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参数资料
| 型号： | AD9709-EBZ |
| 厂商： | Analog Devices Inc |
| 文件页数： | 6/32页 |
| 文件大小： | 0K |
| 描述： | BOARD EVAL FOR AD9709 |
| 产品培训模块： | DAC Architectures |
| 标准包装： | 1 |
| 系列： | TxDAC® |
| DAC 的数量： | 2 |
| 位数： | 8 |
| 采样率（每秒）： | 125M |
| 数据接口： | 并联 |
| 设置时间： | 35ns |
| DAC 型： | 电流 |
| 工作温度： | -40°C ~ 85°C |
| 已供物品： | 板 |
| 已用 IC / 零件： | AD9709 |
| 相关产品： | AD9709ASTZRL-ND - IC DAC 8BIT DUAL 125MSPS 48LQFP AD9709ASTZ-ND - IC DAC 8BIT DUAL 125MSPS 48-LQFP |
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AD9709
Rev. B | Page 14 of 32
DAC TRANSFER FUNCTION
Both DACs in the AD9709 provide complementary current out-
puts, IOUTA and IOUTB. IOUTA provides a near full-scale current
output, IOUTFS, when all bits are high (that is, DAC CODE = 256)
while IOUTB, the complementary output, provides no current.
The current output appearing at IOUTA and IOUTB is a function of
both the input code and IOUTFS and can be expressed as
IOUTA = (DAC CODE/256) × IOUTFS
(1)
IOUTB = (255 DAC CODE)/256 × IOUTFS
(2)
where DAC CODE = 0 to 255 (that is, decimal representation).
IOUTFS is a function of the reference current (IREF), which is
nominally set by a reference voltage (VREFIO) and an external
resistor (RSET). It can be expressed as
IOUTFS = 32 × IREF
(3)
where
IREF = VREFIO/RSET
(4)
The two current outputs typically drive a resistive load directly
or via a transformer. If dc coupling is required, IOUTA and IOUTB
should be connected directly to matching resistive loads, RLOAD,
that are tied to the analog common, ACOM. Note that RLOAD
can represent the equivalent load resistance seen by IOUTA or
IOUTB, as would be the case in a doubly terminated 50 Ω or 75 Ω
cable. The single-ended voltage output appearing at the IOUTA
and IOUTB nodes is
VOUTA = IOUTA × RLOAD
(5)
VOUTB = IOUTB × RLOAD
(6)
Note the full-scale value of VOUTA and VOUTB must not exceed the
specified output compliance range to maintain the specified
distortion and linearity performance.
VDIFF = (IOUTA IOUTB) × RLOAD
(7)
Equation 7 highlights some of the advantages of operating the
AD9709 differentially. First, the differential operation helps cancel
common-mode error sources associated with IOUTA and IOUTB,
such as noise, distortion, and dc offsets. Second, the differential
code-dependent current and subsequent voltage, VDIFF, is twice
the value of the single-ended voltage output (that is, VOUTA or
VOUTB), thus providing twice the signal power to the load.
Note that the gain drift temperature performance for a single-
ended (VOUTA and VOUTB) or differential output (VDIFF) of the
AD9709 can be enhanced by selecting temperature tracking
resistors for RLOAD and RSET due to their ratiometric relationship.
ANALOG OUTPUTS
The complementary current outputs, IOUTA and IOUTB, in each
DAC can be configured for single-ended or differential
operation. IOUTA and IOUTB can be converted into complementary
single-ended voltage outputs, VOUTA and VOUTB, via a load
resistor, RLOAD, as described in Equation 5 through Equation 7.
The differential voltage, VDIFF, existing between VOUTA and VOUTB
can 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 IOUTA
and IOUTB is limited to ±0.5 V. If a single-ended unipolar output
is desirable, IOUTA 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 IOUTA and IOUTB 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
significant 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
feedthrough, and noise.
Performing a differential-to-single-ended conversion via a
transformer also provides the ability to deliver twice the
reconstructed signal power to the load (that is, assuming no
source termination). Because the output currents of IOUTA and
IOUTB are complementary, they become additive when processed
differentially. A properly selected transformer allows the AD9709
to provide the required power and voltage levels to different loads.
The output impedance of IOUTA and IOUTB is determined by the
equivalent parallel combination of the PMOS switches
associated with the current sources and is typically 100 kΩ in
parallel with 5 pF. It is also slightly dependent on the output
voltage (that is, VOUTA and VOUTB) due to the nature of a PMOS
device. As a result, maintaining IOUTA and/or IOUTB at a virtual
ground via an I-V op amp configuration results in the optimum
dc linearity. Note that the INL/DNL specifications for the
AD9709 are measured with IOUTA maintained at a virtual ground
via an op amp.
IOUTA and IOUTB also have a negative and positive voltage
compliance range that must be adhered to in order to achieve
optimum performance. The negative output compliance range
of 1.0 V is set by the breakdown limits of the CMOS process.
Operation beyond this maximum limit may result in a
breakdown of the output stage and affect the reliability of the
AD9709.
The positive output compliance range is slightly dependent on
the full-scale output current, IOUTFS. When IOUTFS is decreased
from 20 mA to 2 mA, the positive output compliance range
degrades slightly from its nominal 1.25 V to 1.00 V. The optimum
distortion performance for a single-ended or differential output
is achieved when the maximum full-scale signal at IOUTA and IOUTB
does not exceed 0.5 V. Applications requiring the AD9709 output
(that is, VOUTA and/or VOUTB) to extend its output compliance range
should size RLOAD accordingly. Operation beyond this compliance
range adversely affects the linearity performance of the AD9709
and subsequently degrade its distortion performance.
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相关代理商/技术参数 |
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|---|---|
| AD9709-EBZ1 | 制造商:AD 制造商全称:Analog Devices 功能描述:8-Bit, 125 MSPS, Dual TxDAC Digital-to-Analog Converter |
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