In the previous tech note, we discussed how to call Precision Studio's Filter Wizard tool from Signal Chain Designer. While Filter Wizard doesn't have the capability to build differential filters, it can still be used to help guide the design of more complex filters in Signal Chain Designer. We'll walk through how in the final section of this tech note.
Start your filter design by dragging the Low Pass Filter Block into the signal chain area. Then click the Single Stage option after the prompt comes up to start building your filter in Signal Chain Designer.
Filter Design Options in Signal Chain Designer
Next, you'll have the option to select the type of filter which includes single ended to differential and fully differential options. The filter can be selected as a first or second order design using the Specifications tab. This is where you'll be able to set the bandwidth, gain, and Q (second order) of the filter. For further help with the filter design process, there is a training video available.
Selecting Filter Type in Signal Chain Designer
Setting Filter Specifications in Signal Chain Designer
The final Circuit tab allows you to view the filter circuit, adjust components, and view the simulated performance. The previous and next stages are shown in the upper corners and give the option to take their respective output and input impedances into account. See previous tech note for more information on impedance loading between stages.
Viewing Filter Circuit and Simulation Results in Signal Chain Designer
Now let's design a differential filter in Signal Chain Designer with help from Filter Wizard in a second tab. The Filter Wizard example below shows a 4th order Bessel Filter with passband and stopband targets included. You'll want to use the "Stages" view to collect bandwidth, order, and Q information for Signal Chain Designer.
Stages View for Filter Design in Filter Wizard Tool
Now in Signal Chain Designer, we'll drop two separate filter blocks to cover the two stages referenced in Filter Wizard. Make sure to select differential and second order options as a starting point and use the Bandwidth and Q data from Filter Wizard for each stage. Once the initial design is in place, you can adjust your component values and change your amplifier to further tune the design to meet your requirements. If you go to 4:15 in this training video, you'll see an example of going through this process.
Differential Filter Design in Signal Chain Designer using Information from Filter Wizard
Please let us know if you are having any issues building differential filters that meet your requirements on our Signal Chain Designer Engineer Zone forum.