參數(shù)資料
型號(hào)： VCA822IDGS
廠商： Texas Instruments, Inc.
英文描述： Wideband, > 40dB Gain Adjust Range, Linear in V/V VARIABLE GAIN AMPLIFIER
中文描述： 寬帶，“40dB的增益調(diào)整范圍在V，線性音頻/視頻可變增益放大器
文件頁數(shù)： 25/35頁
文件大小： 837K
代理商： VCA822IDGS
www.ti.com
INPUT VOLTAGE DYNAMIC RANGE
V
= R
I
′
IN(PP)
RG(PP)
G
(9)
OUTPUT CURRENT AND VOLTAGE
R
=
GMIN
= 615.4
W
3.2V
PP
5.2mA
PP
(10)
OUTPUT VOLTAGE DYNAMIC RANGE
BANDWIDTH
VCA822
SBOS343A–SEPTEMBER 2007–REVISED OCTOBER 2007
As illustrated in
Equation 8
, once the output dynamic
range and maximum gain are defined, the gain
resistor is set. This gain setting in turn affects the
bandwidth, because in order to achieve the gain (and
with a set gain element), the feedback element of the
output stage amplifier is set as well. Keeping in mind
that the output amplifier of the
current-feedback amplifier, the larger the feedback
element, the lower the bandwidth as the feedback
resistor is the compensation element.
The VCA822 has a input dynamic range limited to
+1.6V
and –2.1V.
Increasing
dynamic range can be done by using an attenuator
network on the input. If the VCA822 is trying to
regulate the amplitude at the output, such as in an
AGC application, the input voltage dynamic range is
directly proportional to
Equation 9
.
the
input
voltage
VCA822
is
a
Limiting the discussion to the input voltage only and
ignoring the output voltage and gain,
Figure 3
illustrates the tradeoff between the input voltage and
the current flowing through the gain resistor.
As
conditions, the input voltage must be limited to the
CMIR of ±1.6V (3.2V
PP
) and the current (I
RQ
) must
flow through the gain resistor, ±2.6mA (5.2mA
PP
).
This configuration sets a minimum value for R
E
such
that the gain resistor has to be greater than
Equation 10
.
such,
for
unity-gain
or
under-attenuated
The VCA822 provides output voltage and current
capabilities that are unsurpassed in a low-cost
monolithic VCA. Under no-load conditions at +25
°
C,
the output voltage typically swings closer than 1V to
either supply rails; the +25
°
C swing limit is within
1.2V of either rails. Into a 15
load (the minimum
tested load), it is tested to deliver more than ±160mA.
Values lower than 615.4
are gain elements that
result in reduced input range, as the dynamic input
range is limited by the current flowing through the
gain resistor R
G
(I
RG
). If the I
RG
current is limiting the
performance of the circuit, the input stage of the
VCA822 goes into overdrive, resulting in limited
output voltage range. Such I
RG
-limited overdrive
conditions are shown in
Figure 53
for the gain of
+10V/V and
Figure 73
for the +100V/V gain.
The specifications described above, though familiar in
the industry, consider voltage and current limits
separately. In many applications, it is the voltage
×
current, or
V-I product
, that is more relevant to circuit
operation. Refer to the
Output Voltage and Current
Limitations
plot
(
Figure
Characteristics. The X- and Y-axes of this graph
show the zero-voltage output current limit and the
zero-current output voltage limit, respectively. The
four quadrants give a more detailed view of the
VCA822 output drive capabilities, noting that the
graph is bounded by a
Safe Operating Area
of 1W
maximum internal power dissipation. Superimposing
resistor load lines onto the plot shows that the
VCA822 can drive ±2.5V into 25
or ±3.5V into 50
without exceeding the output capabilities or the 1W
dissipation limit. A 100
load line (the standard test
circuit load) shows the full ±3.9V output swing
capability, as shown in the
Typical Characteristics
.
51
)
in
the
Typical
With its large output current capability and its wide
output voltage swing of ±3.9V typical on 100
load, it
is easy to forget other types of limitations that the
VCA822 can encounter. For these limitations, careful
analysis must be done to avoid input stage limitation,
either voltage or I
RG
current; also, consider the gain
limitation, as the control pin V
G
varies, affecting other
aspects of the circuit.
The output stage of the VCA822 is a wideband
current-feedback amplifier. As such, the feedback
resistance is the compensation of the last stage.
Reducing the feedback element and maintaining the
gain constant limits the useful range of I
RG
, and
therefore reducing the gain adjust range. For a given
gain, reducing the gain element limits the maximum
achievable output voltage swing.
The minimum specified output voltage and current
over-temperature are set by worst-case simulations at
the cold temperature extreme. Only at cold startup do
the output current and voltage decrease to the
numbers shown in the
Electrical Characteristic
tables.
As the output transistors deliver power, the respective
junction
temperatures
increase,
available output voltage swing, and increasing the
available output current. In steady-state operation,
the available output voltage and current is always
greater
than
that
temperature
over-temperature specifications because the output
stage junction temperatures are higher than the
specified operating ambient.
increasing
the
shown
in
the
Copyright 2007, Texas Instruments Incorporated
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VCA822
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VCA822IDGSR 功能描述:運(yùn)算放大器 - 運(yùn)放 WB >40dB Gain Adj Rng Lin V/V Var Gain RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補(bǔ)償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-16 轉(zhuǎn)換速度:0.89 V/us 關(guān)閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel
VCA822IDGSRG4 功能描述:運(yùn)算放大器 - 運(yùn)放 WB >40dB Gain Adj Rng Lin V/V Var Gain RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補(bǔ)償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-16 轉(zhuǎn)換速度:0.89 V/us 關(guān)閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel
VCA822IDGST 功能描述:運(yùn)算放大器 - 運(yùn)放 WB >40dB Gain Adj Rng Lin V/V Var Gain RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補(bǔ)償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-16 轉(zhuǎn)換速度:0.89 V/us 關(guān)閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel
VCA822IDGSTG4 功能描述:運(yùn)算放大器 - 運(yùn)放 WB >40dB Gain Adj Rng Lin V/V Var Gain RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補(bǔ)償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-16 轉(zhuǎn)換速度:0.89 V/us 關(guān)閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel
VCA822IDR 功能描述:運(yùn)算放大器 - 運(yùn)放 WB >40dB Gain Adj Rng Lin V/V Var Gain RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補(bǔ)償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-16 轉(zhuǎn)換速度:0.89 V/us 關(guān)閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel
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