ML2111CIP datasheet(18/26 Pages) MICRO-LINEAR

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ML2111

OPERATION MODES (Continued)

The clock to center frequency ratio range is:

500

100

CLK

(mode 1c)

(6)

100

CLK

(mode 1b)

(7)

The input impedance of the S1 pin is clock dependent,

and in general R5 should not be larger than 5k

W for fCLK <

2.5MHz and 2k

W for fCLK > 2.5MHz. Mode 1c can be

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

beyond 100:1. The limit for the (fCLK/f0) ratio is 500:1 for

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

outputs whose frequency, fn, can be tuned independently

from the center frequency, f0. However, for all cases fn <

f0. These modes are useful when cascading second order

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

tune the center frequency below or above the fCLK/100 (or

fCLK/50) ratio. Mode 3 is a state variable configuration

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

CLK

100 50

()

;;

OHP

OLP

OBP

= -

;;

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

VIN

V-

SA/B

1 (20)

4 (17)

S1A

5 (16)

3 (18)

2 (19)

CLK

100 50

()

;

()

;

OHP

OBP

OLP

= -

;;

;

OLP

OHP

;

CLK

= ;

VIN

V-

SA/B

1 (20)

4 (17)

S1A

5 (16)

3 (18)

2 (19)

External

Op Amp

NOTCH

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