參數(shù)資料
型號(hào)： MC145156
廠商： Motorola, Inc.
英文描述： Parallel-Input PLL Frequency Synthesizer
中文描述： 并行輸入鎖相環(huán)頻率合成器
文件頁(yè)數(shù)： 29/36頁(yè)
文件大?。?/td> 718K
代理商： MC145156
MC145151–2 through MC145158–2
MOTOROLA
29
CRYSTAL OSCILLATOR CONSIDERATIONS
The following options may be considered to provide a ref-
erence frequency to Motorola’s CMOS frequency synthe-
sizers.
Use of a Hybrid Crystal Oscillator
Commercially available temperature–compensated crystal
oscillators (TCXOs) or crystal–controlled data clock oscilla-
tors provide very stable reference frequencies. An oscillator
capable of sinking and sourcing 50
μ
A at CMOS logic levels
may be direct or dc coupled to OSCin. In general, the highest
frequency capability is obtained utilizing a direct–coupled
square wave having a rail–to–rail (VDD to VSS) voltage
swing. If the oscillator does not have CMOS logic levels on
the outputs, capacitive or ac coupling to OSCin may be used.
OSCout, an unbuffered output, should be left floating.
For additional information about TCXOs and data clock
oscillators, please consult the latest version of the
eem Elec-
tronic Engineers Master Catalog,
the
Gold Book,
or similar
publications.
Design an Off–Chip Reference
The user may design an off–chip crystal oscillator using
ICs specifically developed for crystal oscillator applications,
such as the MC12061 MECL device. The reference signal
from the MECL device is ac coupled to OSCin. For large am-
plitude signals (standard CMOS logic levels), dc coupling is
used. OSCout, an unbuffered output, should be left floating.
In general, the highest frequency capability is obtained with a
direct–coupled square wave having rail–to–rail voltage
swing.
Use of the On–Chip Oscillator Circuitry
The on–chip amplifier (a digital inverter) along with an ap-
propriate crystal may be used to provide a reference source
frequency. A fundamental mode crystal, parallel resonant at
the desired operating frequency, should be connected as
shown in Figure 10.
Figure 10. Pierce Crystal Oscillator Circuit
R1*
C2
C1
FREQUENCY
SYNTHESIZER
OSCout
OSCin
* May be deleted in certain cases. See text.
Rf
For VDD = 5.0 V, the crystal should be specified for a load-
ing capacitance, CL, which does not exceed 32 pF for fre-
quencies to approximately 8.0 MHz, 20 pF for frequencies in
the area of 8.0 to 15 MHz, and 10 pF for higher frequencies.
These are guidelines that provide a reasonable compromise
between IC capacitance, drive capability, swamping varia-
tions in stray and IC input/output capacitance, and realistic
CL values. The shunt load capacitance, CL, presented
across the crystal can be estimated to be:
CinCout
Cin + Cout
where
Cin= 5 pF (see Figure 11)
Cout= 6 pF (see Figure 11)
Ca= 1 pF (see Figure 11)
CO= the crystal’s holder capacitance
(see Figure 12)
C1 and C2 = external capacitors (see Figure 10)
CL =
+ Ca + Co +C1 + C2
C2
Figure 11. Parasitic Capacitances of the Amplifier
Cin
Cout
Ca
Figure 12. Equivalent Crystal Networks
NOTE: Values are supplied by crystal manufacturer
(parallel resonant crystal).
2
1
2
1
2
1
RS
LS
CS
Re
Xe
CO
The oscillator can be “trimmed” on–frequency by making a
portion or all of C1 variable. The crystal and associated com-
ponents must be located as close as possible to the OSCin
and OSCout pins to minimize distortion, stray capacitance,
stray inductance, and startup stabilization time. In some
cases, stray capacitance should be added to the value for Cin
and Cout.
Power is dissipated in the effective series resistance of the
crystal, Re, in Figure 12. The drive level specified by the crys-
tal manufacturer is the maximum stress that a crystal can
withstand without damage or excessive shift in frequency. R1
in Figure 10 limits the drive level. The use of R1 may not be
necessary in some cases (i.e., R1 = 0
).
To verify that the maximum dc supply voltage does not
overdrive the crystal, monitor the output frequency as a func-
tion of voltage at OSCout. (Care should be taken to minimize
loading.) The frequency should increase very slightly as the
dc supply voltage is increased. An overdriven crystal will de-
crease in frequency or become unstable with an increase in
supply voltage. The operating supply voltage must be re-
duced or R1 must be increased in value if the overdriven
condition exists. The user should note that the oscillator
start–up time is proportional to the value of R1.
Through the process of supplying crystals for use with
CMOS inverters, many crystal manufacturers have devel-
oped expertise in CMOS oscillator design with crystals. Dis-
cussions with such manufacturers can prove very helpful
(see Table 1).
相關(guān)PDF資料
PDF描述
MC145155DW2 Parallel-Input PLL Frequency Synthesizer
MC145156P2 Parallel-Input PLL Frequency Synthesizer
MC145151FN2 Parallel-Input PLL Frequency Synthesizer
MC145152DW2 Parallel-Input PLL Frequency Synthesizer
MC145155P2 CONNECTOR ACCESSORY
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
MC145158-2 制造商:Motorola Inc 功能描述:
MC145158DW2 功能描述:IC SER-IN PLL FREQ SYNTH 16-SOIC RoHS:否 類(lèi)別:集成電路 (IC) >> 時(shí)鐘/計(jì)時(shí) - 時(shí)鐘發(fā)生器，PLL，頻率合成器 系列:- 標(biāo)準(zhǔn)包裝:39 系列:- 類(lèi)型:* PLL:帶旁路 輸入:時(shí)鐘 輸出:時(shí)鐘 電路數(shù):1 比率 - 輸入:輸出:1:10 差分 - 輸入:輸出:是/是 頻率 - 最大:170MHz 除法器/乘法器:無(wú)/無(wú) 電源電壓:2.375 V ~ 3.465 V 工作溫度:0°C ~ 70°C 安裝類(lèi)型:* 封裝/外殼:* 供應(yīng)商設(shè)備封裝:* 包裝:*
MC145158DW2R2 制造商: 功能描述: 制造商:undefined 功能描述:
MC145159FN1R2 制造商:Motorola Inc 功能描述:
MC145159P1 制造商:Motorola Inc 功能描述:
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