参数资料
型号: AD9760ARZ
厂商: Analog Devices Inc
文件页数: 3/23页
文件大小: 0K
描述: IC DAC 10BIT 125MSPS 28-SOIC
产品培训模块: Data Converter Fundamentals
DAC Architectures
标准包装: 27
系列: TxDAC®
设置时间: 35ns
位数: 10
转换器数目: 1
电压电源: 模拟和数字
功率耗散(最大): 175mW
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 28-SOIC(0.295",7.50mm 宽)
供应商设备封装: 28-SOIC
包装: 管件
输出数目和类型: 2 电流,单极;2 电流,双极
采样率(每秒): 125M
配用: AD9760-EBZ-ND - BOARD EVAL FOR AD9760
AD9760
–11–
REV. B
FUNCTIONAL DESCRIPTION
Figure 39 shows a simplified block diagram of the AD9760.
The AD9760 consists of a large PMOS current source array that
is capable of providing up to 20 mA of total current. The array
is divided into 31 equal currents that make up the 5 most sig-
nificant bits (MSBs). The next 4 bits or middle bits consist
of 15 equal current sources whose value is 1/16th of an MSB
current source. The remaining LSBs is a binary weighted frac-
tion of the middle-bits current sources. Implementing the
middle and lower bits with current sources, instead of an R-2R
ladder, enhances its dynamic performance for multitone or low
amplitude signals and helps maintain the DAC’s high output
impedance (i.e., >100 k
).
All of these current sources are switched to one or the other of
the two output nodes (i.e., IOUTA or IOUTB) via PMOS differen-
tial current switches. The switches are based on a new architec-
ture that drastically improves distortion performance. This new
switch architecture reduces various timing errors and provides
matching complementary drive signals to the inputs of the dif-
ferential current switches.
The analog and digital sections of the AD9760 have separate
power supply inputs (i.e., AVDD and DVDD) that can operate
independently over a 2.7 volt to 5.5 volt range. The digital
section, which is capable of operating up to a 125 MSPS clock
rate, consists of edge-triggered latches and segment decoding
logic circuitry. The analog section includes the PMOS current
sources, the associated differential switches, a 1.20 V bandgap
voltage reference and a reference control amplifier.
The full-scale output current is regulated by the reference con-
trol amplifier and can be set from 2 mA to 20 mA via an exter-
nal resistor, RSET. The external resistor, in combination with
both the reference control amplifier and voltage reference
VREFIO, sets the reference current IREF, which is mirrored over to
the segmented current sources with the proper scaling factor.
The full-scale current, IOUTFS, is thirty-two times the value of IREF.
DAC TRANSFER FUNCTION
The AD9760 provides complementary current outputs, IOUTA
and IOUTB. IOUTA will provide a near full-scale current output,
IOUTFS, when all bits are high (i.e., DAC CODE = 1023) 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/1024)
× IOUTFS
(1)
IOUTB = (1023 – DAC CODE)/1024
× IOUTFS
(2)
where DAC CODE = 0 to 1023 (i.e., Decimal Representation).
As mentioned previously, IOUTFS is a function of the reference
current IREF, which is nominally set by a reference voltage,
VREFIO and external resistor RSET. It can be expressed as:
IOUTFS = 32
× IREF
(3)
where IREF = VREFIO/RSET
(4)
The two current outputs will typically drive a resistive load
directly or via a transformer. If dc coupling is required, IOUTA
and IOUTB should be directly connected to matching resistive
loads, RLOAD, that are tied to analog common, ACOM. Note,
RLOAD may represent the equivalent load resistance seen by
IOUTA or IOUTB as would be the case in a doubly terminated
50
or 75 cable. The single-ended voltage output appearing
at the IOUTA and IOUTB nodes is simply:
VOUTA = IOUTA
× RLOAD
(5)
VOUTB = IOUTB
× RLOAD
(6)
Note the full-scale value of VOUTA and VOUTB should not exceed
the specified output compliance range to maintain specified
distortion and linearity performance.
DIGITAL DATA INPUTS (DB9–DB0)
50pF
COMP1
+1.20V REF
AVDD
ACOM
REFLO
COMP2
PMOS
CURRENT SOURCE
ARRAY
0.1 F
+5V
SEGMENTED SWITCHES
FOR DB9–DB1
LSB
SWITCH
REFIO
FS ADJ
DVDD
DCOM
CLOCK
+5V
RSET
2k
0.1 F
IOUTA
IOUTB
0.1 F
AD9760
SLEEP
LATCHES
IREF
VREFIO
CLOCK
IOUTB
IOUTA
RLOAD
50
VOUTB
VOUTA
RLOAD
50
VDIFF = VOUTA – VOUTB
Figure 39. Functional Block Diagram
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