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參數(shù)資料
| 型號(hào)： | LMH6502MAX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 模擬信號(hào)調(diào)理 |
| 英文描述： | Wideband, Low Power, Linear-in-dB Variable Gain Amplifier |
| 中文描述： | SPECIALTY ANALOG CIRCUIT, PDSO14 |
| 封裝： | SOIC-14 |
| 文件頁數(shù)： | 14/19頁 |
| 文件大?。?/td> | 941K |
| 代理商： | LMH6502MAX |
Typical Performance Characteristics
Unless otherwise specified: V
S
=
±
5V, 25C, V
G
= V
GMAX
, V
CM
= 0V, R
= 1k
, R
G
= 174
, both inputs terminated in 50
, R
L
= 100
, Typical values, results referred to device
output. (Continued)
Feedthrough from V
G
20067765
Application Information
THEORY OF OPERATION
A simplified schematic is shown in
Figure 1
. +V
IN
and V
IN
are buffered with closed loop voltage followers inducing a
signal current in Rg proportional to (+V
IN
) - (V
IN
), the dif-
ferential input voltage. This current controls a current source
which supplies two well-matched transistor, Q1 and Q2.
The current flowing through Q2 is converted to the final
output voltage using R
F
and the output amplifier, U1. By
changing the fraction of the signal current "I" which flows
through Q2, the gain is changed. This is done by changing
the voltage applied differentially to the bases of Q1 and Q2.
For example, with V
= 0V, Q1 conducts heavily and Q2 is
off. With none of "I" flowing through R
, the LMH6502’s input
to output gain is strongly attenuated. With V
= +2V, Q1 is off
and the entire signal current flows through Q2 to R
produc-
ing maximum gain. With V
set to 1V, the bases of Q1 and
Q2 are set to approximately the same voltage, Q1 and Q2
have the same collector currents - equal to one half of the
signal current "I", thus the gain is approximately one half the
maximum gain.
CHOOSING R
F
& R
G
Maximum input amplitude and maximum gain are the two
key specifications that determine component values in a
LMH6502 application.
The output stage op amp is a current-feedback type amplifier
optimized for R
F
= 1k
. R
G
can then be computed as:
(1)
To determine whether the maximum input amplitude will
overdrive the LMH6502, compute:
V
DMAX
= (R
G
+ 3.0
) x 1.70mA
the maximum differential input voltage for linear operation. If
the maximum input amplitude exceeds the above V
DMAX
limit, then LMH6502 should either be moved to a location in
the signal chain where input amplitudes are reduced, or the
LMH6502 gain A
VMAX
should be reduced or the values for
R
and R
should be increased. The overall system perfor-
mance impact is different based on the choice made. If the
input amplitude is reduced, re-compute the impact on signal-
to-noise ratio. If A
is reduced, post LMH6502 amplifier
gain, should be increased, or another gain stage added to
make up for reduced system gain. To increase R
G
and R
F
,
compute the lowest acceptable value for R
G
:
R
G
>
590 x V
DMAX
- 3
Operating with R
larger than this value insures linear op-
eration of the input buffers.
R
may be computed from selected R
and A
: R
F
should be
>
= 1k
for overall best performance, however R
F
<
1k
can be implemented if necessary using a loop gain
reducing resistor to ground on the inverting summing node of
the output amplifier (see application note QA-13 for details).
(2)
(3)
ADJUSTING OFFSET
Offset can be broken into two parts; an input-referred term
and an output-referred term. The input-referred offset shows
up as a variation in output voltage as V
G
is changed. This
can be trimmed using the circuit in
Figure 2
by placing a low
frequency square wave (V
LOW
= 0V, V
HIGH
= 2V into V
G
with
20067741
FIGURE 1. LMH6502 Block Diagram
L
www.national.com
14
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LMH6502MAX/NOPB | 功能描述:特殊用途放大器 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 |
| LMH6502MT | 功能描述:特殊用途放大器 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 |
| LMH6502MT/NOPB | 功能描述:特殊用途放大器 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 |
| LMH6502MTX | 功能描述:特殊用途放大器 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 |
| LMH6502MTX/NOPB | 功能描述:特殊用途放大器 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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