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参数资料
| 型号： | AD9549A/PCBZ |
| 厂商： | Analog Devices Inc |
| 文件页数： | 16/76页 |
| 文件大小： | 0K |
| 描述： | BOARD EVALUATION FOR AD9549A |
| 设计资源： | AD9549 Schematics AD9549 Gerber Files |
| 标准包装： | 1 |
| 主要目的： | 计时，时钟发生器 |
| 嵌入式： | 否 |
| 已用 IC / 零件： | AD9549A |
| 主要属性： | 8 kHz ~ 750 MHz 输入 |
| 次要属性： | 差分输出 |
| 已供物品： | 板 |
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AD9549
Rev. D | Page 23 of 76
The three coefficients are implemented as digital elements,
necessitating quantized values. Determination of the
programmed coefficient values in this context follows.
The quantized α coefficient is composed of three factors, where
α0, α1, and α2 are the programmed values for the α coefficient.
( )( )2
1
α
0
QUANTIZED
α
=
2
2048
The boundary values for each are 0 ≤ α0 ≤ 4095, 0 ≤ α1 ≤ 22,
and 0 ≤ α2 ≤ 7. The optimal values of α0, α1, and α2 are
=
4095
2048
log
ceil
,
22
min
,
0
max
2
α
α1
α
+
α
=
11
4095
log
floor
,
7
min
,
0
max
2
1
2
α
(
)
{
}
[
]
11
2
round
,
4095
min
,
0
max
+
×
=
1
2
α
0
α
The magnitude of the quantized β coefficient is composed of
two factors
( )
(
))
15
(
2
+
=
1
β
0
QUANTIZED
β
where β0 and β1 are the programmed values for the β coefficient.
The boundary values for each are 0 ≤ β0 ≤ 4095 and 0 ≤ β1 ≤ 7.
The optimal values of β0 and β1 are
=
15
4095
log
floor
,
7
min
,
0
max
2
β
β1
(
)
{
}
[
]
15
2
round
,
4095
min
,
0
max
+
×
=
1
β
0
β
The magnitude of the quantized γ coefficient is composed of
two factors.
( )
(
))
15
(
2
+
=
1
γ
0
QUANTIZED
γ
where γ0 and γ1 are the programmed values for the γ coefficient.
The boundary values for each are 0 ≤ γ0 ≤ 4095 and 0 ≤ γ1 ≤ 7.
The optimal values of γ0 and γ1 are
γ
=
γ
15
4095
log
floor
,
7
min
,
0
max
2
1
(
)
{
}
[
]
15
2
round
,
4095
min
,
0
max
+
γ
×
γ
=
γ
1
0
The min(), max(), floor(), ceil() and round() functions are
defined as follows:
The function min(x1, x2, … xn) chooses the smallest value
in the list of arguments.
The function max(x1, x2, … xn) chooses the largest value in
the list of arguments.
The function ceil(x) increases x to the next higher integer
if x is not an integer; otherwise, x is unchanged.
The function floor(x) reduces x to the next lower integer
if x is not an integer; otherwise, x is unchanged.
The function round(x) rounds x to the nearest integer.
To demonstrate the wide programmable range of the loop filter
bandwidth, consider the following design example. The system
clock frequency (fS) is 1 GHz, the input reference frequency (fR)
is 19.44 MHz, the DDS output frequency (fDDS) is 155.52 MHz,
and the required phase margin (Φ) is 45°. fR is within the nominal
bandwidth of the phase detector (25 MHz), and fDDS/fR is an integer
(8), so the prescaler is not required. Therefore, R = 1 and S = 8 can
be used for the feedforward and feedback dividers, respectively.
Note that if fDDS/fR is a noninteger, then R and S must be chosen
such that S/R = fDDS/fR with S and R both constrained to integer
values. For example, if fR = 10 MHz and fDDS = 155.52 MHz,
then the optimal choice for S and R is 1944 and 125, respectively.
The open-loop bandwidth range under the defined conditions
spans 9.5 Hz to 257.5 kHz. The wide dynamic range of the loop
filter coefficients allows for programming of any open-loop
bandwidth within this range under these conditions. The
resulting closed-loop bandwidth range under the same
conditions is approximately 12 Hz to 359 kHz.
The resulting loop filter coefficients for the upper loop bandwidth,
along with the necessary programming values, are shown as
follows:
α = 4322509.4784981
α0 = 2111 (0x83F)
α1 = 22 (0x16)
α2 = 0 (0x00)
β = 0.10354689386232
β0 = 3393 (0xD41)
β1 = 0 (0x00)
γ0 = 4095 (0xFFF)
γ = 0.12499215775201
γ1 = 0 (0x00)
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