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參數(shù)資料
| 型號： | LMV794MA |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 運動控制電子 |
| 英文描述： | 88 MHz, Low Noise, 1.8V CMOS Input, Decompensated Operational Amplifiers |
| 中文描述： | DUAL OP-AMP, 1650 uV OFFSET-MAX, 88 MHz BAND WIDTH, PDSO8 |
| 封裝： | SOIC-8 |
| 文件頁數(shù)： | 18/22頁 |
| 文件大?。?/td> | 543K |
| 代理商： | LMV794MA |
Using feedback theory, F = V
/V
, this becomes a voltage
divider giving the following equation:
The noise gain is 1/F. Because this is a differentiator circuit,
a zero must be inserted. The location of the zero is given by:
C
has been added for stability. The addition of this part adds
a pole to the circuit. The pole is located at:
To attain maximum bandwidth and still have good stability the
pole is to be located on the open loop gain curve which is A.
If additional compensation is required one can always in-
crease the value of C
, but this will also reduce the bandwidth
of the circuit. Therefore A = 1/F, or AF = 1. For A the equation
is:
The expression f
GBW
is the gain bandwidth product of the part.
For a unity gain stable part this is the frequency where A = 1.
For the LMV793 f
= 88 MHz. Multiplying A and F results
in the following equation:
For the above equation s = j
ω
. To find the actual amplitude of
the equation the square root of the square of the real and
imaginary parts are calculated. At the intersection of F and A,
we have:
After a bit of algebraic manipulation the above equation re-
duces to:
In the above equation the only unknown is C
. In trying to
solve this equation the fourth power of C
must be dealt with.
An excel spread sheet with this equation can be used and all
the known values entered. Then through iteration, the value
of C
when both sides are equal will be found. That is the
correct value for C
F
, and of course the closest standard value
is used for C
F
.
Before moving the lab, the transfer function of the tran-
simpedance amplifier must be found and the units must be in
Ohms.
The LMV793 was evaluated for R
= 10 k
and 100 k
, rep-
resenting a somewhat lower gain configuration and with the
100 k
feedback resistor a fairly high gain configuration. The
R
= 10 k
is covered first. Looking at the
Input Common
Mode Capacitance vs. V
chart for C
for the operating
point selected C
= 15 pF. Note that for split supplies V
=
2.5V, C
= 22 pF and f
= 88 MHz. Solving for C
the cal-
culated value is 1.75 pF, so 1.8 pF is selected for use.
Checking the frequency of the pole finds that it is at 8.8 MHz,
which is right at the minimum gain recommended for this part.
Some over compensation was necessary for stability and the
final selected value for C
is 2.7 pF. This moves the pole to
5.9 MHz.
Figure 18
and
Figure 19
show the rise and fall times
obtained in the lab with a 1V output swing. The laser diode
was difficult to drive due to thermal effects making the starting
and ending point of the pulse quite different, therefore the two
separate scope pictures.
20216390
FIGURE 18. Fall Time
www.national.com
18
L
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LMV794MA/NOPB | 功能描述:運算放大器 - 運放 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 安裝風格:SMD/SMT 封裝 / 箱體:QFN-16 轉換速度:0.89 V/us 關閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
| LMV794MAX | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:88 MHz, Low Noise, 1.8V CMOS Input, Decompensated Operational Amplifiers |
| LMV794MAX/NOPB | 功能描述:運算放大器 - 運放 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 安裝風格:SMD/SMT 封裝 / 箱體:QFN-16 轉換速度:0.89 V/us 關閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
| LMV794MM | 制造商:Texas Instruments 功能描述:OP Amp Single GP R-R O/P 5.5V 8-Pin MSOP T/R |
| LMV794MM/NOPB | 功能描述:運算放大器 - 運放 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 安裝風格:SMD/SMT 封裝 / 箱體:QFN-16 轉換速度:0.89 V/us 關閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
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