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| 型号： | AD9838ACPZ-RL |
| 厂商： | Analog Devices Inc |
| 文件页数： | 7/32页 |
| 文件大小： | 0K |
| 描述： | IC DDS 16MHZ LOW PWR 20LFCSP |
| 产品培训模块： | Direct Digital Synthesis Tutorial Series (1 of 7): Introduction Direct Digital Synthesizer Tutorial Series (7 of 7): DDS in Action Direct Digital Synthesis Tutorial Series (3 of 7): Angle to Amplitude Converter Direct Digital Synthesis Tutorial Series (6 of 7): SINC Envelope Correction Direct Digital Synthesis Tutorial Series (4 of 7): Digital-to-Analog Converter Direct Digital Synthesis Tutorial Series (2 of 7): The Accumulator |
| 标准包装： | 5,000 |
| 分辨率（位）： | 10 b |
| 主 fclk： | 5MHz |
| 电源电压： | 2.3 V ~ 5.5 V |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 20-WFQFN 裸露焊盘，CSP |
| 供应商设备封装： | 20-LFCSP-WQ（4x4） |
| 包装： | 带卷 (TR) |
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AD9838
Rev. A | Page 15 of 32
CIRCUIT DESCRIPTION
The AD9838 is a fully integrated direct digital synthesis (DDS)
chip. The chip requires one reference clock, one low precision
resistor, and eight decoupling capacitors to provide digitally
created sine waves up to 8 MHz. In addition to the generation
of this RF signal, the chip is fully capable of a broad range of
simple and complex modulation schemes. These modulation
schemes are fully implemented in the digital domain, allowing
accurate and simple realization of complex modulation algo-
rithms using DSP techniques.
The internal circuitry of the AD9838 consists of the following
main sections: a numerically controlled oscillator (NCO),
frequency and phase modulators, SIN ROM, a digital-to-analog
converter, a comparator, and a regulator.
NUMERICALLY CONTROLLED OSCILLATOR PLUS
PHASE MODULATOR
The AD9838 consists of two frequency select registers, a phase
accumulator, two phase offset registers, and a phase offset adder.
The main component of the NCO is a 28-bit phase accumulator.
Continuous time signals have a phase range of 0 to 2π. Outside
this range of numbers, the sinusoid functions repeat themselves
in a periodic manner. The digital implementation is no different.
The accumulator simply scales the range of phase numbers into
a multibit digital word. The phase accumulator in the AD9838
is implemented with 28 bits. Therefore, in the AD9838, 2π = 228.
Likewise, the ΔPhase term is scaled into this range of numbers:
0 < ΔPhase < 228 1
With these substitutions, Equation 3 becomes
f =
ΔPhase × fMCLK∕228
(4)
where 0 < ΔPhase < 228 1.
The input to the phase accumulator can be selected from either
the FREQ0 register or the FREQ1 register and is controlled by
the FSELECT pin or the FSEL bit in the control register. NCOs
inherently generate continuous phase signals, thus avoiding any
output discontinuity when switching between frequencies.
Following the NCO, a phase offset can be added to perform
phase modulation using the 12-bit phase registers. The contents
of one of these phase registers is added to the MSBs of the NCO.
The AD9838 has two phase registers; their resolution is 2π/4096.
SIN ROM
To make the output from the NCO useful, it must be converted
from phase information into a sinusoidal value. Because phase
information maps directly to amplitude, the SIN ROM uses the
digital phase information as an address to a lookup table and
converts the phase information into amplitude.
Although the NCO contains a 28-bit phase accumulator, the
output of the NCO is truncated to 12 bits. Using the full reso-
lution of the phase accumulator is impractical and unnecessary
because a lookup table of 228 entries would be required. It is only
necessary to have sufficient phase resolution such that the errors
due to truncation are smaller than the resolution of the 10-bit
DAC. Therefore, the SIN ROM must have two bits of phase
resolution more than the 10-bit DAC.
The SIN ROM is enabled using the OPBITEN and MODE bits
(Bit D5 and Bit D1) in the control register (see Table 19).
DIGITAL-TO-ANALOG CONVERTER (DAC)
The AD9838 includes a high impedance, current source, 10-bit
DAC capable of driving a wide range of loads. The full-scale
output current can be adjusted for optimum power and external
load requirements using a single external resistor (RSET).
The DAC can be configured for single-ended or differential
operation. The IOUT and IOUTB pins can be connected through
equal external resistors to AGND to develop complementary
output voltages. The load resistors can be of any value required,
as long as the full-scale voltage developed across them does not
exceed the output compliance range. Because full-scale current
is controlled by RSET, adjustments to RSET can balance changes
made to the load resistors.
COMPARATOR
The AD9838 can be used to generate synthesized digital clock
signals. This is accomplished by using the on-board self-biasing
comparator that converts the sinusoidal signal of the DAC to a
square wave. The output from the DAC can be filtered externally
before being applied to the comparator input. The comparator
reference voltage is the time average of the signal applied to VIN.
The comparator can accept signals in the range of approximately
100 mV p-p to 1 V p-p. The comparator input is ac-coupled;
therefore, to operate correctly as a zero-crossing detector, the
comparator requires a minimum input frequency of 3 MHz typ-
ical. The comparator output is a square wave with an amplitude
from 0 V to DVDD.
The AD9838 provides a sampled signal with its output follow-
ing Nyquist sampling theorem. Specifically, its output spectrum
contains the fundamental plus aliased signals (images) that occur
at multiples of the reference clock frequency and the selected
output frequency. A graphical representation of the sampled
spectrum, with aliased images, is shown in Figure 21.
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| AD9838ACPZ-RL7 | 功能描述:IC DDS 16MHZ LOW PWR 20LFCSP RoHS:是 类别:集成电路 (IC) >> 接口 - 直接数字合成 (DDS) 系列:- 产品变化通告:Product Discontinuance 27/Oct/2011 标准包装:2,500 系列:- 分辨率（位）:10 b 主 fclk:25MHz 调节字宽（位）:32 b 电源电压:2.97 V ~ 5.5 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:16-TSSOP（0.173"，4.40mm 宽） 供应商设备封装:16-TSSOP 包装:带卷 (TR) |
| AD9838BCPZ-RL | 功能描述:IC DDS 16MHZ LOW PWR 20LFCSP RoHS:是 类别:集成电路 (IC) >> 接口 - 直接数字合成 (DDS) 系列:- 产品变化通告:Product Discontinuance 27/Oct/2011 标准包装:2,500 系列:- 分辨率（位）:10 b 主 fclk:25MHz 调节字宽（位）:32 b 电源电压:2.97 V ~ 5.5 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:16-TSSOP（0.173"，4.40mm 宽） 供应商设备封装:16-TSSOP 包装:带卷 (TR) |
| AD9838BCPZ-RL7 | 功能描述:IC DDS 16MHZ LP 20LFCSP RoHS:是 类别:集成电路 (IC) >> 接口 - 直接数字合成 (DDS) 系列:- 产品变化通告:Product Discontinuance 27/Oct/2011 标准包装:2,500 系列:- 分辨率（位）:10 b 主 fclk:25MHz 调节字宽（位）:32 b 电源电压:2.97 V ~ 5.5 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:16-TSSOP（0.173"，4.40mm 宽） 供应商设备封装:16-TSSOP 包装:带卷 (TR) |
| AD9840 | 制造商:AD 制造商全称:Analog Devices 功能描述:Complete 10-Bit 40 MSPS CCD Signal Processor |
| AD9840A | 制造商:AD 制造商全称:Analog Devices 功能描述:Complete 10-Bit 40 MSPS CCD Signal Processor |
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