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?cè)鲆娣糯笃?/td>
文件頁(yè)數(shù)： 22/35頁(yè)
文件大?。?/td> 837K
代理商： VCA822IDGS
www.ti.com
R
2
1.33k
W
+V
IN
R
G+
R
G
-
-
V
IN
R
9
1.27k
W
C
9
10 F
m
R
8
50
W
R
5
50
W
R
1
20
W
V
IN
R
10
75
W
VCA822
R
21
8.7k
W
C
5
1.42pF
R
17
17.5k
W
C
6
120nF
R
18
40k
W
C
7
100nF
V
OUT
V
G
DC
= +1V
75
Load
W
V
G
GND
V
REF
FB
V
OUT
VOLTAGE-CONTROLLED LOW-PASS FILTER
In the circuit of
Figure 86
, the VCA822 serves as the
variable-gain
element
of
low-pass filter. This section discusses how this
implementation expands the circuit voltage swing
capability over that normally achieved with the
equivalent
multiplier
implementation.
control voltage, V
G
, is calculated as according to the
simplified relationship in
Equation 4
:
G
2 R C
p
f =
(5)
V
OUT
V
IN
R
2
R
1
1
1 + s
R C
G
=
-
′
(4)
-
￡
0.8V
V
0.8V
G
￡
(6)
R
F
1k
W
+V
IN
R
G+
R
G
-
-
V
IN
FB
R
G
200
W
20
W
V
OUT
VCA822
Out
V
G
OPA690
24pF
C
V
IN
R
332
W
2
R
332
W
1
24pF
50
W
V + 1
2
R
F
R
G
G = 2
′
′
(7)
VCA822
SBOS343A–SEPTEMBER 2007–REVISED OCTOBER 2007
Figure 85. Differential Cable Equalizer
this circuit performs as if the amplifier were replaced
by a short circuit. Visually replacing the amplifier by a
short leaves a simple voltage-feedback amplifier with
a
feedback
resistor
bypassed
Replacing this gain with a variable gain, G, the pole
can be written as shown in
Equation 5
:
by
a
capacitor.
a
voltage-controlled
The
circuit
Because the VCA822 is most linear in the midrange,
the median of the adjustable pole should be set at V
G
= 0V (see
Figure 26
,
Figure 46
,
Figure 67
, and
Equation 6
). Selecting R
1
= R
2
= 332
, and targeting
a median frequency of 10MHz, the capacitance (C) is
24pF. Because the
OPA690
was selected for the
circuit of
Figure 86
, and in order to limit peaking in
the OPA690 frequency response, a capacitor equal to
C was added on the inverting mode to ground. This
architecture
has
the
high-frequency noise gain of the OPA690 to +2V/V,
ensuring
stability
and
response.
effect
of
setting
the
providing
flat
frequency
Once the median frequency is set, the maximum and
minimum frequencies can be determined by using V
G
= –0.8V and V
G
= +0.8V in the gain equation of
Equation 7
. Note that this is a first-order analysis and
does not take into consideration the open-loop gain
limitation of the OPA690.
Figure 86. Voltage-Control Low-Pass Filter
The response control results from amplification of the
feedback voltage applied to R
2
. First, consider the
case where the VCA822 produces G = 1V/V. Then
22
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Copyright 2007, Texas Instruments Incorporated
Product Folder Link(s):
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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