Follow Us Part selection plays a vital role in any circuit design. Before the final go ahead is given for production to begin, it is very important to verify (through simulations and prototyping) if the right parts were selected.
How confident are you about having selected the right components for your design? How about having a tool to fine-tune your choices before the simulations?
The Analog Filter Wizard is one such hands-on design tool for real operational amplifiers. It ends your hunt for filter recommendations and aids in the design of low-pass, high-pass, or band-pass filters with the required specifications and with shorter lead times (Figure 1).
Figure 1. Filter type.
Additionally, it gives you critical analysis of the expected theoretical and practical performance of the filter.
So, how does this work? Are the recommendations just based on passband and stop-band definitions? No, you get a lot more than that. It encompasses the process from defining specifications all the way through to filter response characterization, as shown in Figure 2. This option lets you select the type of filter response (such as Butterworth, Bessel, Chebyshev, etc.), which defines the transition from the pass band to the stop band. It also enables you to choose between the fewer stage variants or fast settling variants.
Figure 2. Defining the specifications in Magnitude view.
With a variety of available views, such as Magnitude, Phase, Step Response, Power, and Noise, the tool allows you to check for incremental performance as you alter specifications. As shown in Figure 2 and Figure 3, the magnitude and phase views help you understand the effect of the phase and magnitude of the signal.
Figure 3. Phase view.
The Stages view shows the op amp filter stages and their characteristics (Figure 4). This view makes it easier to understand the filter stage by stage.
Figure 4. Filter stages.
The overshoot and ringing define the distortion of the waveforms, which can be analyzed with the step response of the filter obtained from the Step Response view (Figure 5).
Figure 5. Step Response of the filter.
After considering theoretical characteristics, the next step would be circuit design, which is shown in Figure 6. Here, the tool gives you recommendations based on the type of optimization specified (such as power, noise, or voltage range). You have the option of using the recommended part or choosing one of your own.
Figure 6. Component selection.
While the tool selects components with the values best suited to the specifications provided, it may be difficult or impractical to find and use the exact components recommended. Therefore, the Component Tolerances feature gives you the flexibility to choose your resistor and capacitor tolerances (Figure 7). Simultaneously, you can also view the effect of accommodating these tolerances on filter performance.
Figure 7. Defining the component tolerances.
Figure 8 shows the final circuit design incorporating the right amplifier so you can proceed to circuit simulations or prototyping.
Figure 8. Final circuit.
This tool adds significant value because it enables you to check for the incremental performance of the filter at every step, from defining the filter specifications to defining the tolerances. These features help you fine-tune your design at every step of the process. And they give you increased flexibility, which gives rise to optimal designs in fewer iterations, while saving valuable effort.
Follow the link below and go ahead try the tool for yourself!
analog.com/designtools/en/filterwizard/
Quiz:
Question 1:
Design a two stage, low-pass Butterworth filter with the following specifications: a cut-off frequency of 1 MHz, stop band of 3 MHz, and a gain of 0 dB. Optimize your design for low noise and a ±5 V supply. Use the default component tolerance and the amplifiers recommended by the tool.
What is the total quiescent power of the filter?
Question 2:
Design a two stage, low-pass, 4th-order Chebyshev filter with a pass-band ripple of 0.08 dB and 4th-order Butterworth filter with same specifications to compare them.
Which filter has the narrow transition band?
You can find the answer at the StudentZone blog.
