OPA340 datasheet(17/46 Pages) TI2

17 / 46 page

-20

-40

100

1 k

10 k

100 k

1 M

Frequency (Hz)

C = 1 F

C = 10 nF

C = 0

OPA340, OPA2340, OPA4340

www.ti.com

SBOS073C – SEPTEMBER 1997 – REVISED AUGUST 2016

Product Folder Links: OPA340 OPA2340 OPA4340

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Typical Applications (continued)

8.2.1.1 Design Requirements

When receiving low-level signals, limiting the bandwidth of the incoming signals into the system is often required.

The simplest way to establish this limited bandwidth is to place an RC filter at the noninverting terminal of the

amplifier, as shown in Figure 29. If a steeper attenuation level is required, a two-pole or higher-order filter may be

used.

8.2.1.2 Detailed Design Procedure

The design goals for this circuit include these parameters:

•

A noninverting gain of 10 V/V (20 dB)

•

Design a single-pole response circuit with –3-dB rolloff at 15.9 kHz and 159 Hz

•

Modify the design to increase attenuation level to –40 dB/decade (Sallen-Key Filter)

Use these design values:

•

C1 = 0 nF, 10 nF, 1 µF

•

R1 = 1 kΩ

•

RG = 10 kΩ

•

RF = 90 kΩ

Figure 30 shows how the output voltage of OPA340 changes over frequency depending on the value of C1 with a

constant R1 of 1 kΩ. Without any filtering of the input signal (C1 = 0), the –3-dB effective bandwidth is a function

of the OPA340 unity-gain bandwidth and closed-loop gain, f(–3dB) = UGBW/ACL, where ACL is closed-loop gain

and UGBW denotes unity-gain bandwidth. Thus, for a closed-loop gain = 10, f(–3dB) = 1 MHz/10 =100 kHz; see

Figure 30.

To further limit the output bandwidth, an appropriate choice of C1 must be made: for C1 = 10 nF,

= 15.9 kHz.

To further limit the bandwidth, a larger C1 must be used: choosing C1 = 1 µF,

= 159 Hz (see Figure 30).

8.2.1.3 Application Curve

Figure 30. OPA340 Single-Pole AC Gain vs Frequency Response

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