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| 型号： | THS4275MDEPR |
| 厂商： | TEXAS INSTRUMENTS INC |
| 元件分类： | 音频／视频放大 |
| 英文描述： | 1 CHANNEL, VIDEO AMPLIFIER, PDSO8 |
| 封装： | PLASTIC, SO-8 |
| 文件页数： | 19/36页 |
| 文件大小： | 598K |
| 代理商： | THS4275MDEPR |
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THS4271EP
THS4275EP
SGLS270A DECEMBER 2004 REVISED APRIL 2005
www.ti.com
26
3
2.5
2
1.5
1
0.5
0
0.5
1 M
10 M
100 M
f Frequency Hz
Normalized
Gain
dB
FREQUENCY RESPONSE
vs
CAPACITIVE LOAD
RL = 499
VS =±5 V
R(ISO) = 25 CL = 10 pF
R(ISO) = 15 CL = 100 pF
R(ISO) = 10 CL = 50 pF
Figure 89. Isolation Resistor Diagram
BOARD LAYOUT
Achieving optimum performance with a high frequency
amplifier like the THS4271 requires careful attention to
board layout parasitics and external component types.
Recommendations that optimize performance include:
1.
Minimize parasitic capacitance to any ac ground
for all of the signal I/O pins. Parasitic capacitance on
the output and inverting input pins can cause
instability: on the noninverting input, it can react with
the source impedance to cause unintentional band
limiting. To reduce unwanted capacitance, a window
around the signal I/O pins should be opened in all of
the ground and power planes around those pins.
Otherwise, ground and power planes should be
unbroken elsewhere on the board.
2.
Minimize the distance (< 0.25”) from the power
supply pins to high frequency 0.1-
mF decoupling
capacitors. At the device pins, the ground and power
plane layout should not be in close proximity to the
signal I/O pins. Avoid narrow power and ground traces
to minimize inductance between the pins and the
decoupling capacitors. The power supply connections
should always be decoupled with these capacitors.
Larger (2.2
F to 6.8 F) decoupling capacitors,
effective at lower frequency, should also be used on
the main supply pins. These may be placed somewhat
farther from the device and may be shared among
several devices in the same area of the PC board.
3.
Careful selection and placement of external
components
preserves
the
high
frequency
performance of the THS4271. Resistors should be
a low reactance type. Surface-mount resistors work
best and allow a tighter overall layout. Metal-film and
carbon composition, axially-leaded resistors can also
provide good high frequency performance. Again,
keep their leads and PC board trace length as short as
possible. Never use wire-wound type resistors in a
high frequency application. Since the output pin and
inverting input pin are the most sensitive to parasitic
capacitance, always position the feedback and series
output resistor, if any, as close as possible to the
output pin. Other network components, such as
noninverting input-termination resistors, should also
be placed close to the package. Where double-side
component mounting is allowed, place the feedback
resistor directly under the package on the other side
of the board between the output and inverting input
pins. Even with a low parasitic capacitance shunting
the external resistors, excessively high resistor values
can create significant time constants that can degrade
performance. Good axial metal-film or surface-mount
resistors have approximately 0.2 pF in shunt with the
resistor. For resistor values > 2 k
, this parasitic
capacitance can add a pole and/or a zero below
400 MHz that can effect circuit operation. Keep
resistor values as low as possible, consistent with
load driving considerations. A good starting point for
design is to set the Rf to 249 for low-gain,
noninverting applications. Doing this automatically
keeps the resistor noise terms low and minimizes the
effect of their parasitic capacitance.
4.
Connections to other wideband devices on the
board may be made with short direct traces or
through onboard transmission lines. For short
connections, consider the trace and the input to the
next device as a lumped capacitive load. Relatively
wide traces (50 mils to 100 mils) should be used,
preferably with ground and power planes opened up
around them. Estimate the total capacitive load and
set RISO from the plot of recommended RISO vs
capacitive load. Low parasitic capacitive loads
(<4 pF) may not need an R(ISO), since the THS4271
is nominally compensated to operate with a 2-pF
parasitic load. Higher parasitic capacitive loads
without an R(ISO) are allowed as the signal gain
increases (increasing the unloaded phase margin). If
a long trace is required, and the 6-dB signal loss
intrinsic to a doubly-terminated transmission line is
acceptable,
implement
a
matched
impedance
transmission
line
using
microstrip
or
stripline
techniques (consult an ECL design handbook for
microstrip and stripline layout techniques). A 50-
environment is normally not necessary onboard, and
in fact, a higher impedance environment improves
distortion as shown in the distortion versus load plots.
With a characteristic board trace impedance defined
based on board material and trace dimensions, a
matching series resistor into the trace from the output
of the THS4271 is used as well as a terminating shunt
resistor at the input of the destination device.
Remember also that the terminating impedance is the
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| THS4281DBVR | 功能描述:高速运算放大器 Very Lo-Pwr R-To-R I/O Voltage Feedback RoHS:否 制造商:Texas Instruments 通道数量:1 电压增益 dB:116 dB 输入补偿电压:0.5 mV 转换速度:55 V/us 工作电源电压:36 V 电源电流:7.5 mA 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:SOIC-8 封装:Tube |
| THS4281DBVRG4 | 功能描述:高速运算放大器 Very Lo-Pwr R-To-R I/O Voltage Feedback RoHS:否 制造商:Texas Instruments 通道数量:1 电压增益 dB:116 dB 输入补偿电压:0.5 mV 转换速度:55 V/us 工作电源电压:36 V 电源电流:7.5 mA 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:SOIC-8 封装:Tube |
| THS4281DBVT | 功能描述:高速运算放大器 Very Lo-Pwr R-To-R I/O Voltage Feedback RoHS:否 制造商:Texas Instruments 通道数量:1 电压增益 dB:116 dB 输入补偿电压:0.5 mV 转换速度:55 V/us 工作电源电压:36 V 电源电流:7.5 mA 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:SOIC-8 封装:Tube |
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