UAF42AP datasheet(5/16 Pages) TI2

5 / 16 page

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UAF42

www.ti.com

SBFS002B – JULY 1992 – REVISED OCTOBER 2010

APPLICATION INFORMATION

The UAF42 is a monolithic implementation of the

The

basic

building

element

the

most

proven state-variable analog filter topology. This

commonly-used

filter

types

the

second-order

device is pin-compatible with the popular UAF41

section. This section provides a complex-conjugate

analog filter, and it provides several improvements.

pair of poles. The natural frequency, wn, and Q of the

pole pair determine the characteristic response of the

The slew rate of the UAF42 has been increased to

section. The low-pass transfer function is shown in

10V/ms,

versus

1.6V/ms

for

the

UAF41.

Equation 1:

Frequency • Q product of the UAF42 has been

improved, and the useful natural frequency extended

by a factor of four to 100kHz. FET input op amps on

(1)

the UAF42 provide very low input bias current. The

monolithic construction of the UAF42 provides lower

The

high-pass

transfer

function

given

cost and improved reliability.

Equation 2:

DESIGN PROGRAM

(2)

Application report SBFA002 (available for download

The band-pass transfer function is calculated using

at www.ti.com) and a computer-aided design program

Equation 3:

also available from Texas Instruments, make it easy

to design and implement many kinds of active filters.

The DOS-compatible program guides you through the

(3)

design

process

and

automatically

calculates

component values.

A band-reject response is obtained by summing the

low-pass and high-pass outputs, yielding the transfer

Low-pass, high-pass, band-pass and band-reject

function shown in Equation 4:

(notch) filters can be designed. The program supports

the three most commonly-used all-pole filter types:

Butterworth, Chebyshev and Bessel. The less-familiar

(4)

inverse Chebyshev is also supported, providing a

smooth passband response with ripple in the stop

The most common filter types are formed with one or

band.

more cascaded second-order sections. Each section

is designed for wn and Q according to the filter type

With each data entry, the program automatically

(Butterworth, Bessel, Chebyshev, etc.) and cutoff

calculates and displays filter performance. This

frequency. While tabulated data can be found in

feature allows a spreadsheet-like what-if design

virtually any filter design text, the design program

approach. For example, a user can quickly determine,

eliminates this tedious procedure.

by trial and error, how many poles are required for a

desired attenuation in the stopband. Gain/phase plots

Second-order

sections

may

noninverting

may be viewed for any response type.

(Figure 1) or inverting (Figure 2). Design equations

for these two basic configurations are shown for

reference.

The

design

program

solves

these

equations,

providing

complete

results,

including

component values.

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