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AD6652BBC 数据表(PDF) 37 Page - Analog Devices |
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AD6652BBC 数据表(HTML) 37 Page - Analog Devices |
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37 / 76 page  AD6652 Rev. 0 | Page 37 of 76 er ion, FIFTH-ORDER CIC FILTER The fourth signal processing stage, CIC5, implements a sharp fixed-coefficient, decimating filter than rCIC2. The input rate to this filter is fSAMP2. The maximum input rate is given by the following equation. NCH equals two for diversity channel real input mode; otherwise, NCH equals one. To satisfy this equat increase MrCIC2 or reduce NCH. CH CLK SAMP N f f ≤ 2 The decimation ratio, MCIC5, can be programmed from 2 to 32 (all integer values). The frequency response of the filter is given by the following equations. Use these equations to calculate the gain and pass-band droop of CIC5. Both parameters can be compensated for in the RCF stage. 5 1 5 1 1 2 1 ) ( 5 5 ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ − − × = − − + z z z H CIC CIC M S 5 2 2 5 5 sin sin 2 5 ⎜ ⎜ CIC 1 ) ( ⎜ ⎜ × = f H ⎟ ⎟ ⎟ ⎟ ⎟ ⎞ ⎜ ⎛ ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ π ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ × π + SAMP CIC S f f f f M tion without creating an ⎠ ⎝ SAMP The scale factor, SCIC5, is a programmable unsigned integer between 0 and 20. It serves to control the attenuation of the data into the CIC5 stage in 6 dB increments. For the best dynamic range, set SCIC5 to the least attenua overflow condition. This can be safely accomplished using the following equation, where OLrCIC2 is the largest fraction of full scale possible at the input to this filter stage. This value is output from the rCIC2 stage, then pipelined into the CIC5. ( ) ( ) 5 log 2 5 5 2 5 − × = rCIC CIC CIC OL M ceil S () 2 5 5 5 5 5 2 rCIC S CIC CIC OL M OL CIC × = + The output rate of this stage is given by the following equation: 5 2 5 CIC SAMP SAMP M f f = CIC5 REJECTION Table 15 lists the amount of bandwidth in percentage of the input rate that can be protected with various decimation rates and alias rejection specifications. The maximum input rate into the CIC5 is 65 MHz when the rCIC2 decimates by 1. As in the previous rCIC2 table (Table 14), these are the single-sideband bandwidth characteristics of the CIC5. he f an upper bound on decimation, MCIC5. Table 15. SSB CIC5 Alias Rejection Table (fSAMP2 = 1) MCIC5 −50 dB −60 dB −70 dB −80 dB −90 dB −100 dB The CIC5 stage can protect a much wider band to any given rejection than rCIC2. Given the desired filter characteristics, Table 15 can help in t calculation o 2 10.277 8.078 6.393 5.066 4.008 3.183 3 7.924 6.367 5.11 4.107 3.297 2.642 4 6.213 5.022 4.057 3.271 2.636 2.121 5 5.068 4.107 3.326 2.687 2.17 1.748 6 4.267 3.463 2.808 2.27 1.836 1.48 7 3.68 2.989 2.425 1.962 1.588 1.281 8 3.233 2.627 2.133 1.726 1.397 1.128 9 2.881 2.342 1.902 1.54 1.247 1.007 10 2.598 2.113 1.716 1.39 1.125 0.909 11 2.365 1.924 1.563 1.266 1.025 0.828 12 2.17 1.765 1.435 1.162 0.941 0.76 13 2.005 1.631 1.326 1.074 0.87 0.703 14 1.863 1.516 1.232 0.998 0.809 0.653 15 1.74 1.416 1.151 0.932 0.755 0.61 16 1.632 1.328 1.079 0.874 0.708 0.572 17 1.536 1.25 1.016 0.823 0.667 0.539 18 1.451 1.181 0.96 0.778 0.63 0.509 19 1. 483 375 1.119 0.91 0.737 0.597 0. 20 1.307 1.064 0.865 0.701 0.568 0.459 21 1.245 1.013 0.824 0.667 0.541 0.437 22 1.188 0.967 0.786 0.637 0.516 0.417 23 1.137 0.925 0.752 0.61 0.494 0.399 24 1.09 0.887 0.721 0.584 0.474 0.383 25 1.046 0.852 0.692 0.561 0.455 0.367 26 1.006 0.819 0.666 0. 4 3 5 0.437 0.35 27 0.969 0.789 0.641 0.52 0.421 0.34 28 0.934 0.761 0.618 0.501 0.406 0.328 29 0.902 0.734 0.597 0.484 0.392 0.317 30 0.872 0.71 0.577 0.468 0.379 0.306 31 0.844 0.687 0.559 0.453 0.367 0.297 32 0.818 0.666 0.541 0.439 0.355 0.287 –150 –130 –110 –90 –70 –50 –30 –10 –2 –1 0 1 2 +10 MULTIPLES OF CIC5 OUTPUT RATE Figure 48. Double Side-Band Graph Showing CIC5 Filter Response and Alias Rejection of −100 dB |
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