参数资料
| 型号： | AD9774ASZRL |
| 厂商： | Analog Devices Inc |
| 文件页数： | 3/24页 |
| 文件大小： | 0K |
| 描述： | IC DAC 14BIT 32MSPS 44MQFP |
| 产品变化通告： | Product Discontinuance 27/Oct/2011 |
| 标准包装： | 800 |
| 系列： | TxDAC+® |
| 设置时间： | 35ns |
| 位数： | 14 |
| 数据接口： | 并联 |
| 转换器数目： | 1 |
| 电压电源： | 模拟和数字 |
| 功率耗散（最大）： | 1.13W |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 44-QFP |
| 供应商设备封装： | 44-MQFP（10x10） |
| 包装： | 带卷 (TR) |
| 输出数目和类型： | 2 电流，单极；2 电流，双极 |
| 采样率（每秒）： | 32M |
AD9774
–11–
REV. B
PLL CLOCK MULTIPLIER OPERATION
The Phase Lock Loop (PLL) Clock Multiplier is intrinsic to the
operation of the AD9774 in that it produces the necessary inter-
nally synchronized 1
×, 2× and 4× clocks for the edge triggered
latches, interpolation filters and DACs. Figure 24 shows a func-
tional block diagram of the PLL Clock Multiplier, which con-
sists of a phase detector, a charge pump, a voltage controlled
oscillator (VCO), a divide-by-N circuit and some control inputs/
outputs. It produces the required internal clocks for the AD9774
by using one of two possible externally applied reference clock
sources applied to either CLKIN or CLK4
×IN. PLLENABLE
and VCO IN/EXT are active HIGH control inputs used to
enable the charge pump and VCO respectively.
To maintain optimum noise and distortion performance,
PLLVDD and DVDD should be set to similar voltage levels. If
a separate supply cannot be provided for PLLVDD, PLLVDD
can be tied to DVDD using an LC filter network similar to that
shown in Figure 41.
Many applications will select a reference clock operating at the
data input rate as shown in Figure 24. In this case, the external
clock source is applied to CLKIN and the PLL Clock Multiplier
is fully enabled by tying PLLENABLE and VCO IN/EXT to
PLLVDD. Note, CLKIN must adhere to the timing require-
ments shown in Figure 1. A 1.5 k
resistor and 0.01 F ceramic
capacitor connected in series from LPF to PLLVDD are re-
quired to optimize the phase noise vs. settling/acquisition time
characteristics of the PLL. PLLLOCK is a control output, ac-
tive HIGH, which may be monitored upon system power-up to
indicate that the PLL is successfully “locked” to CLKIN. Note,
applications employing multiple AD9774 devices will benefit
from the PLL Clock Multiplier’s ability to ensure precise simul-
taneous updating/phase synchronization of these devices when
driven by the same input clock source.
PLLDIVIDE is used to preset the “lock-in” range of the PLL. It
should be tied to PLLCOM if CLKIN is greater than 10 MHz
and to PLLVDD if CLKIN is between 5.5 MHz and 10 MHz.
For operation below 5.5 MHz (i.e., input data rates less than
5.5 MSPS), the internal charge pump and VCO should be
disabled by tying PLLENABLE and VCO IN/EXT LOW. In
this case, the user MUST supply a system clock operating at 4
×
the input data rate as discussed below.
CONNECT TO
PLLCOM
CONNECT TO
PLLVDD
PLL
DIVIDE
CLK
IN/OUT
PLLLOCK
PLL
ENABLE
LPF
1.5k
0.01 F
+2.7 TO
+5.5 VD
+2.7 TO +5.5 VD
PLL
VDD
PLL
COM
VCO
IN/EXT
DVDD
CLK
4 IN
DCOM
DIVIDE-
BY-N
8
4
2
1
VCO
CHARGE
PUMP
PHASE
DETECTOR
AD9774
Figure 24. Clock Multiplier with PLL Enabled
There are two cases in which a user may consider or be required
to disable the internal PLL Clock Multiplier and supply the
AD9774 with an external 4
× system clock. Applications already
containing a system clock operating at four (i.e., 4
×) the input
data rate may consider using it as the master clock source. Ap-
plications with input data rates less than 5.5 MSPS
must use a
master 4
× clock.
In any of these cases, the clock source is applied to CLK4
×IN
and the PLL is partially disabled by typing PLLENABLE and
VCO IN/EXT to PLLCOM as shown in Figure 25. LPF may
remain open since this portion of the PLL circuitry is disabled.
The divide-by-N circuit still remains enabled providing a 1
× or
2
× internal clock at CLOCK IN/OUT depending on the state of
PLLDIVIDE. Since the digital input data is latched into the
AD9774 on the rising edge of the 1
× clock, PLLDIVIDE should
be tied to PLLCOM such that the 1
× clock appears as an output
at CLOCK IN/OUT. The input data should be stable 5 ns (i.e.,
data set-up) before the rising edge of the 1
× clock appearing at
CLOCK IN/OUT and remain stable for 1 ns after the rising
edge (i.e., data hold) to ensure proper latching. Note, the rising
edge of the 1
× clock occurs approximately 9 ns to 15 ns relative
to the falling edge of the CLK4
× input. If a data timing issue
exists between the AD9774 and its external driver device, the
CLK4
× input can be inverted via an external gate to ensure
proper set-up and hold time.
PLL
DIVIDE
PLLLOCK
PLL
ENABLE
LPF
+2.7 TO +5.5 VD
PLL
VDD
PLL
COM
VCO
IN/EXT
DVDD
CLK
4 IN
DCOM
DIVIDE-
BY-N
8
4
2
1
VCO
CHARGE
PUMP
PHASE
DETECTOR
AD9774
CLK
IN/OUT
+2.7 TO +5.5 VD
Figure 25. Clock Divider with PLL Disabled
DAC OPERATION
The 14-bit DAC along with the 1.2 V reference and reference
control amplifier is shown in Figure 26. The DAC consists of a
large PMOS current source array capable of providing up to
20 mA of full-scale current, IOUTFS. The array is divided into 31
equal currents which make up the five most significant bits
(MSBs). The next four bits or middle bits consist of 15 equal
current sources whose values are 1/16th of an MSB current
source. The remaining LSBs are binary weighted fractions of the
middle-bits current sources. All of these current sources are
switched to one or the other of two output nodes (i.e., IOUTA
or IOUTB) via PMOS differential current switches. Implement-
ing 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
).
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相关代理商/技术参数 |
参数描述 |
|---|---|
| AD9774EB | 制造商:AD 制造商全称:Analog Devices 功能描述:14-Bit, 32 MSPS TxDAC⑩ with 4x Interpolation Filters |
| AD9774-EB | 制造商:Analog Devices 功能描述: |
| AD9774-EBZ | 制造商:Analog Devices 功能描述:14-BIT 32 MSPS TXDAC W/4X INTERPOLATION - Bulk |
| AD9775 | 制造商:AD 制造商全称:Analog Devices 功能描述:14-Bit, 160 MSPS 2X/4X/8X Interpolating Dual TxDAC+ D/A Converter |
| AD9775BSV | 制造商:Analog Devices 功能描述:DAC 2-CH R-2R 14-bit 80-Pin TQFP EP 制造商:Rochester Electronics LLC 功能描述:14BIT 160 MSPS DUAL TXDAC+ D/A CONVERTER - Bulk 制造商:Analog Devices 功能描述:IC 14-BIT DAC |
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