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參數(shù)資料
| 型號(hào)： | LMF60CIN-100 |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 運(yùn)動(dòng)控制電子 |
| 英文描述： | LMF60 High Performance 6th-Order Switched Capacitor Butterworth Lowpass Filter |
| 中文描述： | SWITCHED CAPACITOR FILTER, BUTTERWORTH, LOWPASS, PDIP14 |
| 封裝： | 0.300 INCH, PLASTIC, DIP-14 |
| 文件頁數(shù)： | 13/20頁 |
| 文件大?。?/td> | 391K |
| 代理商： | LMF60CIN-100 |
1.0 LMF60 Application Hints
(Continued)
TL/H/9294–13
TL/H/9294–14
FIGURE 5. V
OS
Adjust Schemes
1.3 OFFSET ADJUST
The V
OS
ADJ pin is used in adjusting the output offset level
of the filter section. If this pin is not used it must be tied to
the analog ground (AGND) level, either mid-supply for single
ended supply operation or ground for split supply operation.
This pin sets the zero reference for the output of the filter.
The implementation of this pin can be seen in Figure 5. In
5(a) DC offset is adjusted using a potentiometer; in5(b) the
Op-Amp integrator circuit keeps the average DC output lev-
el at AGND. The circuit in 5(b) is therefore appropriate only
for AC-coupled signals and signals biased at AGND.
1.4 INPUT IMPEDANCE
The LMF60 lowpass filter input (FILTER IN pin) is not a high
impedance buffer input. This input is a switched capacitor
resistor equivalent, and its effective impedance is inversely
proportional to the clock frequency. The equivalent circuit of
the input to the filter can be seen in Figure 6. The input
capacitor charges to the input voltage (V
IN
) during one half
of the clock period, during the second half the charge is
transferred to the feedback capacitor. The total transfer of
charge in one clock cycle is therefore Q
e
C
IN
V
IN
, and
since current is defined as the flow of charge per unit time
the average input current becomes
I
IN
e
Q/T
(where T equals one clock period) or
I
IN
e
C
IN
V
IN
T
e
C
IN
V
IN
f
CLK
The equivalent input resistor (R
IN
) then can be defined as
R
IN
e
V
IN
/I
IN
e
1
C
IN
f
CLK
The input capacitor is 2 pF for the LMF60-50 and 1 pF for
the LMF60-100, so for the LMF60-100
R
IN
e
1
c
10
12
f
CLK
f
C
c
100
and
R
IN
e
5
c
10
11
f
CLK
f
C
c
50
for the LMF60-50. As shown in the above equations, for a
given cutoff frequency (f
C
) the input impedance remains the
same for the LMF60-50 and the LMF60-100. The higher the
clock to cutoff frequency ratio, the greater equivalent input
resistance for a given clock frequency. As the cutoff fre-
quency increases the equivalent input impedance decreas-
es. This input resistance will form a voltage divider with the
source impedance (R
SOURCE
). Since R
IN
is inversely pro-
portional to the cutoff frequency, operation at higher cutoff
frequencies will be more likely to load the input signal which
would appear as an overall decrease in gain at the output of
the filter. Since the filter’s ideal gain is unity, its overall gain
is given by:
e
1
c
10
12
e
1
c
10
10
f
C
e
5
c
10
11
e
1
c
10
10
f
C
A
V
e
R
IN
R
IN
a
R
SOURCE
TL/H/9294–15
a) Equivalent Circuit for LMF60 Filter Input
TL/H/9294–16
b) Actual Circuit for LMF60 Filter Input
FIGURE 6. LMF60 Filter Input
http://www.national.com
13
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| LMF60CIN-50 | LMF60 High Performance 6th-Order Switched Capacitor Butterworth Lowpass Filter |
| LMF60CIWM-50 | LMF60 High Performance 6th-Order Switched Capacitor Butterworth Lowpass Filter |
| LMF60CIWM-100 | LMF60 High Performance 6th-Order Switched Capacitor Butterworth Lowpass Filter |
| LMF60 | LMF60 High Performance 6th-Order Switched Capacitor Butterworth Lowpass Filter |
| LMFLSP100 | Super Luminosity White LED |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LMF60CIN-50 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:LMF60 High Performance 6th-Order Switched Capacitor Butterworth Lowpass Filter |
| LMF60CIWM-100 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:LMF60 High Performance 6th-Order Switched Capacitor Butterworth Lowpass Filter |
| LMF60CIWM-50 | 制造商:Texas Instruments 功能描述: |
| LMF60CMJ-100 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:LMF60 High Performance 6th-Order Switched Capacitor Butterworth Lowpass Filter |
| LMF60CMJ-100/883 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Analog Filter |
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