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10

Component

Value

Ideal

Pre-distorted

238

Ω

211

Ω

67pF

3.01k

Ω

314

Ω

300

Ω

67pF

953

Ω

953

Ω

108

Ω

100

Ω

1.06k

Ω

1.07k

Ω

22pF

100pF

3.01k

Ω

256

Ω

227

Ω

256

Ω

227

Ω

900

Ω

850

Ω

22pF

100pF

953

Ω

953

Ω

Table 1: Filter Component Values

The nearest standard values for capacitors and resistors

were used to build this filter. The resistors were 1%

tolerance, and the capacitors 5% tolerance. The ideal

and measured gains are shown in Figure 8.

Figure 8: Lowpass Anti-aliasing Filter Response

To change the cutoff frequency of this filter, do the following:

s

Determine the new cutoff frequency:

bandwidth of the CLC418

s

Scale (multiply) all frequency specifications and

s

Make sure that your system requirements are met

s

s

Set the resistors to the Ideal Values in the table

above (the pre-distorted values

do not linearly

scale with frequency)

For more information on the design of Sallen-Key filters and

filter pre-distortion, see Comlinear’s App Notes on filters.

Precision Full-Wave Rectifier

Figure 9 shows a precision full-wave rectifier using the

all inverting gain is achieved. The output voltage of the

rectifier is:

Figure 9: Precision Full-Wave Rectifier

minimize delay.

Calculate the ratio:

values up to this point.

Frequency (MHz)

418 Fig8

0

-30

-20

-10

-60

1

10

-40

-50

Measured

Ideal

V

R

R

R

R

1

R

R

R

1

R

R

R

R

R

R

V ,V

0

V ,V

0

o

2

5

7

1

2

5

3

4

6

2

1

7

5

in

in

in

in

=

+

+









+

+









⋅ +









⋅

⋅

>



























⋅

<

-

+

20

Ω

1/2

CLC418

418 Fig9

-

+

1/2

CLC418

U1a

U1b

V

V

G G

V

0

o

in

1

2

in

=

>

,

R

R

1+

R

R

1

1

G

1

R

R

G

R

R

R

R

R

R

G

4

6

7

2

2

2

3

2

7

3

7

3

2

3

2

=

+









− +









−

+

⋅

f

f

10

c(new)

3dB(418)

≤