Rainbow-electronics MAX7491 Manual de usuario descargar pdf (Pagina 11)

MAX7490/MAX7491

Dual Universal Switched-Capacitor Filters

______________________________________________________________________________________ 11

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

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 f

CLK

ratios greater than the nominal value.

Mode 1B Design Equations

Mode 2

Figure 4 shows the configuration of Mode 2. Mode 2 is

a combination of Mode 1 and Mode 3. In this mode,

CLK

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.

HasfHz

Hatff

CLK

OLP

OBP

ON CLK

→=

−

100

()

(/)

HasfHz

Hatff

CLK

notch O

OLP

OBP

ON CLK

→=

−

100

()

(/)

∫ ∫

LPBPSN

COM

Figure 2. Mode 1, 2nd-Order Filter Providing Notch, Bandpass,

and Lowpass Outputs

∫ ∫

LPBPSN

R6 R5

COM

Figure 3. Mode 1B, 2nd-Order Filter Providing Notch, Bandpass,

and Lowpass Outputs

1 2 ... 6 7 8 9 10 11 12 13 14 15 16 17 18

MAX7490/MAX7491 1

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Rainbow-electronics MAX7491 Manual de usuario Pagina 11

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