Datasheet

MAX260/MAX261/MAX262
Microprocessor Programmable
Universal Active Filters
16 ______________________________________________________________________________________
Figures 7 through 11 show symbolic representations of
the MAX260 filter modes. Only one second-order sec-
tion is shown in each case. The A and B sections of
one MAX260/MAX261/MAX262 can be programmed for
different modes if desired. The f
0
, f
N
(notch), Q, and
various output gains in each case are shown in Table 5.
Filter Mode Selection
MODE 1 (Figure 7) is useful when implementing allpole
lowpass and bandpass filters such as Butterworth,
Chebyshev, Basset, etc. It can also be used for notch
filters, but only second-order notches because the rela-
tive pole and zero locations are fixed. Higher order
notch filters require more latitude in f
0
and 1
N
, which is
why they are more easily implemented with mode 3A.
1D
3
4
7
8
13
14
2D
3D
4D
6D
WR
5D
1Q
2Q
3Q
20
OCTAL D FLIP-FLOP
74HC374
V
CC
5Q
6Q
4Q
A0
A1
A2
D1
D2
A3
2
5
6
12
15
11011
-5V
9
OC
CKGND
MAX260
MAX261
MAX262
A0
A1
A2
A3
D2
D1
+5V
V
+
-5V
V
-
GND
WR
Figure 6. Buffering/Latching Logic Inputs
SCN
IN
SCN
N
BP
LP
+
-
-
MODE 1
+
-
∫ ∫
SCN
Σ
SCN = SWITCHED-CAPACITOR NETWORK
Figure 7. Filter Mode 1: Second-Order Bandpass, Lowpass,
and Notch
MODE
M1,
M0
FILTER
FUNCTIONS
f
0
Qf
N
H
OLP
H
OBP
H
ON1
(f ➝ 0)
H
ON2
(f ➝ f
CLK
/4)
OTHER
1 0, 0 LP, BP, N f
0
-1 -Q -1 -1
2 0, 1 LP, BP, N f
0
√2 -0.5 -Q/√2 -0.5 -1
3 1, 0 LP, BP, HP -1 -Q H
OHP
= -1
-1 -Q H
OHP
= -1
4 1, 1 LP, BP, AP
SEE TABLE 2 SEE TABLE 3
-2 -2Q
H
OAP
= -1
f
Z
= f
0
, Q
Z
= Q
Table 5. Filter Modes for Second-Order Functions
Notes: f
0
= Center Frequency
f
N
= Notch Frequency
H
OLP
= Lowpass Gain at DC
H
OBP
= Bandpass Gain at f
0
H
OHP
= Highpass Gain as f approaches f
CLK
/4
H
ON1
= Notch Gain as f approaches DC
H
ON2
= Notch Gain as f approaches fCLK/4
H
OAP
= Allpass Gain
f
z
, Q
z
= f and Q of Complex Pole Pair
+
R
R
G
H
+
R
R
G
L
f
R
R
H
L
0