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| 型号： | LTC6945IUFD#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 11/28页 |
| 文件大小： | 0K |
| 描述： | IC SYNTHESIZER INTEGER N 28QFN |
| 软件下载： | PLLWizard™ PLLWizard™, with .NET 2.0 installer |
| 标准包装： | 73 |
| 类型： | * |
| PLL： | 是 |
| 输入： | 时钟 |
| 输出： | 时钟 |
| 电路数： | 1 |
| 比率 - 输入:输出： | 1:1 |
| 差分 - 输入:输出： | 是/是 |
| 频率 - 最大： | 6GHz |
| 除法器/乘法器： | 是/无 |
| 电源电压： | 3.15 V ~ 5.25 V |
| 工作温度： | -40°C ~ 105°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 28-WFQFN 裸露焊盘 |
| 供应商设备封装： | 28-QFN（4x5） |
| 包装： | 管件 |
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LTC6945
19
6945f
APPLICATIONS INFORMATION
4. Select loop filter components CI and CP based on BW
and RZ. A reliable loop can be achieved by using the
following equations for the loop capacitors (in Farads):
C
I =
3.5
2
π BW R
Z
(7)
C
P =
1
7
π BW R
Z
(8)
LOOP FILTERS USING AN OPAMP
Some VCO tune voltage ranges are greater than the
LTC6945’s charge pump voltage range. An active loop filter
using an op amp can increase the tuning voltage range.
To maintain the LTC6945’s high performance, care must
be given to picking an appropriate op amp.
The op amp input common mode voltage should be biased
within the LTC6945 charge pump’s voltage range, while
its output voltage should achieve the VCO tuning range.
See Figure 16 for an example op amp loop filter.
The op amp’s input bias current is supplied by the charge
pump; minimizing this current keeps spurs related to fPFD
low. The input bias current should be less than the charge
pump leakage (found in the Electrical Characteristics sec-
tion) to avoid increasing spurious products.
Op amp noise sources are highpass filtered by the PLL
loop filter and should be kept at a minimum, as their ef-
fect raises the total system phase noise beginning near
the loop bandwidth. Choose a low noise op amp whose
input-referred voltage noise is less than the thermal noise
of RZ. Additionally, the gain bandwidth of the op amp
should be at least 15 times the loop bandwidth to limit
phase margin degradation. The LT1678 is an op amp that
works very well in most applications.
An additional R-C lowpass filter (formed by RP2 and CP2
in Figure 16) connected at the input of the VCO will limit
the op amp noise sources. The bandwidth of this filter
should be placed approximately 15 to 20 times the PLL
loop bandwidth to limit loop phase margin degradation.
RP2 should be small (preferably much less than RZ) to
minimize its noise impact on the loop. However, picking
too small of a value can make the op amp unstable as it
has to drive the capacitor in this filter.
DESIGN AND PROGRAMMING EXAMPLE
This programming example uses the DC1649. Assume
the following parameters of interest :
fREF = 100MHz at 7dBm into 50Ω
fSTEP = 250kHz
fVCO = 902MHz to 928MHz
KVCO = 15MHz/V to 21.6MHz/V
fRF = 914MHz
Determining Divider Values
Following the Loop Filter Design algorithm, first determine
all the divider values. Using Equations 2, 3, 4 and 5, cal-
culate the following values:
O = 1
R = 100MHz/250kHz = 400
fPFD = 250kHz
N = 914MHz/250kHz = 3656
Figure 16. Op Amp Loop Filter
CP
LOOP FILTER
LF(s)
CI
CP2
KVCO
6945 F16
47μF
CP
ICP
VCO±
(fVCO)
VCP
+/2
5k
VCP
+
LTC6945
RZ
RP2
–
+
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相关代理商/技术参数 |
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| LTC6946-1 | 制造商:LINER 制造商全称:Linear Technology 功能描述:30MHz to 1.4GHz IQ Demodulator |
| LTC6946-2 | 制造商:LINER 制造商全称:Linear Technology 功能描述:30MHz to 1.4GHz IQ Demodulator |
| LTC6946-3 | 制造商:LINER 制造商全称:Linear Technology 功能描述:30MHz to 1.4GHz IQ Demodulator |
| LTC6946IUFD-1#PBF | 功能描述:IC INTEGER-N PLL W/VCO 28-QFN RoHS:是 类别:集成电路 (IC) >> 时钟/计时 - 时钟发生器，PLL，频率合成器 系列:- 标准包装:2,000 系列:- 类型:PLL 频率合成器 PLL:是 输入:晶体 输出:时钟 电路数:1 比率 - 输入:输出:1:1 差分 - 输入:输出:无/无 频率 - 最大:1GHz 除法器/乘法器:是/无 电源电压:4.5 V ~ 5.5 V 工作温度:-20°C ~ 85°C 安装类型:表面贴装 封装/外壳:16-LSSOP（0.175"，4.40mm 宽） 供应商设备封装:16-SSOP 包装:带卷 (TR) 其它名称:NJW1504V-TE1-NDNJW1504V-TE1TR |
| LTC6946IUFD-1#TRPBF | 功能描述:IC INTEGER-N PLL W/VCO 28QFN RoHS:是 类别:集成电路 (IC) >> 时钟/计时 - 时钟发生器，PLL，频率合成器 系列:- 标准包装:1,000 系列:Precision Edge® 类型:时钟/频率合成器 PLL:无 输入:CML，PECL 输出:CML 电路数:1 比率 - 输入:输出:2:1 差分 - 输入:输出:是/是 频率 - 最大:10.7GHz 除法器/乘法器:无/无 电源电压:2.375 V ~ 3.6 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:16-VFQFN 裸露焊盘，16-MLF? 供应商设备封装:16-MLF?（3x3） 包装:带卷 (TR) 其它名称:SY58052UMGTRSY58052UMGTR-ND |
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