Datasheet

10
LTC1067/LTC1067-50
ODES OF OPERATIO
U
W
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
.
–
+
Σ
∫ ∫
AGND
R1
HP
BP
LP
V
IN
1067 F05
+
–
S
R2
R3
C
C
R4
f
O
=
f
CLK
RATIO
H
OHP
= – ; H
OBP
= – ;
NOTE: RATIO = 100 FOR LTC1067
= 50 FOR LTC1067-50
R2
R1
R3
R1
R4
R1
H
OLP
= –
R3
R2
√
R2
R4
R3
(RATIO)(0.32)(R4)
( )
1
1 –
R3
(RATIO)(0.32)(R4)
( )
1
1 –
( )
√
R2
R4
; Q = 1.005
Figure 5. Mode 3, 2nd Order Section Providing
Highpass, Bandpass and Lowpass Outputs
Figure 6. Mode 2, 2nd Order Filter Providing Highpass
Notch, Bandpass and Lowpass Outputs
–
+
Σ
∫ ∫
AGND
R1
N
BP
LP
V
IN
1067 F04
+
–
S
R2
R3
C
C
R5R6
f
O
= ; f
n
= f
O
Q = ; H
ON
= – ; H
OBP
= –
H
OLP
= –
R2
R1
R3
R1
R3
R2
f
CLK
RATIO
√
R6
(R6 + R5)
R2
R1
R6 + R5
R6
√
R6
(R6 + R5)
()
NOTE: RATIO = 100 FOR LTC1067
= 50 FOR LTC1067-50
Figure 4. Mode 1b, 2nd Order Filter Providing Notch,
Bandpass and Lowpass Outputs
–
+
Σ
∫ ∫
AGND
R1
HPN
BP
LP
V
IN
1067 F06
+
–
S
R2
R3
C
C
R4
f
O
= ; f
n
=
f
CLK
RATIO
√
R2
R4
1 +
f
CLK
RATIO
Q = 1.005
R3
R2
( )
√
R2
R4
1 +
H
OHPN
= – (AC GAIN, f >> f
O
); H
OHPN
= –
R2
R1
R2
R1
R2
R1
1
R2
R4
1 +
( )
(DC GAIN)
H
OBP
= –
R3
R1
; H
OLP
= –
NOTE: RATIO = 100 FOR LTC1067
= 50 FOR LTC1067-50
R3
(RATIO)(0.32)(R4)
( )
1
1 –
R3
(RATIO)(0.32)(R4)
( )
1
1 –
1
R2
R4
1 +
( )