OPA2140AIDR datasheet(23/48 Pages) TI

23 / 48 page

8 Application and Implementation

Note

Information in the following applications sections is not part of the TI component specification,

and TI does not warrant its accuracy or completeness. TI’s customers are responsible for

determining suitability of components for their purposes, as well as validating and testing their design

implementation to confirm system functionality.

8.1 Application Information

The OPA140, OPA2140, and OPA4140 are unity-gain stable, operational amplifiers with very low noise, input

bias current, and input offset voltage. Applications with noisy or high-impedance power supplies require

decoupling capacitors placed close to the device pins. In most cases, 0.1-μF capacitors are adequate. Designers

can easily use the rail-to-rail output swing and input range that includes V– to take advantage of the low-noise

characteristics of JFET amplifiers while also interfacing to modern, single-supply, precision data converters.

8.2 Typical Application

OPA140

Output

Input

590

2.94 k

499

39 nF

1 nF

Figure 8-1. 25-kHz Low-pass Filter

8.2.1 Design Requirements

Lowpass filters are commonly employed in signal processing applications to reduce noise and prevent aliasing.

The OPAx140 are an excellent choice to construct high-speed, high-precision active filters. Figure 8-1 shows a

second-order, low-pass filter commonly encountered in signal processing applications.

Use the following parameters for this design example:

• Gain = 5 V/V (inverting gain)

• Low-pass cutoff frequency = 25 kHz

• Second-order Chebyshev filter response with 3-dB gain peaking in the passband

8.2.2 Detailed Design Procedure

The infinite-gain multiple-feedback circuit for a low-pass network function is shown in. Use Equation 1 to

calculate the voltage transfer function.

1 3

1 R R C C

Output

Input

s C

1 R

1 R R C C

(1)

This circuit produces a signal inversion. For this circuit, the gain at DC and the lowpass cutoff frequency are

calculated by Equation 2:

Gain

1 R R C C

(2)

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OPA140, OPA2140, OPA4140

SBOS498E – JULY 2010 – REVISED JULY 2021

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