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| 型號： | THS4271DRBR |
| 廠商： | Texas Instruments, Inc. |
| 元件分類： | 運動控制電子 |
| 英文描述： | LOW NOISE, HIGH SLEW RATE, UNITY GAIN STABLE VOLTAGE FREEBACK AMPLIFIER |
| 中文描述： | 低噪聲，高擺率，單位增益穩(wěn)定電壓留言反饋放大器 |
| 文件頁數(shù)： | 19/38頁 |
| 文件大?。?/td> | 1055K |
| 代理商： | THS4271DRBR |
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SLOS397E JULY 2002 REVISED JANUARY 2004
www.ti.com
19
+
THS4271
Rg
249
RM
61.9
RT
130
100 pF
0.1
μ
F
6.8
μ
F
VS
5 V
50
Source
+
VI
100 pF
0.1
μ
F
6.8
μ
F
+
+VS
5 V
VO
CT
0.1
μ
F
Rf
249
499
Figure 76. Wideband, Inverting Gain
Configuration
In the inverting configuration, some key design
considerations must be noted. One is that the gain resistor
(R
g
) becomes part of the signal channel input impedance.
If the input impedance matching is desired (which is
beneficial whenever the signal is coupled through a cable,
twisted pair, long PC board trace, or other transmission
line conductors), R
g
may be set equal to the required
termination value and R
f
adjusted to give the desired gain.
However, care must be taken when dealing with low
inverting gains, as the resultant feedback resistor value
can present a significant load to the amplifier output. For
an inverting gain of 2, setting R
g
to 49.9
for input
matching eliminates the need for R
M
but requires a 100-
feedback resistor. This has an advantage of the noise gain
becoming equal to 2 for a 50-
source impedance—the
same as the noninverting circuit in Figure 75. However, the
amplifier output now sees the 100-
feedback resistor in
parallel with the external load. To eliminate this excessive
loading, it is preferable to increase both R
g
and R
f
, values,
as shown in Figure 76, and then achieve the input
matching impedance with a third resistor (R
M
) to ground.
The total input impedance becomes the parallel
combination of R
g
and R
M
.
The next major consideration is that the signal source
impedance becomes part of the noise gain equation and
hence influences the bandwidth. For example, the R
M
value combines in parallel with the external 50-
source
impedance (at high frequencies), yielding an effective
source impedance of 50
|| 61.9
= 27.7
. This
impedance is then added in series with R
g
for calculating
the noise gain. The result is 1.9 for Figure 76, as opposed
to the 1.8 if R
M
is eliminated. The bandwidth is lower for the
gain of –2 circuit, Figure 76, (NG=+1.9) than for the gain
of +2 circuit in Figure 75.
The last major consideration in inverting amplifier design
is setting the bias current cancellation resistor on the
noninverting input. If the resistance is set equal to the total
dc resistance looking out of the inverting terminal, the
output dc error, due to the input bias currents, is reduced
to (input offset current) multiplied by R
f
in Figure 76, the dc
source impedance looking out of the inverting terminal is
249
|| (249
+ 27.7
)
= 130
.
To reduce the additional
high-frequency noise introduced by the resistor at the
noninverting input, and power-supply feedback, R
T
is
bypassed with a capacitor to ground.
SINGLE SUPPLY OPERATION
The THS4271 is designed to operate from a single 5-V to
15-V power supply. When operating from a single power
supply, care must be taken to ensure the input signal and
amplifier are biased appropriately to allow for the
maximum output voltage swing. The circuits shown in
Figure 77 demonstrate methods to configure an amplifier
in a manner conducive for single supply operation.
_
+
THS4271
49.9
50
Source
VI
+VS
VO
Rf
249
Rg
249
+VS
2
+VS
2
_
+
THS4271
249
RT
50
Source
VI
VS
VO
Rf
249
+VS
2
+VS
2
61.9
Rg
499
RT
499
Figure 77. DC-Coupled Single Supply Operation
Saving Power With Power-Down Functionality
and Setting Threshold Levels With the Reference
Pin
The THS4275 features a power-down pin (PD) which
lowers the quiescent current from 22 mA down to 700
μ
A,
ideal for reducing system power.
The power-down pin of the amplifiers defaults to the
positive supply voltage in the absence of an applied
voltage, putting the amplifier in the power-on mode of
operation. To turn off the amplifier in an effort to conserve
power, the power-down pin can be driven towards the
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| THS4275DRBR | LOW NOISE, HIGH SLEW RATE, UNITY GAIN STABLE VOLTAGE FREEBACK AMPLIFIER |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| THS4271DRBRG4 | 功能描述:高速運算放大器 Super-Fast Ultra-Low Distortion 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(fēng)格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Tube |
| THS4271DRBT | 功能描述:高速運算放大器 Super-Fast Ultra-Low Distortion 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(fēng)格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Tube |
| THS4271DRBTG4 | 功能描述:高速運算放大器 Super-Fast Ultra-Low Distortion 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(fēng)格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Tube |
| THS4271DRG4 | 功能描述:高速運算放大器 Super-Fast Ultra-Low Distortion 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(fēng)格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Tube |
| THS4271-EP | 制造商:TI 制造商全稱:Texas Instruments 功能描述:LOW NOISE, HIGH SLEW RATE, UNITY GAIN STABLE VOLTAGE FEEDBACK AMPLIFIER |
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