FilterPro用户指南：简化模拟滤波器设计

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"TI滤波器设计文档是Texas Instruments（TI）发布的一份用户指南，主要针对FilterPro程序的使用，该程序旨在简化采用多反馈（MFB）和萨伦-基（Sallen-Key）拓扑结构的有源滤波器的设计与验证过程。这份文档详细介绍了设计师在使用FilterPro时需要输入的信息以及程序能提供的服务。" 在这份用户指南中，TI详细阐述了滤波器设计的关键概念和技术，包括： 1. **滤波器类型定义**（Filter Type Definitions）：文档可能涵盖了不同类型的滤波器，如低通、高通、带通、带阻滤波器等，这些滤波器在电子系统中有着广泛的应用。 2. **滤波器响应**（Filter Responses）：这部分内容可能详细解释了各种滤波器的频率响应特性，如截止频率、通带增益、阻带衰减等，以及它们如何影响信号处理。 3. **电路实现**（Circuit Implementation）：TI可能提供了MFB和Sallen-Key拓扑结构的电路实现细节，这两种拓扑结构因其灵活性和设计简单性在有源滤波器设计中常用。 4. **使用FilterPro Desktop v3.1**：这部分介绍了如何操作FilterPro软件，包括创建新设计、调整参数和分析滤波器性能。 5. **在FilterPro Desktop中更改组件**：指南可能教导用户如何修改滤波器电路中的电容、电阻等元件值，以优化滤波器的性能。 6. **电容器选择**（Capacitor Selection）：讨论了如何根据设计需求选择合适的电容器，包括电容值、稳定性、温度系数等因素。 7. **运算放大器选择**（OpAmp Selection）：TI可能会提供关于选择适合滤波器应用的运算放大器的建议，考虑因素包括增益、带宽、噪声和电源电压范围等。 8. **UAF42通用有源滤波器**：介绍了一个特定的集成芯片，UAF42，它是一个用于构建各种滤波器的通用组件。 9. **设计工具**（Design Tools）：可能包含了一些辅助设计的工具或功能，比如滤波器性能的仿真工具、优化工具等。 10. **从FilterPro v2.0.3迁移设计**：对于已经使用旧版本FilterPro的用户，这部分将指导他们如何无缝过渡到新版本，并保持原有设计的兼容性。 11. **重要注意事项**（Important Notes）：提请注意在设计和实施过程中可能出现的问题和解决方法，以避免常见错误。 12. **结论**（Conclusion）：总结了FilterPro的主要优点和价值，以及它如何提升滤波器设计的效率。此外，文档中还包含了多个插图，如各种滤波器的频率响应曲线，帮助用户直观理解滤波器的行为。通过这份详尽的指南，工程师可以有效地利用FilterPro来设计满足特定要求的高性能模拟滤波器，从而加速产品开发进程并确保设计质量。

FILTER RESPONSE vs FREQUENCY

Normalized Frequency

Filter Response (dB)

+10

10-

f /100

f /10

10f

5-Pole Chebyshev

3dB Ripple

Ripple

FILTER RESPONSE vs FREQUENCY

Normalized Frequency

Filter Response (dB)

4-Pole Chebyshev

3dB Ripple

Ripple

+10

10-

f /100

f /10

10f

www.ti.com

Filter Responses

2 Filter Responses

An ideal low-pass filter would completely eliminate signals above the cutoff frequency, and perfectly pass

signals below the cutoff (in the passband). This ideal, brick-wall response is shown in Figure 1 through

Figure 4. In real filters, various tradeoffs are made attempting to approximate the ideal. Some filter

responses are optimized for gain flatness in the passband; some trade off gain variation (ripple) in the

passband for steeper roll-off; still others trade off both flatness and rate of roll-off in favor of

pulse-response fidelity. FilterPro supports several commonly-used filter responses: Butterworth,

Chebyshev, Bessel, Gaussian, and Linear-Phase.

