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參數(shù)資料
| 型號： | VCA810IDR |
| 英文描述： | High Gain Adjust Range, Wideband, Voltage-Controlled Amplifier |
| 中文描述： | 高增益調(diào)整范圍，寬帶，電壓控制放大器 |
| 文件頁數(shù)： | 11/25頁 |
| 文件大小： | 417K |
| 代理商： | VCA810IDR |
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SBOS275C JUNE 2003 REVISED OCTOBER 2004
www.ti.com
11
APPLICATIONS INFORMATION
CIRCUIT DESCRIPTION
The VCA810 is a high gain adjust range, wideband,
voltage amplifier with a voltage-controlled gain, as shown
in Figure 1. The circuit’s basic voltage amplifier responds
to the control of an internal gain-control amplifier. At its
input, the voltage amplifier presents the high impedance of
a differential stage, permitting flexible input impedance
matching. To preserve termination options, no internal
circuitry connects to the input bases of this differential
stage. For this reason, the user must provide DC paths for
the input base currents from a signal source, either through
a grounded termination resistor or by a direct connection
to ground. The differential input stage also permits
rejection of common-mode signals. At its output, the
voltage amplifier presents a low impedance, simplifying
impedance matching. An open-loop design produces wide
bandwidth at all gain settings. A ground-referenced
differential to single-ended conversion at the output retains
the low output offset voltage.
+5V
5V
V
OUT
V
C
VCA810
X1
2
3
V+
V
1
8
Gain
Adjust
+
40dB
→
+40dB Gain
0
→
2V
Figure 1. Block Diagram of the VCA810
A gain control voltage, V
C
, controls the amplifier gain
magnitude through a high-speed control circuit. Gain
polarity can be either inverting or non-inverting, depending
upon the amplifier input driven by the input signal. The gain
control circuit presents the high-input impedance of a
non-inverting op amp connection. The control voltage pin
is referred to ground as shown in Figure 1. The control
voltage V
C
varies the amplifier gain according to the
exponential relationship
G
V V
10
2(VC
1)
.
This
G
(dB)
over the specified 40dB to +40dB range as V
C
varies from
translates
40
to
the
log
gain
relationship
V
C
1
dB. Thus, G
(dB)
varies linearly
0V to 2V. Optionally, making V
C
slightly positive (
≥
+0.15V) effectively disables the amplifier, giving > 80dB of
signal path attenuation at low frequencies.
Internally, the gain-control circuit varies the amplifier gain
by varying the transconductance, g
m
, of a bipolar
transistor using the transistor bias current. Varying the bias
currents of differential stages varies g
m
to control the
voltage gain of the VCA810. A g
m
-based gain adjust
normally suffers poor thermal stability. The VCA810
includes circuitry to minimize this effect.
VCA810 OPERATION
Figure 2 shows the circuit configuration used as the basis
of
the
Electrical
Characteristics
Characteristics.
Voltage
specifications are taken directly at the input and output
pins. For test purposes, the input impedance is set to 50
with a resistance to ground. A 25
resistance (R
T
) is
included on the V input to get bias current cancellation.
Proper supply bypassing is shown in Figure 2, and
consists of two capacitors on each supply pin: one large
electrolytic capacitor (2.2
μ
F to 6.8
μ
F), effective at lower
frequencies, and one small ceramic capacitor (0.1
μ
F) for
high frequency decoupling. For more information on
decoupling, refer to the
Board Layout
section.
and
Typical
in
swings
reported
the
VCA810
V
C
V
I
V
O
+5V
6
7
+
+
2
5
R
C
R
T
25
R
L
500
0.1
μ
F
6.8
μ
F
3
1
8
5V
0.1
μ
F
6.8
μ
F
R
S
50
50
Source
Figure 2. Variable Gain, Specification and Test
Circuit
Notice that both inverting and non-inverting inputs are
connected to ground with a resistor (R
S
and R
T
). Matching
the DC source impedance looking out of each input will
minimize input offset voltage error.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| VCA810IDRG4 | 功能描述:特殊用途放大器 High-Gain Adj Range Wideband Vltg-Cntrl RoHS:否 制造商:Texas Instruments 通道數(shù)量:Single 共模抑制比（最小值）: 輸入補(bǔ)償電壓: 工作電源電壓:3 V to 5.5 V 電源電流:5 mA 最大功率耗散: 最大工作溫度:+ 70 C 最小工作溫度:- 40 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-20 封裝:Reel |
| VCA811IDR | 制造商:Texas Instruments 功能描述:VCA811: HIGH GAIN ADJUST RANGE, WIDEBAND, VOLTAGE-CONTROLLE - Tape and Reel |
| VCA820 | 制造商:TI 制造商全稱:Texas Instruments 功能描述:Wideband, > 40dB Gain Adjust Range, Linear in V/V VARIABLE GAIN AMPLIFIER |
| VCA-8206 | 制造商:Quest Technology International Inc 功能描述: |
| VCA820ID | 功能描述:特殊用途放大器 150MHz BW w/ Linear RoHS:否 制造商:Texas Instruments 通道數(shù)量:Single 共模抑制比（最小值）: 輸入補(bǔ)償電壓: 工作電源電壓:3 V to 5.5 V 電源電流:5 mA 最大功率耗散: 最大工作溫度:+ 70 C 最小工作溫度:- 40 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-20 封裝:Reel |
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