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參數資料
| 型號： | LMF90CCN |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 模擬濾波器 |
| 英文描述： | 4th-Order Elliptic Notch Filter |
| 中文描述： | SWITCHED CAPACITOR FILTER, ELLIPTIC, NOTCH, PDIP14 |
| 封裝： | 0.300 INCH, PLASTIC, DIP-14 |
| 文件頁數： | 10/22頁 |
| 文件大小： | 411K |
| 代理商： | LMF90CCN |
Pin Descriptions
W (Pin 1)
This three-level logic input sets the width of
the notch. Notch width is f
c2
–f
c1
(seeFigure
1 ). When W is tied to V
(pin 14), GND (pin
13), or V
(pin 8), the notch width is 0.55 f
0
,
0.26 f
0
, or 0.127 f
0
, respectively.
This three-level logic input sets the ratio of
the clock frequency (f
CLK
) to the center fre-
quency (f
0
). When R is tied to V
, GND, or
V
, the clock-to-center-frequency ratio is
33.33:1, 50:1, or 100:1, respectively.
R (Pin 2)
LD (Pin 3)
This three-level logic input sets the division
factor of the clock frequency divider. When
LD is tied to V
, GND, or V
, the division
factor is 716, 596, or 2, respectively.
XTAL2 (Pin 4) This is the output of the internal crystal os-
cillator. When using the internal oscillator,
the crystal should be tied between XTAL2
and XTAL1. (The capacitors are internalD
no external capacitors are needed for the
oscillator to operate.) When not using the
internal oscillator this pin should be left
open.
XTAL1 (Pin 5) This is the crystal oscillator input. When us-
ing the internal oscillator, the crystal should
be tied between XTAL1 and XTAL2. XTAL1
can also be used as an input for an external
clock signal swinging from V
to V
. The
frequency of the crystal or the external
clock will be divided internally by the clock
divider as determined by the programming
voltage on pin 3.
CLK (Pin 6)
This is the filter clock pin. The clock signal
appearing on this pin is the filter clock
(f
CLK
). When using the internal crystal oscil-
lator or an external clock signal applied to
pin 5 while pin 7 is tied to V
, the CLK pin is
the output of the divider and can be used to
drive other LMF90s with its rail-to-rail output
swing. When not using the internal crystal
oscillator or an external clock on pin 5, the
CLK pin can be used as a CMOS or TTL
clock input provided that pin 7 is tied to
GND or V
. For best performance, the duty
cycle of a clock signal applied to this pin
should be near 50%, especially at higher
clock frequencies.
XLS (Pin 7)
This is a three-level logic pin. When XLS is
tied to V
, the crystal oscillator and fre-
quency divider are enabled and CLK (pin 6)
is an output. When XLS is tied to GND (pin
13), the crystal oscillator and frequency di-
vider are disabled and pin 6 is an input for a
clock swinging between V
and V
. When
XLS is tied to V
, the crystal oscillator and
frequency divider are disabled and pin 6 is a
TTL level clock input for a clock signal
swinging between GND and V
or between
V
and GND.
V
b
(Pin 8)
This is the negative power supply pin. It
should be bypassed with at least a 0.1
m
F
capacitor.
For
single-supply
connect this pin to system ground.
operation,
V
OUT
(Pin 9)
D (Pin 10)
This is the filter output.
This two-level logic input is used to set the
depth of the notch (the attenuation at f
0
).
When D is tied to GND or V
, the typical
notch depth is 48 dB or 39 dB, respective-
ly. Note, however, that the notch depth is
also dependent on the width setting (pin
1). See the Electrical Characteristics for
tested limits.
V
IN2
(Pin 11)
This is the input to the difference amplifier
section of the notch filter.
V
IN1
(Pin 12)
This is the input to the internal bandpass
filter. This pin is normally connected to pin
11. For wide bandwidth applications, an
anti-aliasing filter can be inserted between
pin 11 and pin 12.
GND (Pin 13)
This is the analog ground reference for the
LMF90. In split supply applications, GND
should
be
connected
ground. When operating the LMF90 from a
single positive power supply voltage, pin
13 should be connected to a ‘‘clean’’ refer-
ence voltage midway between V
and
V
.
to
the
system
V
a
(Pin 14)
This is the positive power supply pin. It
should be bypassed with at least a 0.1
m
F
capacitor.
1.0 Definition of Terms
A
max
:
the maximum amount of gain variation within the fil-
ter’s passband (See Figure 1 ). For the LMF90, A
Max
is
nominally equal to 0.25 dB.
A
min
:
the minimum attenuation within the notch’s stopband.
(SeeFigure 1 ). This parameter is adjusted by programming
voltage applied to pin 10 (D).
Bandwidth (BW) or Passband Width:
the difference in fre-
quency between the notch filter’s two cutoff frequencies.
Cutoff Frequency:
for a notch filter, one of the two fre-
quencies, f
C1
and f
C2
that define the edges of the pass-
band. At these two frequencies, the filter has a gain equal to
the passband gain.
f
CLK
:
the frequency of the clock signal that appears at the
CLK pin. This frequency determines the filter’s center fre-
quency. Depending on the programming voltage on pin 2
(R), f
CLK
will be either 33.33, 50, or 100 times the center
frequency of the notch.
f
0
or f
Notch
:
the center frequency of the notch filter. This
frequency is measured by finding the two frequencies for
which the gain
b
3 dB relative to the passband gain, and
calculating their geometrical mean.
Passband:
for a notch filter, frequencies above the upper
cutoff frequency (f
C2
inFigure 1 ) and below the lower cutoff
frequency (f
C1
in Figure 1 ).
10
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