LTC1067-50_15 Datasheet, PDF (10/20 Pages) Linear Technology – Rail-to-Rail, Very Low Noise Universal Dual Filter Building Block

LTC1067/LTC1067-50
W
U
ODES OF OPERATIO
C_C
R6
R5
R3
R1
V_IN
R2
–
+
AGND
NOTE: RATIO = 100 FOR LTC1067
= 50 FOR LTC1067-50
N
S
BP
LP
+
–
Σ
∫
∫
1067 F04
√ ^fO
=
f_CLK
RATIO
R6 _;
(R6 + R5)
f_n
=
f_O
√ ^Q
=
R3
R2
(R6R+6R5);
H_ON
=
–
RR21;
H_OBP
=
–
R3
R1
( ) ^HOLP
=
–
R2
R1
R6 + R5
R6
Figure 4. Mode 1b, 2nd Order Filter Providing Notch,
Bandpass and Lowpass Outputs
The parallel combination of R5 and R6 should be kept
below 5k.
Please refer to the Operating Limits paragraph under Appli-
cations Information for a guide to the use of capacitor C_C.
Mode 3
In Mode 3, the ratio of the external clock frequency to the
center frequency of each 2nd order section can be ad-
justed above or below the part’s nominal ratio. Figure 5
illustrates Mode 3, the classical state variable configura-
tion, providing highpass, bandpass and lowpass 2nd
order filter functions. Mode 3 is slower than Mode 1. Mode
3 can be used to make high order all-pole bandpass,
lowpass and highpass filters.
Please refer to the Operating Limits paragraph under Appli-
cations Information for a guide to the use of capacitor C_C.
Mode 2
Mode 2 is a combination of Mode 1 and Mode 3, shown in
Figure 6. With Mode 2, the clock-to-center frequency ratio,
f_CLK/f_O, is always less than the part’s nominal ratio. The
advantage of Mode 2 is that it provides less sensitivity to
resistor tolerances than does Mode 3. Mode 2 has a
highpass-notch output where the notch frequency
depends solely on the clock frequency and is therefore
less than the center frequency, f_O.
Please refer to the Operating Limits paragraph under Appli-
cations Information for a guide to the use of capacitor C_C.
C_C
R1
V_IN
AGND
R4
R3
R2
HP S
BP
LP
–
+
–
Σ
∫
∫
+
1067 F05
√ ^{( )√} _{( )} ^fO
=
f_CLK
RATIO
R2
R4
;
Q
=
1.005
R3
R2
R2
R4
1
1
–
R3
(RATIO)(0.32)(R4)
( ) ^HOHP
=
–
R2
R1
;
H_OBP
=
–
R3
R1
1
1
–
R3
(RATIO)(0.32)(R4)
;
H_OLP
=
–
R4
R1
NOTE: RATIO = 100 FOR LTC1067
= 50 FOR LTC1067-50
Figure 5. Mode 3, 2nd Order Section Providing
Highpass, Bandpass and Lowpass Outputs
R1
V_IN
AGND
R4
R3
R2
–
+
C_C
HPN S
+
–
Σ
∫
BP
LP
∫
1067 F06
√ ^fO
=
f_CLK
RATIO
1
+
R2
R4
;
f_n
=
f_CLK
RATIO
( ) _{√ ( )} ^Q
=
1.005
R3
R2
1 + ^R2
R4
1
1
–
R3
(RATIO)(0.32)(R4)
( ) ^HOHPN
=
–
R2
R1
(AC
GAIN,
f
>>
f_O);
H_OHPN
=
–
R2
R1
1
1
+
R2
R4
(DC GAIN)
( ) ( ) ^HOBP
=
–
R3
R1
1
1
–
R3
(RATIO)(0.32)(R4)
;
H_OLP
=
–
R2
R1
1
1
+
R2
R4
NOTE: RATIO = 100 FOR LTC1067
= 50 FOR LTC1067-50
Figure 6. Mode 2, 2nd Order Filter Providing Highpass
Notch, Bandpass and Lowpass Outputs
10