Dual Universal Switched-Capacitor Filters

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Table 1. Filter Operating Modes

MODE

LP

HP

BP

N

LP-N*

HP-N*

COMMENTS

1

••

•

with identical sections cascaded, higher order Butterworth filters,

high-Q bandpass, low-Q notches.

1B

••

•

value.

2

••

•

less than the nominal value. Less sensitivity to resistor tolerances

than Mode 3.

2N

•

Extension of Mode 2 that allows higher frequencies. Highpass

and lowpass outputs are summed with external op amp and

two resistors. Good for lowpass elliptic filters.

3

••

•

Commonly used for multiple-pole Chebyshev filters, all-pole

higher order bandpass, lowpass, and highpass filters.

3A

••

•

•

•

Extension of Mode 3 that needs an external op amp and

two additional resistors. Commonly used for lowpass or higher

elliptic or Cauer filters.

*

LP-N = lowpass notch, HP-N = highpass notch. Both require an external op amp. See Definition of Terms (Table 2).

Table 2. Definition of Terms

TERM

DEFINITION

The clock frequency applied to the switched-capacitor filter.

frequency at the bandpass output.

The frequency of minimum amplitude response at the notch output.

Q

the amount of amplitude peaking at the lowpass and highpass outputs, but is not measured at these outputs.

The gain in V/V of the lowpass output at f

→0Hz.

The gain in V/V of the highpass output at f

The notch output gain as f

→0Hz.

LP-N

HP-N