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| 型號： | AD9547/PCBZ |
| 廠商： | Analog Devices Inc |
| 文件頁數(shù)： | 33/104頁 |
| 文件大?。?/td> | 0K |
| 描述： | BOARD EVALUATION FOR AD9547 |
| 設(shè)計資源： | AD9547 Schematic AD9574 BOM |
| 標準包裝： | 1 |
| 主要目的： | 計時，時鐘發(fā)生器 |
| 嵌入式： | 否 |
| 已用 IC / 零件： | AD9547 |
| 主要屬性： | 2 個差分式或 4 個單端輸入 |
| 次要屬性： | CMOS，LVPECL 和 LVDS 兼容 |
| 已供物品： | 板 |
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AD9547
Data Sheet
Rev. E | Page 34 of 104
phase error sample but, rather, its magnitude relative tothe phase
threshold value that determines whether to fill or drain. If more
filling is taking place than draining, the water level in the tub
eventually rises above the high water mark (+1024), which causes
the phase lock detector toindicate lock. If more draining is taking
place than filling, the water levelin the tubeventually falls below
the low water mark (1024), which causes the phase lock detector
to indicate unlock. The ability to specify the threshold level, fill
rate, and drain rate enables the user to tailor the operation of
the phase lock detector to the statistics of the timing jitter
associated with the input reference signal.
Note that when the AD9547 enters the free-run or holdover
mode, the DPLL phase lock detector indicates unlocked. Also,
when the AD9547 performs a reference switchover, the state of
the lock detector prior to the switch is preserved during the
transition period.
DPLLFrequencyLock Detector
The operation of the frequency lock detector is identical to that
of the phase lock detector. The only difference is that the fill or
drain decision is based on the period deviation between the
reference and feedback signals of the DPLL instead of the phase
error at the output of the PFD.
The frequency lock detector uses a 24-bit frequency threshold
register specified in units of picoseconds (ps). Thus, the fre-
quency threshold value extends from 0 μs to ±16.777215 μs.
It represents the magnitude of the difference in period between
the reference and feedback signals at the input to the DPLL. For
example, if the reference signal is 1.25 MHz and the feedback
signal is 1.38 MHz, the period difference is approximately 75.36 ns
(|1/1,250,000 1/1,380,000| ≈ 75.36 ns).
DIRECT DIGITAL SYNTHESIZER (DDS)
DDS Overview
One of the primary building blocks of the digital PLL is a direct
digital synthesizer (DDS). The DDS behaves like a sinusoidal
signal generator. The frequency of the sinusoid generated by the
DDS is determined by a frequency tuning word (FTW), which
is a digital (that is, numeric) value. Unlike an analog sinusoidal
generator, a DDS uses digital building blocks and operates as a
sampled system. Thus, it requires a sampling clock (fS) that serves
as the fundamental timing source of the DDS. The accumulator
behaves as a modulo-248 counter with a programmable step size
(FTW). A block diagram of the DDS appears in Figure 41.
The input to the DDS is the 48-bit FTW. The FTW serves as
a step size value. On each cycle of fS, the accumulator adds the
value of the FTW to the running total at its output. For example,
given that FTW = 5, the accumulator counts by fives, incre-
menting on each fS cycle. Over time, the accumulator reaches
the upper end of its capacity (248 in this case), at which point,
it rolls over but retains the excess. The average rate at which the
accumulator rolls over establishes the frequency of the output
sinusoid. The average rollover rate of the accumulator establishes
the output frequency (fDDS) of the DDS and is given by
S
DDS
f
FTW
f
=
48
2
Solving this equation for FTW yields
=
S
DDS
f
FTW
48
2
round
For example, given that fS = 1 GHz and fDDS = 155.52 MHz, then
FTW = 43,774,988,378,041 (0x27D028A1DFB9).
Note that the minimum DAC output frequency is 62.5 MHz;
therefore, normal operation requires an FTW that yields an
output frequency in excess of this lower bound.
DAC
(14-BIT)
PHASE
OFFSET
Q
D
fS
FREQUENCY
TUNING WORD
(FTW)
DAC+
DAC–
14
19
48
19
ANGLE TO
AMPLITUDE
CONVERSION
48
48-BIT ACCUMULATOR
16
08300-
018
Figure 41. DDS Block Diagram
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| AD9548/PCBZ | 功能描述:BOARD EVAL FOR AD9548 RoHS:是 類別:編程器，開發(fā)系統(tǒng) >> 評估演示板和套件 系列:- 標準包裝:1 系列:PSoC® 主要目的:電源管理，熱管理 嵌入式:- 已用 IC / 零件:- 主要屬性:- 次要屬性:- 已供物品:板，CD，電源 |
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