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AD6652BBC 数据表(PDF) 35 Page - Analog Devices |
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AD6652BBC 数据表(HTML) 35 Page - Analog Devices |
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35 / 76 page  AD6652 Rev. 0 | Page 35 of 76 R DC ta- lowed in the rCIC2. The resampling factor for the rCIC2 (L) is a 9-bit integer. When combined with the decimation factor M, a 12-bit number, the total rate-change can be any fraction in the form of SECOND-ORDER rCIC FILTE The rCIC2 filter is a second-order resampling cascaded integrator comb filter. The resampler is implemented using a unique technique, which does not require the use of a high- speed clock, thus simplifying the design and saving power. The resampler allows for noninteger relationships between the D CLK and the output data rate. This allows easier implemen tion of systems that are either multimode or require a master clock that is not a multiple of the data rate to be used. Interpolation up to 512 and decimation up to 4096 is al 1 2 2 ≤ = rCIC R M L R rCIC The only co than or IC2 decimates by 1 or a second-order cascaded cteristics are determined only ). rt g nstraint is that the ratio L/M must be less equal to one. This implies that the rC more. Resampling is implemented by apparently increasing the input sample rate by the factor L, using zero stuffing for the new data samples. Following the resampler is integrator comb filter. Filter chara by the fractional rate-change (L/M The filter can process signals at the full rate of the input po (65 MHz). The output rate of this stage is given by the followin equation: 2 2 2 rCIC SAMP rCIC SAMP M f L f = where: LrCIC2 and MrCIC2 are unsigned integers. LrCIC2, the interpolation rate, can be from 1 to 512. MrCIC2, the decimation, can be between 1 and 4096. The stage can be bypassed frequency response of the by setting the decimation to 1/1. The rCIC2 filter is given by the following equations: 2 2 1 ⎟ ⎞ ⎜ ⎛ − M z rCIC 1 2 2 1 2 1 ) ( 2 ⎟ ⎟ ⎟ ⎜ ⎜ ⎜ − × × = − z L L z rCIC rCIC SrCIC ⎟ ⎠ ⎜ ⎝ H 2 2 2 2 sin sin 2 1 ) ( 2 ⎟⎟ ⎟ ⎟ ⎟ ⎟ ⎠ ⎞ ⎜⎜ ⎜ ⎜ ⎜ ⎜ ⎝ ⎛ ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ π ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ × × π × × = SAMP SAMP rCIC rCIC rCIC S f f f L f M L f H rCIC Use these equations along with the following filter transfer equations to calculate the gain and pass-band droop of the rCIC2. Excessive pass-band droop can be compensated for in c rCIC2 to the least attenuation without creating an t must be programmed at 0x92 e va uld t 0x92[4:0] t date t rdware feature. ass-band d of the rCIC2 shoul the RCF stage by peaking the pass-band by the inverse of the roll-off. rCIC2 SCALE FACTOR The scale factor, SrCIC2, is a programmable unsigned 5-bit between 0 and 31, which serves as an attenuator that can reduce the gain of the rCIC2 in 6 dB increments. For the best dynami range, set S overflow condition. This can be safely accomplished using the following equation, where input_level is the largest fraction of full scale possible at the input to the AD6652 (normally 1). The SrCIC2 scale factor is always used whether or not the rCIC2 is bypassed. The SrCIC2 value must be less than 32 or the interpolation and decimation rates must be adjusted to validate this equation. The ceil function denotes the next whole integer, and the floor function denotes the current whole integer. For example, the ceil(4.2) is 5 while the floor(4.2) is 4. When SrCIC2 has been determined for all channels, i addr [9:5] of each channel o be programmed a ess register. The sam o accommo lue sho als a redundan ha The gain and p roop d be calcu- lated by the previous equations, as well as the rCIC2 filter transfer equations. Excessive pass-band droop can be compen- sated for in the RCF stage by peaking the pass-band by the inverse of the roll-off. ⎥ ⎥ ⎥ ⎥ ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎢ ⎢ ⎢ ⎢ ⎣ ⎡ ⎜⎜ ⎜ ⎜ ⎜ ⎜ ⎝ ⎛ ⎜ ⎜ ⎝ ⎛ ⎜⎜ ⎝ ⎛ × − × × ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ + = 2 log 2 2 2 2 2 2 2 2 2 rCIC rCIC rCIC rCIC rCIC rCIC rCIC rCIC L M floor L M L M floor M ceil S ⎟⎟ ⎟ ⎟ ⎟ ⎟ ⎠ ⎞ ⎟ ⎟ ⎠ ⎞ ⎟⎟ ⎠ ⎞ +1 |
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