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參數資料
| 型號： | AD9854AST |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | XO, clock |
| 英文描述： | CMOS 300 MHz Quadrature Complete-DDS |
| 中文描述： | PLL FREQUENCY SYNTHESIZER, 200 MHz, PQFP80 |
| 封裝： | MS-026BEC, LQFP-80 |
| 文件頁數： | 19/44頁 |
| 文件大?。?/td> | 433K |
| 代理商： | AD9854AST |
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AD9854
–19–
REV. 0
F1
F2
0
F
MODE
TW1
TW2
FSK DATA
010 (RAMPED FSK)
F1
F2
000 (DEFAULT)
0
0
Figure 38. Ramped FSK Mode
Ramped FSK (Mode = 010)
A method of FSK whereby changes from F1 to F2 are not
instantaneous but, instead, are accomplished in a frequency
sweep or “ramped” fashion. The “ramped” notation implies
that the sweep is linear. While linear sweeping or frequency
ramping is easily and automatically accomplished, it is only one
of many possibilities. Other frequency transition schemes may
be implemented by changing the ramp rate and ramp step size
“on-the-fly,” in piecewise fashion.
Frequency ramping, whether linear or nonlinear, necessitates
that many intermediate frequencies between F1 and F2 will be
output in addition to the primary F1 and F2 frequencies. Figures
37 and 38 graphically depict the frequency versus time charac-
teristics of a linear ramped FSK signal.
The purpose of ramped FSK is to provide better bandwidth
containment than traditional FSK by replacing the instantaneous
frequency changes with more gradual, user-defined frequency
changes. The dwell time at F1 and F2 can be equal to or much
greater than the time spent at each intermediate frequency. The
user controls the dwell time at F1 and F2, the number of inter-
mediate frequencies and time spent at each frequency. Unlike
unramped FSK, ramped FSK requires the lowest frequency to be
loaded into F1 registers and the highest frequency into F2 registers.
Several registers must be programmed to instruct the DDS
regarding the resolution of intermediate frequency steps (48
bits) and the time spent at each step (20 bits). Furthermore, the
CLR ACC1 bit in the control register should be toggled (low-high-
low) prior to operation to assure that the frequency accumulator
is starting from an “all zeros” output condition. For piecewise,
nonlinear frequency transitions, it is necessary to reprogram the
registers
while
the frequency transition is in progress to affect the
desired response.
Parallel register addresses 1A–1C hex comprise the 20-bit “Ramp
Rate Clock” registers. This is a countdown counter that outputs
a single pulse whenever the count reaches zero. The counter
is activated any time a logic level change occurs on FSK input
Pin 29. This counter is run at the System Clock Rate, 300 MHz
maximum. The time period between each output pulse is given as
(N+
1
)
×
(SYSTEM CLOCK PERIOD)
where
N
is the 20-bit ramp rate clock value programmed by the
user. Allowable range of N is from 1 to (2
20
–1). The output of
this counter clocks the 48-bit Frequency Accumulator
shown
below in Figure 39. The Ramp Rate Clock determines the amount
of time spent at each intermediate frequency between F1 and F2.
The counter stops automatically when the destination frequency
is achieved. The “dwell time” spent at F1 and F2 is determined
by the duration that the FSK input, Pin 29, is held high or low
after the destination frequency has been reached.
FREQUENCY
TUNING
WORD 1
20-BIT
RAMP RATE
CLOCK
48-BIT DELTA-
FREQUENCY
WORD
FREQUENCY
ACCUMULATOR
PHASE
ACCUMULATOR
OUT
ADDER
FSK
(PIN 29)
SYSTEM
CLOCK
FREQUENCY
TUNING
WORD 2
Figure 39. Block Diagram of Ramped FSK Function
Parallel register addresses 10–15 hex comprise the 48-bit, straight
binary
,
“Delta Frequency Word” registers. This 48-bit word
is accumulated (added to the accumulator’s output) every time
it receives a clock pulse from the ramp rate counter. The output
of this accumulator is then added to or subtracted from the F1
or F2 frequency word, which is then fed to the input of the
48-bit
Phase Accumulator that forms the numerical phase steps for the
sine and cosine wave outputs. In this fashion, the output frequency
is ramped up and down in frequency, according to the logic-
state of Pin 29. The rate at which this happens is a function of
the 20-bit ramp rate clock. Once the destination frequency is
achieved, the ramp rate clock is stopped, which halts the frequency
accumulation process.
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相關代理商/技術參數 |
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|---|---|
| AD9854ASTZ | 功能描述:IC DDS QUADRATURE CMOS 80-LQFP 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(jié)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) |
| AD9854ASVZ | 制造商:Analog Devices 功能描述:CMOS 300 MSPS QUADRATURE COMPLETE DDS 制造商:Analog Devices 功能描述:CMOS 300 MSPS QUADRATURE COMPLETE DDS - Trays 制造商:Analog Devices 功能描述:SYNTHESIZER 制造商:Analog Devices 功能描述:Complete DDS Quadrature 300MSPS TQFP80 |
| AD9854PCB | 制造商:AD 制造商全稱:Analog Devices 功能描述:CMOS 300 MSPS Quadrature Complete DDS |
| AD9856 | 制造商:AD 制造商全稱:Analog Devices 功能描述:CMOS 200 MHz Quadrature Digital Upconverter |
| AD9856/PCB | 制造商:Analog Devices 功能描述:Evaluation Board For Digital Up Converter 56 Pin LFCSP Ep 制造商:Analog Devices 功能描述:DGTL UP CNVRTR 56LFCSP - Bulk |
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