Direct form and parallel form are two different structures used to implement digital filters in a digital controller. Both structures have their advantages and disadvantages and are suitable for different applications.
The main differences between direct form and parallel form are as follows:
Processing order: In direct form, the input signal is processed sequentially through a series of adders and multipliers. In parallel form, the input signal is split into multiple sub-signals, which are processed independently in parallel by subfilters.
Efficiency: Direct form is generally less efficient than parallel form, as it requires more processing time to generate the filtered output signal. Parallel form, on the other hand, can process the sub-signals in parallel, resulting in faster processing times.
Frequency response: Direct form provides a wider range of frequency response control as the coefficients are applied directly to the input signal. Parallel form, however, can provide better control over the frequency response in specific frequency ranges by processing different sub-signals with different subfilters.
Complexity: Direct form is a simpler structure than parallel form, as it requires fewer adders and multipliers to implement. Parallel form, however, is a more complex structure that requires additional circuitry to split the input signal into sub-signals and to combine the output signals of the subfilters.
In summary, direct form is generally simpler to implement but may have limited frequency response control, while parallel form is more complex but can provide better frequency response control and faster processing times. The choice between the two structures depends on the specific application and the performance requirements of the digital controller.
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