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參數(shù)資料
| 型號： | LTC6945IUFD#PBF |
| 廠商： | Linear Technology |
| 文件頁數(shù)： | 11/28頁 |
| 文件大?。?/td> | 0K |
| 描述： | IC SYNTHESIZER INTEGER N 28QFN |
| 軟件下載： | PLLWizard™ PLLWizard™, with .NET 2.0 installer |
| 標(biāo)準(zhǔn)包裝： | 73 |
| 類型： | * |
| PLL： | 是 |
| 輸入： | 時鐘 |
| 輸出： | 時鐘 |
| 電路數(shù)： | 1 |
| 比率 - 輸入:輸出： | 1:1 |
| 差分 - 輸入:輸出： | 是/是 |
| 頻率 - 最大： | 6GHz |
| 除法器/乘法器： | 是/無 |
| 電源電壓： | 3.15 V ~ 5.25 V |
| 工作溫度： | -40°C ~ 105°C |
| 安裝類型： | 表面貼裝 |
| 封裝/外殼： | 28-WFQFN 裸露焊盤 |
| 供應(yīng)商設(shè)備封裝： | 28-QFN（4x5） |
| 包裝： | 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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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LTC6946-1 | 制造商:LINER 制造商全稱:Linear Technology 功能描述:30MHz to 1.4GHz IQ Demodulator |
| LTC6946-2 | 制造商:LINER 制造商全稱:Linear Technology 功能描述:30MHz to 1.4GHz IQ Demodulator |
| LTC6946-3 | 制造商:LINER 制造商全稱: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 類別:集成電路 (IC) >> 時鐘/計時 - 時鐘發(fā)生器，PLL，頻率合成器 系列:- 標(biāo)準(zhǔn)包裝:2,000 系列:- 類型:PLL 頻率合成器 PLL:是 輸入:晶體 輸出:時鐘 電路數(shù):1 比率 - 輸入:輸出:1:1 差分 - 輸入:輸出:無/無 頻率 - 最大:1GHz 除法器/乘法器:是/無 電源電壓:4.5 V ~ 5.5 V 工作溫度:-20°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:16-LSSOP（0.175"，4.40mm 寬） 供應(yīng)商設(shè)備封裝:16-SSOP 包裝:帶卷 (TR) 其它名稱:NJW1504V-TE1-NDNJW1504V-TE1TR |
| LTC6946IUFD-1#TRPBF | 功能描述:IC INTEGER-N PLL W/VCO 28QFN RoHS:是 類別:集成電路 (IC) >> 時鐘/計時 - 時鐘發(fā)生器，PLL，頻率合成器 系列:- 標(biāo)準(zhǔn)包裝:1,000 系列:Precision Edge® 類型:時鐘/頻率合成器 PLL:無 輸入:CML，PECL 輸出:CML 電路數(shù):1 比率 - 輸入:輸出:2:1 差分 - 輸入:輸出:是/是 頻率 - 最大:10.7GHz 除法器/乘法器:無/無 電源電壓:2.375 V ~ 3.6 V 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:16-VFQFN 裸露焊盤，16-MLF? 供應(yīng)商設(shè)備封裝:16-MLF?（3x3） 包裝:帶卷 (TR) 其它名稱:SY58052UMGTRSY58052UMGTR-ND |
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