- 您现在的位置：买卖IC网 > PDF目录371012 > MC144144P (MOTOROLA INC) Digital Signal Processors 44-JLCC -55 to 125 PDF资料下载
参数资料
| 型号： | MC144144P |
| 厂商： | MOTOROLA INC |
| 元件分类： | 颜色信号转换 |
| 英文描述： | Digital Signal Processors 44-JLCC -55 to 125 |
| 中文描述： | COLOR SIGNAL DECODER, PDIP18 |
| 封装： | PLASTIC, DIP-18 |
| 文件页数： | 38/44页 |
| 文件大小： | 565K |
| 代理商： | MC144144P |
第1页第2页第3页第4页第5页第6页第7页第8页第9页第10页第11页第12页第13页第14页第15页第16页第17页第18页第19页第20页第21页第22页第23页第24页第25页第26页第27页第28页第29页第30页第31页第32页第33页第34页第35页第36页第37页当前第38页第39页第40页第41页第42页第43页第44页
MC144144
38
MOTOROLA
tor type circuits, and cause digital signals to be misinter-
preted as wrong values.
When laying out the PCB, use electrolytic capacitors of
sufficient size at the power input to the printed circuit board.
Adding low ESR (effective series resistance) decoupling ca-
pacitors of about 0.1 mF capacitance between VDD(A) and
ground and VDD(D) and ground at the device power pins will
help reduce noise in general, and also reduce EMI and ESD
(electrostatic discharge) susceptibility. Implementation of a
good ground plane ground system can all but eliminate the
type of noise described above.
To summarize, use sufficient electrolytic capacitor filtering,
make separate ground planes for analog ground and digital
ground, tie these grounds together at one and only one point,
keep the ground planes as continuous and unbroken as pos-
sible, use low ESR capacitors of about 0.1 mF capacitance
on VDD(A) and VDD(D) at each device, and keep all leads as
short as possible.
EMI SUPRESSION
When using ICs in or near television receiver circuits, EMI
(electromagnetic interference) and subsequent unwanted
display artifacts and distortion are probable unless adequate
EMI suppression is implemented. A common misconception
is that some offending digital device is the culprit. This is er-
roneous in that an IC itself has insufficient surface area to
produce sufficient radiation. The device, while it is the gener-
ator of interfering signals, must be coupled to an antenna be-
fore EMI is radiated. The source for the EMI is not the IC
which generates the offending signals but rather the circuitry
which is attached to the IC.
Potential EMI signals are generated by
all
digital devices.
Whether they become a nuisance is dependent upon their
frequency and whether they have a sufficient antenna. The
frequency and number of these signals is affected by both
circuit design within the IC and the manufacturing process.
Device speed is also a major contributor of potential EMI. Be-
cause the design is determined by the anticipated applica-
tion, the manufacturing process is fixed and the drive for
speed ever increasing, the only effective point to implement
EMI suppression is in the PC board design. The PC board
usually is the antenna which radiates the EMI. The most effi-
cient method of minimizing EMI radiation is to minimize the
efficiency of this antenna.
The most common cause of inadequate EMI suppression
lies with the ground system of the suspected digital devices.
As pointed out previously, di/dt transitions can be significant
in digital circuits. If the di/dt transitions appear in the ground
system and the ground system is inductive, the harmonics
present in these transitions are a source of potential EMI sig-
nals. The unfortunate result of putting digital devices on a
reactive ground system is guaranteed EMI problems.
The area which should be addressed first as a potential
EMI source is the ground. Without an adequate ground sys-
tem, EMI cannot be effectively reduced by decoupling. If at
all possible, the ground should be a complete unbroken
plane. Figure 10 shows two examples of relieving ground
around device pins. When relieving vias and plated through
holes, large areas of ground loss should be avoided. When
the relief pattern is equal to half the distance between pins,
over–etching and process errors may remove ground
between pins. If sufficient ground around enough pins is re-
moved, the ground system can become isolated or nearly
isolated “patches” which will appear inductive. If ground,
such as the vicinity of an IC, must be removed, replace with
a cross hatch of ground lines with the mesh as small as pos-
sible.
