MAX7490EEE(2000) 查看數據表（PDF） - Maxim Integrated
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MAX7490EEE Datasheet PDF : 18 Pages
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Dual Universal Switched-Capacitor Filters
CC
R3
R2
N
S
BP
LP
R1
VIN
-
+
Σ
∫
∫
COM
Figure 2. Mode 1, 2nd-Order Filter Providing Notch, Bandpass,
and Lowpass Outputs
have to track Q). The notch and bandpass center fre-
quencies are identical. The notch output gain is the
same above and below the notch center frequency.
Mode 1 can also be used to make high-order Butter-
worth lowpass filters, low Q notches, and multiple-order
bandpass filters obtained by cascading identical
switched-capacitor sections.
Mode 1 Design Equations
fO = fCLK
100
fnotch = fO
Q = R3
R2
HOLP = −R2
R1
HOBP = −R3
R1
HON1(as f → 0Hz) = −R2
R1
HON2 (at f = fCLK / 2) = −R2
R1
Mode 1B
Figure 3 shows the configuration of Mode 1B. R5 and
R6 are added to lower the feedback voltage from the
lowpass output to the summing input. This allows the
clock-to-center frequency to be adjusted beyond the
nominal value. This mode essentially has the same
functions and speed as Mode 1 while providing a high-
Q with fCLK/fO ratios greater than the nominal value.
CC
R6
R5
R3 COM
R2
N
S
BP
LP
R1
VIN
-
+
Σ
∫
∫
COM
Figure 3. Mode 1B, 2nd-Order Filter Providing Notch, Bandpass,
and Lowpass Outputs
Mode 1B Design Equations
fO = fCLK
100
fn = fO
R6
R6 + R5
Q = R3 R6
R2 R6 + R5
HOLP = −R2 R6 + R5
R1 R6
HOBP = −R3
R1
HON1(as f → 0Hz) = −R2
R1
HON2 (at f = fCLK / 2) = −R2
R1
Mode 2
Figure 4 shows the configuration of Mode 2. Mode 2 is
a combination of Mode 1 and Mode 3. In this mode,
fCLK/fO is always less than the part’s nominal ratio.
However, it provides less sensitivity to resistor toler-
ances than does Mode 3. It has a highpass notch out-
put where the notch frequency depends solely on the
clock frequency.
______________________________________________________________________________________ 11
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