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參數(shù)資料
| 型號(hào)： | LMH6504MMX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 模擬信號(hào)調(diào)理 |
| 英文描述： | Wideband, Low Power, Variable Gain Amplifier |
| 中文描述： | SPECIALTY ANALOG CIRCUIT, PDSO8 |
| 封裝： | MSOP-8 |
| 文件頁數(shù)： | 12/19頁 |
| 文件大?。?/td> | 759K |
| 代理商： | LMH6504MMX |
Application Information
GENERAL DESCRIPTION
The key features of the LMH6504 are:
Low power
Broad voltage controlled gain and attenuation range
(From A
VMAX
down to complete cutoff)
Bandwidth independent, resistor programmable gain
range (R
G
)
Broad signal and gain control bandwidths
Frequency response may be adjusted with R
F
High impedance signal and gain control inputs
Refer to
Figure 1
below. The LMH6504 combines a closed
loop input buffer (“X1” Block), a voltage controlled variable
gain cell (“MULT” Block) and an output amplifier (“CFA”
Block). The input buffer is a transconductance stage whose
gain is set by the gain setting resistor, R
. The output
amplifier is a current feedback op amp and is configured as
a transimpedance stage whose gain is set by, and is equal
to, the feedback resistor, R
. The maximum gain, A
, of
the LMH6504 is defined by the ratio: K · R
/ R
where “K” is
the gain multiplier with a nominal value of 0.965. As the gain
control input (V
) changes over its 0 to 2V range, the gain is
adjusted over a range of about 80 dB relative to the maxi-
mum set gain.
SETTING THE LMH6504 MAXIMUM GAIN
Eq. 1
Although the LMH6504 is specified at A
= 9.7V/V, the
recommended A
varies between 2 and 100. Higher
gains are possible but usually impractical due to output
offsets, noise and distortion. When varying A
VMAX
several
tradeoffs are made:
R
G
: determines the input voltage range
R
F
: determines overall bandwidth
The amount of current which the input buffer can source/sink
into R
is limited and is specified in the I
RG_MAX
spec. This
sets the maximum input voltage:
Eq. 2
As the I
limit is approached (with increasing input
voltage or with lowering of R
G
), the device harmonic distor-
tion will increase. Changes in R
F
will have a dramatic effect
on the small signal bandwidth. The output amplifier of the
LMH6504 is a current feedback amplifier (CFA) and its band-
width is determined by R
F
. As with any CFA, doubling the
feedback resistor will roughly cut the bandwidth of the device
in half. For more about CFA’s, see the basic tutorial, OA-20,
“Current Feedback Myths Debunked”, or a more rigorous
analysis, OA-13, “Current Feedback Amplifier Loop Gain
Analysis and Performance Enhancements”.
OTHER CONFIGURATIONS
1) Single Supply Operation
The LMH6504 can be configured for use in a single supply
environment. Doing so requires the following:
a) Bias pin 4 and R
G
to a “virtual half supply” somewhere
close to the middle of V
+
and V
-
range. The other end of
R
is tied to pin 3. The “virtual half supply” needs to be
capable of sinking and sourcing the expected current flow
through R
G
.
b) Ensure that V
can be adjusted from 0V to 2V above the
“virtual half supply”.
c) Bias the input (pin 2) to make sure that it stays within the
range of 1.8V above V
-
to 1.8V below V
+
(see “Input
voltage Range” specification in the Electrical Character-
istics table). This can be accomplished by either DC
biasing the input and AC coupling the input signal, or
alternatively, by direct coupling if the output of the driving
stage is also biased to half supply.
Arranged this way, the LMH6504 will respond to the current
flowing through R
G
. The gain control relationship will be
similar to the split supply arrangement with V
G
measured
referenced to pin 4. Keep in mind that the circuit described
above will also center the output voltage to the “virtual half
supply voltage”.
2) Arbitrarily Referenced Input Signal
Having a wide input voltage range on the input (pin 2)
(+/-3.2V typical), the LMH6504 can be configured to control
the gain on signals which are not referenced to ground (e.g.
Half Supply biased circuits, etc.). We will call this node the
“reference node”. In such cases, the other end of R
(the
side not tied to pin 3) can be tied to this reference node so
that R
will “l(fā)ook at” the difference between the signal and
this reference only. Keep in mind that the reference node
needs to source and sink the current flowing through R
G
.
GAIN ACCURACY
Gain accuracy is defined as the actual gain compared
against the theoretical gain at a certain V
G
(results ex-
pressed in dB) (See
Figure 2
).
Theoretical gain is given by:
20084347
FIGURE 1. LMH6504 Typical Application and Block
Diagram
L
www.national.com
12
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LMH6504MMX/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 |
| LMH6505 | 制造商:INTERSIL 制造商全稱:Intersil Corporation 功能描述:Wideband, Low Power, Linear-in-dB, Variable Gain Amplifier |
| LMH6505MA | 制造商:Texas Instruments 功能描述:IC VGA WIDEBAND POWERWISE SOIC8 制造商:Texas Instruments 功能描述:IC, VGA WIDEBAND, POWERWISE, SOIC8 制造商:Texas Instruments 功能描述:IC, VARIABLE GAIN AMP, 150MHZ, SOIC-8 |
| LMH6505MA/NOPB | 功能描述:特殊用途放大器 Variable Gain Amp 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 |
| LMH6505MAX | 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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