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參數資料
| 型號： | AD9709AST |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | DAC |
| 英文描述： | RES 0.01 OHM MAX 25 AMP AXIAL |
| 中文描述： | PARALLEL, 8 BITS INPUT LOADING, 0.035 us SETTLING TIME, 8-BIT DAC, PQFP48 |
| 封裝： | PLASTIC, LQFP-48 |
| 文件頁數： | 10/27頁 |
| 文件大小： | 466K |
| 代理商： | AD9709AST |
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REV. 0
AD9709
–10–
REFERENCE CONTROL AMPLIFIER
Both of the DACs in the AD9709 contain a control amplifier
that is used to regulate the full-scale output current, I
OUTFS
. The
control amplifier is configured as a V-I converter as shown in
Figure 21, so that its current output, I
REF
, is determined by the
ratio of the V
REFIO
and an external resistor, R
SET
, as stated in
Equation 4. I
REF
is copied to the segmented current sources with
the proper scale factor to set I
OUTFS
as stated in Equation 3.
+1.2V
REF
AVDD
GAINCTRL
CURRENT
SOURCE
ARRAY
REFIO
FSADJ
2k
0.1 F
ADDITIONAL
EXTERNAL
LOAD
OPTIONAL
EXTERNAL
REFERENCE
BUFFER
AD9709
REFERENCE
SECTION
I
REF
ACOM
Figure 21. Internal Reference Configuration
+1.2V
REF
AVDD
GAINCTRL
CURRENT
SOURCE
ARRAY
REFIO
FSADJ
2k
AD9709
REFERENCE
SECTION
I
REF
ACOM
AVDD
EXTERNAL
REFERENCE
Figure 22. External Reference Configuration
The control amplifier allows a wide (10:1) adjustment span of
I
OUTFS
from 2 mA to 20 mA by setting I
REF
between 62.5
μ
A
and 625
μ
A. The wide adjustment range of I
OUTFS
provides
several benefits. The first relates directly to the power dissipa-
tion of the AD9709, which is proportional to I
OUTFS
(refer to the
Power Dissipation section). The second relates to the 20 dB
adjustment, which is useful for system gain control purposes.
The small signal bandwidth of the reference control amplifier
is approximately 500 kHz and can be used for low frequency,
small signal multiplying applications.
DAC TRANSFER FUNCTION
Both DACs in the AD9709 provide complementary current out-
puts, I
OUTA
and I
OUTB
. I
OUTA
will provide a near full-scale current
output, I
OUTFS
, when all bits are high (i.e., DAC CODE = 1023)
while I
OUTB
, the complementary output, provides no current. The
current output appearing at I
OUTA
and I
OUTB
is a function of both
the input code and I
OUTFS
and can be expressed as:
I
OUTA
= (
DAC CODE
/256)
×
I
OUTFS
I
OUTB
= (255 –
DAC CODE
)/256
×
I
OUTFS
where
DAC CODE
= 0 to 255 (i.e., Decimal Representation).
As mentioned previously,
I
OUTFS
is a function of the reference
current I
REF
, which is nominally set by a reference voltage, V
REFIO
and external resistor R
SET
. It can be expressed as:
I
OUTFS
= 32
×
I
REF
where
I
REF
=
V
REFIO
/
R
SET
(1)
(2)
(3)
(4)
The two current outputs will typically drive a resistive load
directly or via a transformer. If dc coupling is required, I
OUTA
and I
OUTB
should be directly connected to matching resistive
loads, R
LOAD
, that are tied to analog common, ACOM. Note,
R
LOAD
may represent the equivalent load resistance seen by
I
OUTA
or I
OUTB
as would be the case in a doubly terminated 50
or 75
cable. The single-ended voltage output appearing at the
I
OUTA
and I
OUTB
nodes is simply :
V
OUTA
=
I
OUTA
×
R
LOAD
V
OUTB
=
I
OUTB
×
R
LOAD
Note the full-scale value of V
OUTA
and V
OUTB
should not exceed
the specified output compliance range to maintain specified
distortion and linearity performance.
