LMF100_15 Datasheet, PDF (18/40 Pages) Texas Instruments – LMF100 Dual High-Performance Switched Capacitor Filters

LMF100
SNOSBG9B – JULY 1999 – REVISED JUNE 2015
Device Functional Modes (continued)
8.4.1.3 MODE 1b: Notch 1, Bandpass, Lowpass Outputs:
f_notch = f₀ (See Figure 42)
f₀
=
center
frequency
of
the
complex
pole
pair
=
f_CLK
100
´
2 or ^fCLK ´
50
2
f_notch = center frequency of the imaginary zero pair = f₀
H_OLP
=
Lowpass
gain
(as
f
®
0)
=
R2
-
R1
H_OBP
=
Bandpass
gain
(at
f
®
0)
=
R3
-
R1
H_ON = Notch output gain as
f ®0
f ® f_CLK / 2
= ^-R2
R₁
Q
=
f₀
BW
=
R3
R2
= quality
factor
of
the complex pole pair
BW = the - 3 dB bandwidth of the bandpass output.
Circuit dynamics:
H_OLP = ^HOBP or H_OBP = H_OLP ´ Q = 2
2Q
H_OBP = ^{HON ´ Q}
2
H_OLP(peak) @ Q ´ H_OLP (for high Q ' s)
8.4.1.4 MODE 2: Notch 2, Bandpass, Lowpass: f_notch < f₀ (See Figure 43)
f₀
=
center
frequency
=
f_CLK
100
´
R2 _{+ 1 or} f_{CLK ´}
R4
50
R2 _{+ 1}
R4
f_notch
=
f_CLK
100
or
f_CLK
50
Q = quality factor of the complex pole pair = ^{R2 / R4 + 1}
R2 / R3
H_OLP
=
Lowpass
output
gain (as
f
®
0)
=
R2 / R1
-
R2 / R4 + 1
H_OBP = Bandpass gain (at f ® f₀ ) = -R3 / R1
H_ON1
=
Notch
output
gain (as
f
®
0)
=
R2 / R1
-
R2 / R4 + 1
H_ON1
=
Notch
output
gain
æ
ç ^as
è
f
®
f_CLK
2
ö
÷
ø
=
- R2 / R1
Filter dynamics : H_OBP = Q H_OLP H_ON2 = H_OLP1 H_ON2
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