Elektor_Mag_-_January-February_2021

78 January & February 2021 http://www.elektormagazine.com

With the Cauer filter the minimum attenuation in the stop band

is another additional parameter. The notches provide a much

steeper transition in the stop band, but the curve then returns

to a lower attenuation. The number of notches corresponds to

the number of resonant circuits in the circuit (as these have

different frequencies). Figure 9 shows a seventh-order Cauer

low-pass filter with a minimum attenuation of 40 dB. Table 1

lists the component values for a minimum attenuation of 40,

50, 60 and 70 dB.

Figure 10 shows the frequency responses of all four of the Cauer

low-pass filters. The height of the ‘bumps’ corresponds to the

Figure 7: Frequency response of seventh-order, 1 MHz Chebyshev low-pass
filters with a ripple in the pass-band of 0.1 dB (brown), 0.5 dB (blue), 1 dB
(green) and 3 dB (red).

Figure 10: Frequency responses of seventh-order, 1-MHz Cauer low-pass
filters with a minimum attenuation of 40, 50, 60 and 70 dB.

Figure 11: Close-up of the pass-band from Figure 10 with a minimum

attenuation of 40 dB (brown), 50 dB (blue), 60 dB (green) and 70 dB (red).

Figure 8: A close-up of the pass-band from Figure 7. The corner frequency

corresponds to the point on the curve where the amplitude drops below the

defined ripple. Ripple: 0.1 dB (brown), 0.5 dB (blue), 1 dB (green) and 3 dB

(red).

L1

790

L2

338

C 4

4n62

C 5

4n71

C 6

3n58

R 2

50

R 1

50

200522-009

L2

437

C 7

3n01

C 1

1n10

C 2

6n56

C 3

4n27

Figure 9: Seventh-order Cauer low-pass filter with a ripple of 0.5 dB in the
pass-band and a minimum attenuation of 40 dB. The component values for
other levels of attenuation are shown in Table 1.