2.1 Butterworth (Maximally Flat Magnitude)

This filter has the flattest possible passband magnitude response. Attenuation is –3dB at the design cutoff

frequency. Attenuation above the cutoff frequency is a moderately steep –20dB per decade per pole. The

pulse response of the Butterworth filter has moderate overshoot and ringing. It has good all-around

performance. Its pulse response is better than Chebyshev, and its rate of attenuation is better than that of

Bessel.

2.2 Chebyshev (Equal Ripple Magnitude)

Note: Mr. Chebyshev's name is also transliterated Tschebychev, Tschebyscheff, or Tchevysheff.

This filter response has steeper attenuation above the cutoff frequency than Butterworth. This advantage

comes at the penalty of amplitude variation (ripple) in the passband. Unlike Butterworth and Bessel

responses, which have 3dB attenuation at the cutoff frequency, the Chebyshev cutoff frequency is defined

as the frequency at which the response falls below the ripple band. For even-order filters, all ripple is

above the 0dB-gain dc response, so cutoff is at 0dB (as Figure 5 shows). For odd-order filters, all ripple is

below the 0dB-gain dc response, so cutoff is at –(ripple)dB, as Figure 6 illustrates. For a given number of

poles, a steeper cutoff can be achieved by allowing more passband ripple. The Chebyshev has

considerable ringing in its pulse response compared to the Butterworth type.

space

Figure 6. Response vs Frequency of Odd-Order

Figure 5. Response vs Frequency of Even-Order

(Five-Pole), 3dB Ripple Chebyshev Filter Showing

(Four-Pole), 3dB Ripple Chebyshev Filter Showing

Cutoff at –3dB

Cutoff at 0dB

SBFA001C–June 1991–Revised February 2011 FilterPro™ User's Guide

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Circuit Implementation

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2.3 Bessel (Maximally Flat Time Delay)

Also called the Thomson filter, this filter has excellent pulse response (that is, minimal overshoot and

ringing) due to its linear phase response. These filter types are often used in audio crossover systems.

Analog Bessel filters are characterized by almost constant group delay across the entire passband, thus

preserving the wave shape of filtered signals in the passband. For a given number of poles, its magnitude

response is not as flat, nor is its attenuation beyond the –3dB cutoff frequency as steep as the

Butterworth. Although it takes a higher-order Bessel filter to give a magnitude response which approaches

that of a given Butterworth filter, the pulse response fidelity of the Bessel filter may make the added

complexity (because of the need for additional filter sections) worthwhile.

2.4 Gaussian (Minimum Group Delay)

This type of filter has an impulse response that is a Gaussian function. Gaussian filters are designed to

give no overshoot to a step function input while minimizing the rise and fall time. This behavior is closely

connected to the fact that the Gaussian filter has the minimum possible group delay.

2.5 Linear-Phase (Equi-Ripple Delay)

Similar to the Bessel response, this filter response has a phase response that is a linear function of the

frequency. While the Bessel has a maximally-flat time delay, these filters approximate linear phase to

within a given ripple (0.5 degrees or 0.05 degrees). They have a sharper magnitude response than the

Bessel filter, sometimes allowing for a lower-order filter to be used to achieve a desired attenuation at a

specific frequency. The step response has slightly more overshoot than Bessel filters.

3 Circuit Implementation

Even-order filters designed with this program consist of cascaded sections of complex pole-pairs.

Odd-order filters contain an additional real-pole section. Figure 7 through Figure 11 show the

recommended cascading arrangement. The figures show the additional real-pole section ahead of the

other sections, but some configurations are better with the real-pole section following (see Figure 16). The

program automatically places lower Q stages ahead of higher Q stages to prevent op amp output

saturation due to gain peaking. The program can be used to design low-pass, high-pass, and all-pass

filters up to the 10th order. Bandpass and bandstop filters up to the 20th order may also be designed with

FilterPro since each low-pass pole-zero pair can be transformed into a second-order stage.

Table 1 lists the filter order and relevant example circuit.

Table 1. Filter Circuit vs Filter Order

Filter Order Figure

One pole Figure 7

Two poles Figure 8

Three poles Figure 9

Four or more poles (even order) Figure 10

Five or more poles (odd poles) Figure 11

FilterPro™ User's Guide SBFA001C–June 1991–Revised February 2011

Submit Documentation Feedback

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