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參數資料
| 型號： | AD9832 |
| 廠商： | Analog Devices, Inc. |
| 元件分類： | XO, clock |
| 英文描述： | CMOS Complete DDS |
| 中文描述： | 完整的CMOS的直接數字合成器 |
| 封裝： | TSSOP-16 |
| 文件頁數： | 10/16頁 |
| 文件大?。?/td> | 146K |
| 代理商： | AD9832 |
AD9832
–10–
REV. A
CIRCUIT DESCRIPTION
The AD9832 provides an exciting new level of integration for
the RF/Communications system designer. The AD9832 com-
bines the Numerical Controlled Oscillator (NCO), SINE Look-
Up Table, Frequency and Phase Modulators, and a Digital-to-
Analog Converter on a single integrated circuit.
The internal circuitry of the AD9832 consists of three main
sections. They are:
Numerical Controlled Oscillator (NCO) + Phase Modulator
SINE Look-Up Table
Digital-to-Analog Converter
The AD9832 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 12.5 MHz. In addition to the genera-
tion of this RF signal, the chip is fully capable of a broad range
of simple and complex modulation schemes. These modula-
tion schemes are fully implemented in the digital domain, allow-
ing accurate and simple realization of complex modulation
algorithms using DSP techniques.
THEORY OF OPERATION
Sine waves are typically thought of in terms of their magnitude
form a(t) = sin (
ω
t). However, these are nonlinear and not easy
to generate except through piecewise construction. On the other
hand, the angular information is linear in nature. That is, the
phase angle rotates through a fixed angle for each unit of time.
The angular rate depends on the frequency of the signal by the
traditional rate of
ω
= 2
π
f.
MAGNITUDE
PHASE
+1
0
–1
2
0
Figure 21. Sine Wave
Knowing that the phase of a sine wave is linear and given a
reference interval (clock period), the phase rotation for that
period can be determined.
Phase
=
ωδ
t
Solving for
ω
ω
=
Phase
/
δ
t = 2
π
f
Solving for
f
and substituting the reference clock frequency for
the reference period (1/f
MCLK
=
δ
t)
f
=
Phase
×
f
MCLK
/2
π
The AD9832 builds the output based on this simple equation. A
simple DDS chip can implement this equation with three major
subcircuits.
Numerical Controlled Oscillator + Phase Modulator
This consists of two frequency select registers, a phase accumu-
lator and four phase offset registers. The main component of the
NCO is a 32-bit phase accumulator that assembles the phase
component of the output signal. Continuous time signals have a
phase range of 0 to 2
π
. 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 AD9832 is implemented with 32
bits. Therefore, in the AD9832, 2
π
= 2
32
. Likewise, the
Phase
term is scaled into this range of numbers 0 <
Phase
< 2
32
– 1.
Making these substitutions into the equation above
f
=
Phase
×
f
MCLK
/2
32
where 0 <
Phase
< 2
32
.
The input to the phase accumulator (i.e., the phase step) can be
selected from either the FREQ0 Register or FREQ1 Register
and this is controlled by the FSELECT pin or the FSELECT
bit. 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 con-
tents of this register are added to the most significant bits of the
NCO. The AD9832 has four PHASE registers, the resolution of
these registers being 2
π
/4096.
Sine Look-Up Table (LUT)
To make the output useful, the signal must be converted from
phase information into a sinusoidal value. Since phase informa-
tion maps directly into amplitude, a ROM LUT converts the
phase information into amplitude. To do this, the digital phase
information is used to address a sine ROM LUT. Although the
NCO contains a 32-bit phase accumulator, the output of the
NCO is truncated to 12 bits. Using the full resolution of the
phase accumulator is impractical and unnecessary as this would
require a look-up table of 2
32
entries.
It is necessary only to have sufficient phase resolution in the
LUTs so the dc error of the output waveform is dominated by
the quantization error in the DAC. This requires the look-up
table to have two more bits of phase resolution than the 10-bit
DAC.
Digital-to-Analog Converter
The AD9832 includes a high impedance current source 10-bit
DAC, capable of driving a wide range of loads at different
speeds. Full-scale output current can be adjusted, for optimum
power and external load requirements, through the use of a
single external resistor (R
SET
).
The DAC is configured for single-ended operation. The load
resistor can be any value required, as long as the full-scale volt-
age developed across it does not exceed the voltage compliance
range. Since full-scale current is controlled by R
SET
, adjust-
ments to R
SET
can balance changes made to the load resistor.
However, if the DAC full-scale output current is significantly
less than 4 mA, the DAC’s linearity may degrade.
DSP and MPU Interfacing
The AD9832 has a serial interface, with 16 bits being loaded
during each write cycle. SCLK, SDATA and FSYNC are used
to load the word into the AD9832. When FSYNC is taken low,
the AD9832 is informed that a word is being written to the
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相關代理商/技術參數 |
參數描述 |
|---|---|
| AD9832_13 | 制造商:AD 制造商全稱:Analog Devices 功能描述:25 MHz Direct Digital Synthesizer, Waveform Generator |
| AD9832BRU | 功能描述:IC DDS DAC 10BIT 25MHZ 16-TSSOP RoHS:否 類別:集成電路 (IC) >> 接口 - 直接數字合成 (DDS) 系列:- 產品變化通告:Product Discontinuance 27/Oct/2011 標準包裝:2,500 系列:- 分辨率（位）:10 b 主 fclk:25MHz 調節字寬（位）:32 b 電源電壓:2.97 V ~ 5.5 V 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:16-TSSOP（0.173"，4.40mm 寬） 供應商設備封裝:16-TSSOP 包裝:帶卷 (TR) |
| AD9832BRU-REEL | 功能描述:IC DDS 10BIT 25MHZ CMOS 16-TSSOP RoHS:否 類別:集成電路 (IC) >> 接口 - 直接數字合成 (DDS) 系列:- 產品變化通告:Product Discontinuance 27/Oct/2011 標準包裝:2,500 系列:- 分辨率（位）:10 b 主 fclk:25MHz 調節字寬（位）:32 b 電源電壓:2.97 V ~ 5.5 V 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:16-TSSOP（0.173"，4.40mm 寬） 供應商設備封裝:16-TSSOP 包裝:帶卷 (TR) |
| AD9832BRU-REEL7 | 功能描述:IC DDS 10BIT 25MHZ CMOS 16-TSSOP RoHS:否 類別:集成電路 (IC) >> 接口 - 直接數字合成 (DDS) 系列:- 產品變化通告:Product Discontinuance 27/Oct/2011 標準包裝:2,500 系列:- 分辨率（位）:10 b 主 fclk:25MHz 調節字寬（位）:32 b 電源電壓:2.97 V ~ 5.5 V 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:16-TSSOP（0.173"，4.40mm 寬） 供應商設備封裝:16-TSSOP 包裝:帶卷 (TR) |
| AD9832BRUZ | 功能描述:IC DDS 10BIT 25MHZ CMOS 16-TSSOP RoHS:是 類別:集成電路 (IC) >> 接口 - 直接數字合成 (DDS) 系列:- 產品變化通告:Product Discontinuance 27/Oct/2011 標準包裝:2,500 系列:- 分辨率（位）:10 b 主 fclk:25MHz 調節字寬（位）:32 b 電源電壓:2.97 V ~ 5.5 V 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:16-TSSOP（0.173"，4.40mm 寬） 供應商設備封裝:16-TSSOP 包裝:帶卷 (TR) |
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