OPA189 Datasheet, PDF (22/34 Pages) Texas Instruments – Precision, 36-V, 14-MHz, MUX-Friendly Low-Noise, Rail-to-Rail Output, Zero-Drift Operational Amplifiers

OPA189, OPA2189, OPA4189
SBOS830 – JUNE 2017
9.2.2 25-kHz Low-pass Filter
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Input
R4
2.94 k
R1
590
R3
499
C2
39 nF
C5
1 nF
±
+
OPAx189
Output
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Figure 12. 25-kHz Low-pass Filter
9.2.2.1 Design Requirements
Low-pass filters are commonly employed in signal processing applications to reduce noise and prevent aliasing.
The OPAx189 devices are ideally suited to construct high-speed, high-precision active filters. Figure 12 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
9.2.2.2 Detailed Design Procedure
The infinite-gain multiple-feedback circuit for a low-pass network function is shown in Figure 12. Use Equation 1
to calculate the voltage transfer function.
Output _s
Input
s²
1 R₁R₃C₂C₅
s C₂ 1 R₁ 1 R₃ 1 R₄ 1 R₃R₄C₂C₅
(1)
This circuit produces a signal inversion. For this circuit, the gain at DC and the low-pass cutoff frequency are
calculated by Equation 2:
Gain ^R4
R₁
f_C
1
2S
1 R₃R₄C₂C₅
(2)
Software tools are readily available to simplify filter design. WEBENCH^® Filter Designer is a simple, powerful,
and easy-to-use active filter design program. The WEBENCH® Filter Designer lets the user create optimized
filter designs using a selection of TI operational amplifiers and passive components from TI's vendor partners.
Available as a web based tool from the WEBENCH Design Center, WEBENCH Filter Designer allows board-level
designers to create, optimize, and simulate complete multistage active filter solutions within minutes.
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Product Folder Links: OPA189 OPA2189 OPA4189