OPA830IDR datasheet(22/35 Pages) TI

22 / 35 page

OPA830

SBOS263F − AUGUST 2004 − REVISED AUGUST 2008

www.ti.com

SINGLE-SUPPLY ACTIVE FILTER

The OPA830, while operating on a single +3V or +5V

supply, lends itself well to high-frequency active filter

designs. Again, the key additional requirement is to

establish the DC operating point of the signal near the

supply midpoint for highest dynamic range. Figure 8

shows an example design of a 1MHz low-pass Butterworth

filter using the Sallen-Key topology.

Both the input signal and the gain setting resistor are

AC-coupled using 0.1

µF blocking capacitors (actually

giving bandpass response with the low-frequency pole set

to 32kHz for the component values shown). As discussed

for Figure 1, this allows the midpoint bias formed by the

two 1.87k

Ω resistors to appear at both the input and output

pins. The midband signal gain is set to +4 (12dB) in this

case. The capacitor to ground on the noninverting input is

intentionally set larger to dominate input parasitic terms. At

a gain of +4, the OPA830 on a single supply will show

30MHz small- and large-signal bandwidth. The resistor

values have been slightly adjusted to account for this

limited bandwidth in the amplifier stage. Tests of this circuit

show a precise 1MHz, −3dB point with a maximally-flat

passband (above the 32kHz AC-coupling corner), and a

maximum stop band attenuation of 36dB at the amplifier’s

−3dB bandwidth of 30MHz.

DESIGN-IN TOOLS

DEMONSTRATION BOARDS

Two printed circuit boards (PCBs) are available to assist

in the initial evaluation of circuit performance using the

OPA830 in its two package options. Both of these are

offered free of charge as unpopulated PCBs, delivered

with a user’s guide. The summary information for these

fixtures is shown in Table 1.

Table 1. Demonstration Fixtures by Package

ORDERING

LITERATURE

PRODUCT

PACKAGE

ORDERING

NUMBER

LITERATURE

NUMBER

OPA830ID

SO-8

DEM

-OPA-SO-1A

SBOU009

OPA830IDBV

SOT23-5

DEM

-OPA-SOT-1A

SBOU010

The demonstration fixtures can be requested at the Texas

Instruments web site (www.ti.com) through the OPA830

product folder.

OPA830

1.5k

Ω

1.87k

Ω

500

Ω

+5V

1.87k

Ω

150pF

0.1

µF

1MHz, 2nd−Order

Butterworth Filter

100pF

432

Ω

137

Ω

0.1

µF

Figure 8. Single-Supply, High-Frequency Active Filter

OPA830IDR Datasheet(PDF) 22 Page - Texas Instruments

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