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| 型號： | THS4275MDEPR |
| 廠商： | TEXAS INSTRUMENTS INC |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 1 CHANNEL, VIDEO AMPLIFIER, PDSO8 |
| 封裝： | PLASTIC, SO-8 |
| 文件頁數(shù)： | 17/36頁 |
| 文件大小： | 598K |
| 代理商： | THS4275MDEPR |
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THS4271EP
THS4275EP
SGLS270A DECEMBER 2004 REVISED APRIL 2005
www.ti.com
24
directly. The total load includes the feedback network; in
the noninverting configuration (see Figure 76) this is the
sum of Rf and Rg, while in the inverting configuration (see
Figure 77), only Rf needs to be included in parallel with the
actual load.
LINEARITY: DEFINITIONS, TERMINOLOGY,
CIRCUIT TECHNIQUES, AND DESIGN
TRADEOFFS
The THS4271 features excellent distortion performance
for monolithic operational amplifiers. This section focuses
on the fundamentals of distortion, circuit techniques for
reducing nonlinearity, and methods for equating distortion
of operational amplifiers to desired linearity specifications
in RF receiver chains.
Amplifiers are generally thought of as linear devices. The
output of an amplifier is a linearly scaled version of the
input signal applied to it. However, amplifier transfer
functions are nonlinear. Minimizing amplifier nonlinearity
is a primary design goal in many applications.
Intercept points are specifications long used as key design
criteria in the RF communications world as a metric for the
intermodulation distortion performance of a device in the
signal chain (e.g., amplifiers, mixers, etc.). Use of the
intercept point, rather than strictly the intermodulation
distortion,
allows
simpler
system-level calculations.
Intercept points, like noise figures, can be easily cascaded
back and forth through a signal chain to determine the
overall
receiver
chain’s
intermodulation
distortion
performance. The relationship between intermodulation
distortion and intercept point is depicted in Figure 86 and
Figure 87.
Figure 86
IMD3 = PS PO
PS
PO
fc = fc f1
fc = f2 fc
PS
fc 3ff1 fc f2
fc + 3f
Power
f Frequency MHz
Figure 87
IMD3
OIP3
IIP3
3X
PIN
(dBm)
1X
POUT
(dBm)
PO
PS
Due to the intercept point’s ease of use in system level
calculations for receiver chains, it has become the
specification of choice for guiding distortion-related design
decisions. Traditionally, these systems use primarily
class-A, single-ended RF amplifiers as gain blocks. These
RF amplifiers are typically designed to operate in a 50-
environment. Giving intercept points in dBm, implies an
associated impedance (50
).
However, with an operational amplifier, the output does not
require termination as an RF amplifier would. Because
closed-loop amplifiers deliver signals to their outputs
regardless of the impedance present, it is important to
comprehend this when evaluating the intercept point of an
operational amplifier. The THS4271 yields optimum
distortion performance when loaded with 150
to 1 k,
which
is
similar
to
the
input
impedance
of
an
analog-to-digital converter over its input frequency band.
As a result, terminating the input of the ADC to 50
can
actually be detrimental to systems performance.
The discontinuity between open-loop, class-A amplifiers
and closed-loop, class-AB amplifiers becomes apparent
when comparing the intercept points of the two types of
devices. Equations 1 and 2 gives the definition of an
intercept point, relative to the intermodulation distortion.
OIP
3 + PO )
IMD
3
2
where
P
O + 10 log
V2
P
2R
L
0.001
NOTE: PO is the output power of a single tone, RL is the load
resistance, and VP is the peak voltage for a single tone.
(2)
(3)
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相關(guān)代理商/技術(shù)參數(shù) |
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| THS4281DBVR | 功能描述:高速運算放大器 Very Lo-Pwr R-To-R I/O Voltage Feedback RoHS:否 制造商:Texas Instruments 通道數(shù)量:1 電壓增益 dB:116 dB 輸入補償電壓:0.5 mV 轉(zhuǎn)換速度:55 V/us 工作電源電壓:36 V 電源電流:7.5 mA 最大工作溫度:+ 85 C 安裝風格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Tube |
| THS4281DBVRG4 | 功能描述:高速運算放大器 Very Lo-Pwr R-To-R I/O Voltage Feedback RoHS:否 制造商:Texas Instruments 通道數(shù)量:1 電壓增益 dB:116 dB 輸入補償電壓:0.5 mV 轉(zhuǎn)換速度:55 V/us 工作電源電壓:36 V 電源電流:7.5 mA 最大工作溫度:+ 85 C 安裝風格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Tube |
| THS4281DBVT | 功能描述:高速運算放大器 Very Lo-Pwr R-To-R I/O Voltage Feedback RoHS:否 制造商:Texas Instruments 通道數(shù)量:1 電壓增益 dB:116 dB 輸入補償電壓:0.5 mV 轉(zhuǎn)換速度:55 V/us 工作電源電壓:36 V 電源電流:7.5 mA 最大工作溫度:+ 85 C 安裝風格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Tube |
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