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HSP43168 Datasheet(PDF) 7 Page - Intersil Corporation |
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HSP43168 Datasheet(HTML) 7 Page - Intersil Corporation |
7 / 25 page 7 Bank. As shown in Figure 2, either Configuration Control Register can be written to during reset. The 4 LSBs of the control word loaded at address 000H are used to select the decimation factor. The Decimation Factor is programmed to one less than the number of delays between filter taps For example, if the 4 LSBs are programmed with a value of 0010, the Forward and Reverse Shifting Decimation Registers are each configured with a delay of 3. Bit 4 is used to select whether the FIR cells operate as two independent filters or one extended length filter. Dual filter mode assumes Filter A and Filter B are separate independent filters. In the single filter mode, the data is routed through the forward paths of Filters A and B before entering the reverse paths of Filters A and B (see Figure 1). Coefficient symmetry is selected by bit 5. Bits 6 and 7 are programmed to configure the FIR cells for odd or even filter lengths (number of taps). Bit 8 selects the FIR B input source when the FIR cells are configured for independent operation. Bit 9 must be programmed to 0. NOTE: When the filter is programmed for even-taps, the TXFR signal is delayed by only three CLKS (see Figure 1). For odd-taps, the TXFR signal is delayed by four CLKS. The 4 LSBs of the control word loaded at address 001H are used to configure the format of the FIR cell's data and coefficients. Bit 4 is programmed to enable or disable the reversal of data sample order prior to entering the Reverse Path Decimation Registers. Data reversal is required for symmetric filter coefficient sets of both even or odd numbers of filter taps. Asymmetric filters and some decimated symmetric filters require the data reversal to be off. Bits 5-9 are used to support programmable rounding on the output. FIR Filter Cells Each FIR filter cell is based on an array of four 11x10-bit two's complement multipliers. One input of the multipliers comes from the ALU’s which combine data shifting through the Forward and Reverse Decimation Registers. The second multiplier input comes from the user programmable coefficient bank. The multiplier outputs are fed to an accumulator whose result is passed to the output section where it is multiplexed or added with the result from the other FIR cell. Decimation Registers The Forward and Reverse Decimation Shift Registers can be configured for decimation factors from 1 to 16 (see Table 1, bits 0-3). NOTE: Setting the decimation factor only affects the Delay Registers between filter taps, not the filter control multiplexers. Example 4 and Example 5 in the Applications Section discuss how to configure the part for actual decimation applications. The Reverse Shifting Registers with the data reversal logic are used to take advantage of symmetry in linear phase filters by aligning data at the ALUs for pre-addition prior to multiplication by the common coefficient. When the FIR cells are configured in single filter mode, the Decimation Registers in FIR cell A and FIR cell B are cascaded. This extended filter tap delay path allows computation of a filter which is twice the size of that capable using a single cell. The Decimation Registers also provide data storage for polyphase or 2-D filtering applications (See Applications Examples Section). The Data Feedback Circuitry in each FIR cell is responsible for transferring data from the Forward to the Reverse Shifting Decimation Registers. This circuitry feeds blocks of samples into the reverse shifting decimation path in either reversed or non-reversed sample order. The MUX/DEMUX structure at the input to the Feedback Circuitry routes data to the LIFOs or the delay stage depending on the selected TABLE 1. CONFIGURATION/CONTROL WORD 0 BIT DEFINITIONS CONTROL ADDRESS 000H BITS FUNCTION DESCRIPTION 3-0 Decimation Factor (N) R = N + 1 0000 = No Decimation. 1111 = Decimation by 16. 4 Mode Select 0 = Single Filter Mode. 1 = Dual Filter Mode. (also 20-Bit Coefficient Filter) 5 Odd/Even Filter Coefficient Symmetry 0 = Even Symmetric Coefficients. 1 = Odd Symmetric Coefficients. 6 FIR A Odd/Even Number of Taps 0 = Odd Number of Taps in Filter. 1 = Even Number of Taps in Filter. 7 FIR B Odd/Even Number of Taps (Defined Same as FIR A Above). 8 FIR B Input Source 0 = Input from INA0-9. 1 = Input from INB0-9. 9 Not Used Set to 0 for Proper Operation. NOTE: Address locations 002H to 011H are reserved, and writing to these locations will have unpredictable effects on part configuration. TABLE 2. CONFIGURATION/CONTROL WORD 1 BIT DEFINITIONS CONTROL ADDRESS 001H BITS FUNCTION DESCRIPTION 0 FIR A Input Format 0 = Unsigned. 1 = Two's Complement. 1 FIR A Coefficient Format (Defined same as FIR A input). 2 FIR B Input Format (Defined same as FIR A input). 3 FIR B Coefficient (Defined same as FIR A input). 4 Data Reversal Enable 0 = Enabled. 1 = Disabled. 8-5 Round Position 0000 = 2-10. 1011 = 21. (See Figure 4) 9 Round Enable 0 = Enabled. 1 = Disabled. NOTE: Address locations 002H to 011H are reserved, and writing to these locations will have unpredictable effects on part configuration. DF CLK delays between taps () 1 – = (EQ. 1) HSP43168 |
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