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參數(shù)資料
| 型號(hào)： | VCA2616 |
| 英文描述： | Dual, Variable-Gain Amplifier with Low-Noise Preamp |
| 中文描述： | 雙路，可變增益放大器的低噪聲前置放大器 |
| 文件頁數(shù)： | 9/19頁 |
| 文件大?。?/td> | 389K |
| 代理商： | VCA2616 |
VCA2616, VCA2611
SBOS234E
9
www.ti.com
VCA
—
OVERVIEW
The magnitude of the differential VCA input signal (from the
LNP or an external source) is reduced by a programmable
attenuation factor, set by the analog VCA Control Voltage
(VCA
CNTL
) at pin 43. The maximum attenuation factor is
further programmable by using the three MGS bits
(pins 40-42). Figure 3 illustrates this dual-adjustable charac-
teristic. Internally, the signal is attenuated by having the
analog VCA
CNTL
vary the channel resistance of a set of
shunt-connected FET transistors. The MGS bits effectively
adjust the overall size of the shunt FET by switching parallel
components in or out under logic control. At any given
maximum gain setting, the analog variable gain characteris-
tic is linear in dB as a function of the control voltage, and is
created as a piecewise approximation of an ideal dB-linear
transfer function. The VCA gain control circuitry is common
to both channels of the VCA2616 and VCA2611.
FIGURE 1. Simplified Block Diagram of the VCA2616.
FIGURE 2. Recommended Circuit for Coupling an External
Signal into the VCA Inputs.
FIGURE 3. Swept Attenuator Characteristic.
THEORY OF OPERATION
The VCA2616 and VCA2611 are dual-channel systems con-
sisting of three primary blocks: an LNP, a VCA, and a
Programmable Gain Amplifier (PGA). For greater system
flexibility, an onboard multiplexer is provided for the VCA
inputs, selecting either the LNP outputs or external signal
inputs. Figure 1 shows a simplified block diagram of the dual-
channel system.
LNP
—
OVERVIEW
The LNP input may be connected to provide active-feedback
signal termination, achieving lower system noise perfor-
mance than conventional passive shunt termination. Further
lower noise performance is obtained if signal termination is
not required. The unterminated LNP input impedance is
600k
. The LNP can process fully differential or single-
ended signals in each channel. Differential signal processing
results in significantly reduced 2nd-harmonic distortion and
improved rejection of common-mode and power-supply noise.
The first gain stage of the LNP is AC-coupled into its output
buffer with a 4.8
μ
s time constant (33kHz high-pass charac-
teristic). The buffered LNP outputs are designed to drive the
succeeding VCA directly or, if desired, external loads as low
as 135
with minimal impact on signal distortion. The LNP
employs very low impedance local feedback to achieve
stable gain with the lowest possible noise and distortion.
Four pin-programmable gain settings are available: 5dB,
17dB, 22dB, and 25dB. Additional intermediate gains can be
programmed by adding trim resistors between the Gain Strap
programming pins.
The common-mode DC level at the LNP output is nominally
2.5V, matching the input common-mode requirement of the
VCA for simple direct coupling. When external signals are
fed to the VCA, they should also be set up with a 2.5V
DC
common-mode level. Figure 2 shows a circuit that demon-
strates the recommended coupling method using an external
op amp. The V
CM
node shown in Figure 2 is the V
CM
output
(pin 19). Typical R and C values are shown, yielding a high-
pass time constant similar to that of the LNP. If a different
common-mode referencing method is used, it is important
that the common-mode level be within 10mV of the V
CM
output for proper operation.
V
CM
(+2.5V)
1k
1k
47nF
To VCA
IN
Input
Signal
VCA
LNP
Channel A
Input
VCA
Control
PGA
Channel A
Output
External
In
A
Maximum
Gain
Select
MGS
Analog
Control
VCA
LNP
Channel B
Input
PGA
Channel B
Output
External
In
B
0
–
24
V
–
45
Control Voltage (V)
0
Maximum Attenuation
Minimum Attenuation
3.0
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| VCA2616EVM | 功能描述:放大器 IC 開發(fā)工具 VCA2616 Eval Mod RoHS:否 制造商:International Rectifier 產(chǎn)品:Demonstration Boards 類型:Power Amplifiers 工具用于評(píng)估:IR4302 工作電源電壓:13 V to 23 V |
| VCA2616YR | 功能描述:特殊用途放大器 Dual Variable Gain 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 |
| VCA2616YT | 功能描述:特殊用途放大器 Dual Variable Gain 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 |
| VCA2617 | 制造商:BB 制造商全稱:BB 功能描述:Dual, Variable Gain Amplifier |
| VCA2617EVM | 功能描述:放大器 IC 開發(fā)工具 VCA2617 Eval Mod RoHS:否 制造商:International Rectifier 產(chǎn)品:Demonstration Boards 類型:Power Amplifiers 工具用于評(píng)估:IR4302 工作電源電壓:13 V to 23 V |
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