose spectral content
lies within the transformer’s pass band. An RF transformer,
such as the Mini-Circuits T1-1T, provides excellent rejection
of common-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.
Transformers with different impedance ratios may also be used
for impedance matching purposes.
I
OUTA
I
OUTB
DAC
R
LOAD
MINI-CIRCUITS
T1-T2
Figure 52. Transformer-Coupled Output Circuit
The center tap on the primary side of the transformer must be
connected to AGND to provide the necessary dc current path
for both I
OUTA
and I
OUTB
. The complementary voltages appearing
at I
OUTA
and I
OUTB
(i.e., V
OUTA
and V
OUTB
) swing symmetrically
around AGND and should be maintained within the specified
output compliance range of the AD9777. 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 recon-
struction 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 approximately half the
signal power will be dissipated across R
DIFF
.
DIFFERENTIAL COUPLING USING AN OP AMP
An op amp can also be used to perform a differential-to-single-
ended conversion as shown in Figure 53. This has the added
benefit of providing signal gain as well. In Figure 53, the AD9777
is configured with two equal load resistors, R
LOAD
, of 25
. The
differential voltage developed across I
OUTA
and I
OUTB
is converted
to a single-ended signal via the differential op amp configuration.
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 amp’s distortion performance by
preventing the DAC’s fast slewing output from overloading the
input of the op amp.
I
OUTA
I
OUTB
DAC
25
AD8021
500
C
OPT
225
225
500
R
OPT
225
AVDD
25
Figure 53. Op Amp-Coupled Output Circuit
The common-mode (and second order distortion) rejection of this
configuration is typically determined by the resistor matching. The
op amp used must operate from a dual supply since its output
is approximately
±
1.0 V. A high speed amplifier, such as the
AD8021, capable of preserving the differential performance of the
APPLYING THE AD9777 OUTPUT CONFIGURATIONS
The following sections illustrate typical output configurations for
the AD9777. Unless otherwise noted, it is assumed that I
OUTFS
is set to a nominal 20 mA. For applications requiring optimum
dynamic performance, a differential output configuration is
suggested. A simple differential output may be achieved by
converting I
OUTA
and I
OUTB
to a voltage output by terminating
them to AGND via equal value resistors. This type of configura-
tion may be useful when driving a differential voltage input device
such as a modulator. If a conversion to a single-ended signal is
desired and the application allows for ac-coupling, an RF trans-
former may be useful; if power gain is required, an op amp may
be used. The transformer configuration provides optimum high
frequency noise and distortion performance. The differential op
amp configuration is suitable for applications requiring dc-
coupling, signal gain, and/or level shifting within the bandwidth of
the chosen op amp.
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 a load resistor,
R
LOAD
, referred to AGND. This configuration is most 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 converting I
OUTA
or I
OUTB
into a negative unipolar voltage. This configuration provides
the best DAC dc linearity as I
OUTA
or I
OUTB
are maintained at
ground or virtual ground.
UNBUFFERED DIFFERENTIAL OUTPUT, EQUIVALENT
CIRCUIT
In many applications, it may be necessary to understand the
equivalent DAC output circuit. This is especially useful when
designing output filters or when driving inputs with finite input
impedances. Figure 51 illustrates the output of the AD9777 and
the equivalent circuit. A typical application where this informa-
tWn may be useful is when designing an interface filter between the
AD9777 and Analog Devices’ AD8345 quadrature modulator.
I
OUTA
R
A
+ R
B
I
OUTB
V
(DIFFERENTIAL)
V
SOURCE
=
(R
A
B
)
I
OUTFS
p-p
V
OUT
+
V
OUT
–
Figure 51. DAC Output Equivalent Circuit
For the typical situation, where I
OUTFS
= 20 mA and R
A
and R
B
both equal 50
, the equivalent circuit values become:
V
SOURCE
= 2 V p-p
R
OUT
= 100
Note that the output impedance of the AD9777 DAC itself is
greater than 100 k
and typically has no effect on the imped-
ance of the equivalent output circuit.
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
AD9777-EB 制造商:Analog Devices 功能描述:Evaluation Board For DAC, 16-Bit, 160MSPS 2/4/8 Interpolating Dual TxDAC+ D/A Converter 制造商:Analog Devices 功能描述:16BIT 160 MSPS DUAL TXDAC+ D/A CONVERTER - Bulk 制造商:Rochester Electronics LLC 功能描述:16BIT 160 MSPS DUAL TXDAC+ D/A CONVERTER - Bulk
AD9777-EBZ 功能描述:BOARD EVALUATION FOR AD9777 RoHS:是 類別:編程器，開(kāi)發(fā)系統(tǒng) >> 評(píng)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(shí)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
AD9778 制造商:AD 制造商全稱:Analog Devices 功能描述:400 MHz to 6 GHz Broadband Quadrature Modulator
AD9778A 制造商:AD 制造商全稱:Analog Devices 功能描述:Dual, 12-/14-/16-Bit,1 GSPS Digital-to-Analog Converters
AD9778ABSVZ 功能描述:DAC 14BIT 1.0GSPS 100-TQFP RoHS:是 類別:集成電路 (IC) >> 數(shù)據(jù)采集 - 數(shù)模轉(zhuǎn)換器 系列:- 標(biāo)準(zhǔn)包裝:1 系列:- 設(shè)置時(shí)間:4.5µs 位數(shù):12 數(shù)據(jù)接口:串行，SPI? 轉(zhuǎn)換器數(shù)目:1 電壓電源:單電源 功率耗散（最大）:- 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:8-SOIC（0.154"，3.90mm 寬） 供應(yīng)商設(shè)備封裝:8-SOICN 包裝:剪切帶 (CT) 輸出數(shù)目和類型:1 電壓，單極；1 電壓，雙極 采樣率（每秒）:* 其它名稱:MCP4921T-E/SNCTMCP4921T-E/SNRCTMCP4921T-E/SNRCT-ND
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