Microchip Technology dsPICDEM 1.1 Plus, Руководство пользователя

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dsPIC30F Demonstration Program Operation
©
2006 Microchip Technology Inc. DS70099D-page 41
TABLE 3-5: FIR FILTER SPECIFICATIONS
The filter coefficients and code were generated by the Digital Filter Design Tool.
3.5.2 Performance Metric Summary with IIR Filter
The following overall CPU performance metric is calculated on how many complete
processing cycles can be performed over a 1 second interval.
• FFT Computation:
- 26 x 256-point complex FFTs = 64.2 mS
• IIR Filter Computation:
- 26 x 9 second order elliptic section IIR filters = 101 mS
Coefficients stored in program memory
• CPU Idle:
- Waiting for ADC data = 834 mS
The 26 multiplier used in the above computations is based upon how many times in one
second 256 samples can be acquired and then processed by the IIR and FFT
algorithms.
For example:
• 32 mS for acquisition of 256 samples
• 3.89 mS for IIR filtering
• 2.47 mS for 256-point FFT
Adding these three major timing metrics results in 38.3 mS. Therefore, this
38.3 mS cycle is repeated approximately 26 times in a 1 second interval.
Total MIPS required = 1.22 MIPS out of available 7.3728 MIPS.
IIR filter specifications are listed in Table 3-6.
TABLE 3-6: IIR FILTER SPECIFICATIONS
The filter coefficients and code were generated by the Digital Filter Design Tool.
Specification Value
FIR filter type BandPass
Kaiser Window – 273 coefficients
Passband ripple 0.001 dB
Stopband ripple 100 dB
Passband cutoff frequencies 300 Hz and 3800 Hz
Stopband cutoff frequencies 100 Hz and 3990 Hz
Sampling frequency 8000 Hz
Specification Value
IIR filter type Bandpass, Elliptic, 9 Second Order Sections
Passband ripple 0.001 dB
Stopband ripple 100 dB
Passband cutoff frequencies 200 Hz and 3850 Hz
Stopband cutoff frequencies 100 Hz and 3990 Hz
Sampling frequency 8000 Hz