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HSP43124SC-45Z Datasheet(PDF) 10 Page - Intersil Corporation |
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HSP43124SC-45Z Datasheet(HTML) 10 Page - Intersil Corporation |
10 / 18 page 10 The coefficient set for each of the halfband filters is given in Table 4. These values are the 32-bit, two’s complement, integer representation of the filter coefficients. Scaling these values by 2-31 yields the fractional two’s complement coefficients used to achieve unity gain in the Filter Processor. If a specific frequency response is desired, a programmable FIR filter may be activated. The filter compute engine takes advantage of symmetry in FIR coefficients is by summing data samples sharing a common coefficient prior to multiplication. In this manner, two filter taps are calculated per multiply accumulate cycle. If an asymmetric filter is specified, only one tap per multiply accumulate cycle is calculated. The processing rate of the Filter Compute Engine is proportional to FCLK. As a result, the frequency of FCLK must exceed a minimum value to insure that a filter calculation is complete before the result is required for output. In configurations which do not use decimation, one input sample period is available for filter calculation before an output is required. For configurations which employ decimation, up to 256 input sample periods may be available for filter calculation. The following equation specifies the minimum FCLK rate required for configurations which use the programmable filter as an FIR filter. In this equation FS is the input sample rate (SCLK/# Bits in SER word), TAPS is the number of taps in the FIR filter (0 to 256), DECFIR is the decimation rate of the programmable FIR (1 to 8), HBCLKS is a compute clock factor based on the number of halfband filters in the configuration (see Table 5), and DECHB is the aggregate decimation rate for the cascade of halfband filters (see Table 5). For example, if the input sample rate is 800kHz, a 128 tap FIR filter with no decimation is selected, and a cascade of 2 halfband filters is used, calculate the minimum FCLK rate as follows: Thus, the Min FCLK is 19.6MHz. NOTE: For configurations in which the halfband filters are used, the FCLK rate must exceed 14FS. The longest length FIR filter realizable for a particular configuration is determined by solving the above equation for TAPS. The resulting expression is given below. The maximum throughput sample rate may be specified by solving the above equation for FS. The resulting equation is NOTE: For configurations using filters with asymmetric coeffi- cients, the term TAPS in the above equations should be multi- plied by two in order to determine the correct FCLK. The Filter Compute Engine is synchronized with an incoming data stream by asserting the FSYNC input. When this input is sampled low by the rising edge of FCLK, the Compute Engine is reset, and the data word following the next assertion of SYNCIN is recognized as the first data sample input to the filter structure. Min FCLK FS DECHB -------------------- TAPS/(2*DECFIR) HBCLKS 1 ++ () or at least14FS when Halfbands are used ⎩ ⎪ ⎨ ⎪ ⎧ = (EQ. 2) (EQ. 3) Min FCLK 800kHz 4 --------------------- ⎝⎠ ⎛⎞ 128 2 1 ---------- ⎝⎠ ⎛⎞ 33 1 ++ ⎝⎠ ⎛⎞ 200kHz () 64 33 1 ++ [] 19.6MHz = or at least 14 (800kHz) 11.2MHz = ⎩ ⎪ ⎪ ⎨ ⎪ ⎪ ⎧ = Max TAPS = 2DECFIR((FCLK/FS)DECHB - HBCLKS - 1) (EQ. 4) Max FS = FCLK*DECHB /(TAPS/(2*DECFIR) + HBCLKS + 1). (EQ. 5) TABLE 3. FREQUENCY RESPONSE OF HALFBAND FILTERS NORMALIZED FREQUENCY HALFBAND #1 HALFBAND #2 HALFBAND #3 HALFBAND #4 HALFBAND #5 0.000000 -0.000000 0.000000 0.000000 -0.000000 -0.000000 0.007812 0.000000 -0.000000 -0.000000 -0.000000 -0.000000 0.015625 -0.000113 -0.000000 -0.000000 -0.000000 -0.000000 0.023438 -0.000677 -0.000006 -0.000000 -0.000000 -0.000000 0.031250 -0.002243 -0.000052 -0.000000 -0.000000 -0.000000 0.039062 -0.005569 -0.000227 -0.000000 -0.000000 0.000000 0.046875 -0.011596 -0.000719 -0.000001 0.000000 -0.000000 0.054688 -0.021433 -0.001859 -0.000009 -0.000000 -0.000000 0.062500 -0.036333 -0.004165 -0.000041 -0.000000 -0.000000 0.070312 -0.057670 -0.008391 -0.000149 -0.000001 -0.000000 0.078125 -0.086916 -0.015557 -0.000448 -0.000012 -0.000000 0.085938 -0.125619 -0.026983 -0.001175 -0.000066 -0.000000 0.093750 -0.175382 -0.044301 -0.002767 -0.000258 -0.000000 HSP43124 |
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