If a single unbroken plane can be devoted to the ground
system, EMI can usually be sufficiently suppressed by using
ferrite beads on suspect EMI paths and decoupling with ade-
quate values of capacitors. The value of the decoupling ca-
pacitor depends on the frequency and amplitude of the
offending signals. Ferrite beads are available in a wide vari-
ety of shape, size, and material to fit virtually any application.
Choose a ferrite bead for desired impedance at the de-
sired frequency and construct a low pass filter using one or
more appropriate capacitors in a “L”, “T”, or “PI” arrange-
ment. Use only capacitors of low inductive and resistive
properties such as ceramic or mica. Install filters in series
with each IC pin suspected of contributing offending EMI sig-
nals and as close to the pin as possible. Analysis using a
spectrum analyzer can help determine which pins are sus-
pect.
Where PC board costs constrain the number of layers
available, and if the EMI frequencies are far removed from
the frequencies of operation, ferrite beads and decoupling
capacitors may still be effective in reducing EMI emissions.
Where only two (or in some cases, only one!) layer is used,
the ground system is always reactive and poses an EMI
problem. If the offending EMI and normal operating frequen-
cy differ sufficiently, filtering can still work.
An “island” is constructed in the ground system for the digi-
tal device using ferrite beads and decoupling capacitors as
shown by the example in Figure 11. The ground must be cut
so that the digital ground for the device is isolated from the
rest of the ground system. Next choose a ferrite bead of the
appropriate value. Install this bead between the isolated
ground and the ground system. Install low pass filters in all
suspect lines with the capacitor closest to the device pin con-
nected to the isolated ground in all signal lines where EMI is
suspect. Also cut the power to the device and insert a ferrite
bead as shown in Figure 11. Finally, decouple the device be-
tween the power pin(s) and isolated ground pin(s) using a
low inductive/resistive capacitor of adequate value.
The methods described above will work acceptably when
the EMI frequency and the frequency of operation of the de-
vice generating the EMI differ greatly. Where the EMI is dis-
turbing the high VHF or UHF channels and the device
generating the EMI is operating within the NTSC/PAL band-
width, the energy contained in the harmonics generating the
EMI is situated well above the operating frequency and
suppressing this type of EMI poses no great problem. How-
ever, if the EMI is present on low VHF channels and/or the
operation of the device is outside the NTSC/PAL bandwidth,
such as a 2X pixel clock or 4fsc oscillator, compromise be-
tween video quality and suppression complexity is usually
required to obtain an acceptable solution. For those cases
where the operating frequency of the device is very near the
frequency of the EMI disturbance, careful attention to PCB
layout, multiple layer PCB, and even shielding may be nec-
essary to obtain an acceptable design.
相关PDF资料 |
PDF描述 |
|---|---|
| MC14415DW | Digital Signal Processors 40-CDIP SB -55 to 125 |
| MC14415FL | Quad Precision Timer/Driver |
| MC14415FP | Quad Precision Timer/Driver |
| MC14415VL | Digital Signal Processors 68-CPGA -55 to 125 |
| MC14415VP | Digital Signal Processors 68-LCCC -55 to 125 |
相关代理商/技术参数 |
参数描述 |
|---|---|
| MC14415FP | 制造商:Motorola Inc 功能描述: |
| MC14416P | 制造商:Motorola Inc 功能描述: 制造商:Motorola Inc 功能描述:TIME-SLOT ASSIGNER, 22 Pin, Plastic, DIP |
| MC14419P | 制造商:Motorola Inc 功能描述:ENCODER, 16 Pin, Plastic, DIP |
| MC14433P | 制造商:Motorola Inc 功能描述: |
| MC1443G | 制造商:Motorola Inc 功能描述: |
发布紧急采购，3分钟左右您将得到回复。