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| 型号： | THS3120CDG4 |
| 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： | GREEN, PLASTIC, MS-012AA, SOIC-8 |
| 文件页数： | 13/35页 |
| 文件大小： | 975K |
| 代理商： | THS3120CDG4 |
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SLOS420E – SEPTEMBER 2003 – REVISED OCTOBER 2009........................................................................................................................................ www.ti.com
PRINTED-CIRCUIT BOARD LAYOUT
Connections to other wideband devices on the
TECHNIQUES FOR OPTIMAL
board may be made with short direct traces or
PERFORMANCE
through onboard transmission lines. For short
connections, consider the trace and the input to
Achieving optimum performance with high frequency
the next device as a lumped capacitive load.
amplifiers, like the THS3120 and THS3121, requires
Relatively wide traces [0.05 inch (1,3 mm) to
careful attention to board layout parasitic and external
0.1 inch (2,54 mm)] should be used, preferably
component types. Recommendations that optimize
with ground and power planes opened up around
performance include:
them. Estimate the total capacitive load and
Minimize parasitic capacitance to any ac ground
determine if isolation resistors on the outputs are
for all of the signal I/O pins. Parasitic capacitance
necessary. Low parasitic capacitive loads (less
on the output and input pins can cause instability.
than 4 pF) may not need an RS because the
To reduce unwanted capacitance, a window
THS3120
and
THS3121
are
nominally
around the signal I/O pins should be opened in all
compensated to operate with a 2-pF parasitic
of the ground and power planes around those
load. Higher parasitic capacitive loads without an
pins. Otherwise, ground and power planes should
RS are allowed as the signal gain increases
be unbroken elsewhere on the board.
(increasing the unloaded phase margin). If a long
Minimize the distance [< 0.25 inch, (6,4 mm)] from
trace is required, and the 6-dB signal loss intrinsic
the power-supply pins to high frequency 0.1-
μF
to
a
doubly-terminated
transmission
line
is
and 100-pF decoupling capacitors. At the device
acceptable, implement a matched impedance
pins, the ground and power-plane layout should
transmission line using microstrip or stripline
not be in close proximity to the signal I/O pins.
techniques (consult an ECL design handbook for
Avoid
narrow
power
and
ground
traces
to
microstrip and stripline layout techniques). A 50-
minimize inductance between the pins and the
environment is not necessary onboard, and in
decoupling
capacitors.
The
power-supply
fact, a higher impedance environment improves
connections should always be decoupled with
distortion as shown in the distortion versus load
these
capacitors.
Larger
(6.8
μF
or
more)
plots. With a characteristic board trace impedance
tantalum decoupling capacitors, effective at lower
based on board material and trace dimensions, a
frequency, should also be used on the main
matching series resistor into the trace from the
supply pins. These may be placed somewhat
output of the THS3120/THS3121 is used as well
farther from the device and may be shared among
as a terminating shunt resistor at the input of the
several devices in the same area of the PC board.
destination
device.
Remember
also
that
the
terminating impedance is the parallel combination
Careful
selection
and
placement
of
external
of the shunt resistor and the input impedance of
components
preserve
the
high-frequency
the
destination
device:
this
total
effective
performance of the THS3120 and THS3121.
impedance should be set to match the trace
Resistors should be a very low reactance type.
impedance.
If
the
6-dB
attenuation
of
a
Surface-mount resistors work best and allow a
doubly-terminated
transmission
line
is
tighter overall layout. Again, keep the leads and
unacceptable,
a
long
trace
can
be
printed circuit board (PCB) trace length as short
series-terminated at the source end only. Treat
as possible. Never use wirewound type resistors
the trace as a capacitive load in this case. This
in a high-frequency application. Because the
does not preserve signal integrity as well as a
output pin and inverting input pins are the most
doubly-terminated line. If the input impedance of
sensitive to parasitic capacitance, always position
the destination device is low, there is some signal
the feedback and series output resistors, if any, as
attenuation due to the voltage divider formed by
close as possible to the inverting input pins and
the series output into the terminating impedance.
output pins. Other network components, such as
input termination resistors, should be placed close
Socketing a high-speed part like the THS3120 and
to the gain-setting resistors. Even with a low
THS3121 is not recommended. The additional
parasitic
capacitance
shunting
the
external
lead length and pin-to-pin capacitance introduced
resistors, excessively high resistor values can
by
the
socket
can
create
an
extremely
create significant time constants that can degrade
troublesome parasitic network which can make it
performance.
Good
axial
metal-film
or
almost impossible to achieve a smooth, stable
surface-mount
resistors
have
approximately
frequency response. Best results are obtained by
0.2 pF in shunt with the resistor. For resistor
soldering the THS3120/THS3121 parts directly
values
greater
than
2.0
k
,
this
parasitic
onto the board.
capacitance can add a pole and/or a zero that can
effect circuit operation. Keep resistor values as
low as possible, consistent with load driving
considerations.
20
Copyright 2003–2009, Texas Instruments Incorporated
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相关代理商/技术参数 |
参数描述 |
|---|---|
| THS3120CDGN | 功能描述:高速运算放大器 Single Lo-Noise Hi-Output 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 |
| THS3120CDGNG4 | 功能描述:高速运算放大器 Single Lo-Noise Hi-Output 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 |
| THS3120CDGNR | 功能描述:高速运算放大器 Single Lo-Noise Hi-Output 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 |
| THS3120CDGNRG4 | 功能描述:高速运算放大器 Single Lo-Noise Hi-Output 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 |
| THS3120CDR | 功能描述:高速运算放大器 Single Lo-Noise Hi-Output 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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