ML2111

18

The clock to center frequency ratio range is:

500

1

100

1

50

1

0

˜˜

f

f

or

CLK

(mode 1c)

(6)

100

1

50

1

100

2

50

2

0

or

f

f

or

CLK

˜˜

(mode 1b)

(7)

The input impedance of the S1 pin is clock dependent,

and in general R5 should not be larger than 5k

2.5MHz and 2k

used to increase the clock-to-center-frequency ratio

this mode. The filter will exhibit large output offsets with

larger ratios. Mode 1d (Figure 19) is the fastest mode of

operation: center frequencies beyond 20kHz can easily

be achieved at a 50:1 ratio.

Modes 2, 2a, and 2b (Figures 20, 21, and 22) have notch

functions to create an overall elliptic highpass, bandpass

or notch response. The input amplifier and its feedback

resistors R2 and R4 are now part of the resonant loop.

Because of this, mode 2 and its derivatives are slower

than mode 1 and its derivatives.

In Mode 3 (Figure 23) a single resistor ratio, R2/R4, can

since it provides a highpass, bandpass, lowpass output

through progressive integration. Notches are acquired by

summing the highpass and lowpass outputs (mode 3a,

Figure 24). The notch frequency can be tuned below or

Figure 24. Mode 3a: 2nd Order Filter Providing Highpass, Bandpass, Lowpass, Notch — ½ ML2111

f

f

R2

R

Q

R3

R2

R2

R

CLK

0

100 50

4

4

=™

=

™

()

;;

H

R2

R

H

R

R

H

R3

R

OHP

OLP

OBP

=-

=-

= -

1

4

11

;;

Figure 23. Mode 3: 2nd Order Filter Providing Highpass, Bandpass, Lowpass — ½ ML2111

LP

V-

R1

6

15

1 (20)

R3

R2

4 (17)

R4

+

Σ

BP

5 (16)

HP

3 (18)

2 (19)

Q

R2

R

R3

R2

=™

4

f

f

R2

R

f

f

R

R

CLK

n

CLK

h

l

0

100 50

4

100 50

=™

=™

()

;

()

;

H

R2

R

H

R3

R

H

R

R

OHP

OBP

OLP

= -

=-

=-

11

4

1

;;

;

Hf

f

Q

R

R

H

R

R

H

ON

g

l

OLP

g

h

OHP

==

™

™

-

™









0

16

;

Hf

f

R

R

R2

R

ON

CLK

g

h

2

21

“







Hf

R

R

R

R

ON

g

l

1

0

4

1

“=

™

16

LP

V-

R1

6

15

1 (20)

R3

R2

4 (17)

R4

+

Σ

BP

5 (16)

HP

3 (18)

2 (19)

External

Op Amp

NOTCH