V
DIFF
= (
I
OUTA
– I
OUTB
)
×
R
LOAD
Substituting the values of I
OUTA
, I
OUTB
and I
REF
; V
DIFF
can be
expressed as:
V
DIFF
= {(2
×
DAC CODE
– 255)/256}
×
(32
×
R
LOAD
/
R
SET
)
×
V
REFIO
These last two equations highlight some of the advantages of
operating the AD9709 differentially. First, the differential
operation will help cancel common-mode error sources associ-
ated with I
OUTA
and I
OUTB
such as noise, distortion and dc
offsets. Second, the differential code dependent current and
subsequent voltage, V
DIFF
, is twice the value of the single-ended
voltage output (i.e., V
OUTA
or V
OUTB
), thus providing twice the
signal power to the load.
Note, the gain drift temperature performance for a single-ended
(V
OUTA
and V
OUTB
) or differential output (V
DIFF
) of the AD9709
can be enhanced by selecting temperature tracking resistors for
R
LOAD
and R
SET
due to their ratiometric relationship as shown
in Equation 8.
(5)
(6)
(7)
(8)
ANALOG OUTPUTS
The complementary current outputs in each DAC, I
OUTA
and
I
OUTB
, may be configured for single-ended or differential opera-
tion. I
OUTA
and I
OUTB
can be converted into complementary
single-ended voltage outputs, V
OUTA
and V
OUTB
, via a load
resistor, R
LOAD
, as described in the DAC Transfer Function
section by Equations 5 through 8. The differential voltage, V
DIFF
,
existing between V
OUTA
and V
OUTB
can also be converted to a
single-ended voltage via a transformer or differential amplifier
configuration. The ac performance of the AD9709 is optimum
and specified using a differential transformer coupled output in
which the voltage swing at I
OUTA
and I
OUTB
is limited to
±
0.5 V.
If a single-ended unipolar output is desirable, I
OUTA
should be
selected.
The distortion and noise performance of the AD9709 can be
enhanced when it is configured for differential operation. The
common-mode error sources of both I
OUTA
and I
OUTB
can be
significantly reduced by the common-mode rejection of a
transformer or differential amplifier. These common-mode error
sources include even-order distortion products and noise. The
enhancement in distortion performance becomes more signifi-
cant as the frequency content of the reconstructed waveform
increases. This is due to the first order cancellation of various
dynamic common-mode distortion mechanisms, digital feed-
through and noise.
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相關代理商/技術參數 |
參數描述 |
|---|---|
| AD9709ASTRL | 制造商:Analog Devices 功能描述:DAC 2-CH Segment 8-bit 48-Pin LQFP T/R 制造商:Rochester Electronics LLC 功能描述:8-BIT 125 MSPS DUAL TXDAC+ D/A CONVERTER - Tape and Reel |
| AD9709ASTZ | 功能描述:IC DAC 8BIT DUAL 125MSPS 48-LQFP RoHS:是 類別:集成電路 (IC) >> 數據采集 - 數模轉換器 系列:TxDAC+® 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:50 系列:- 設置時間:4µs 位數:12 數據接口:串行 轉換器數目:2 電壓電源:單電源 功率耗散（最大）:- 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:8-TSSOP，8-MSOP（0.118"，3.00mm 寬） 供應商設備封裝:8-uMAX 包裝:管件 輸出數目和類型:2 電壓，單極 采樣率（每秒）:* 產品目錄頁面:1398 (CN2011-ZH PDF) |
| AD9709ASTZ1 | 制造商:AD 制造商全稱:Analog Devices 功能描述:8-Bit, 125 MSPS, Dual TxDAC Digital-to-Analog Converter |
| AD9709ASTZKL1 | 制造商:Rochester Electronics LLC 功能描述: 制造商:Analog Devices 功能描述: |
| AD9709ASTZRL | 功能描述:IC DAC 8BIT DUAL 125MSPS 48LQFP RoHS:是 類別:集成電路 (IC) >> 數據采集 - 數模轉換器 系列:TxDAC+® 產品培訓模塊:LTC263x 12-, 10-, and 8-Bit VOUT DAC Family 特色產品:LTC2636 - Octal 12-/10-/8-Bit SPI VOUT DACs with 10ppm/°C Reference 標準包裝:91 系列:- 設置時間:4µs 位數:10 數據接口:MICROWIRE?，串行，SPI? 轉換器數目:8 電壓電源:單電源 功率耗散（最大）:2.7mW 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:14-WFDFN 裸露焊盤 供應商設備封裝:14-DFN-EP（4x3） 包裝:管件 輸出數目和類型:8 電壓，單極 采樣率（每秒）:* |
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