參數(shù)資料
型號: L64777
廠商: LSI CORP
元件分類: 消費(fèi)家電
英文描述: Digital Video Broadcasting(DVB)-Compliant,quadrature amplitude modulation (QAM)Modulator(數(shù)字視頻廣播系統(tǒng)適配的積分調(diào)幅調(diào)制器)
中文描述: SPECIALTY CONSUMER CIRCUIT, PQFP120
封裝: 32 MM, PLASTIC, QFP-120
文件頁數(shù): 41/124頁
文件大?。?/td> 988K
代理商: L64777
Square Root Nyquist Filter
2-27
Differential encoding has an infinite error propagation. You can switch it
off independently from the mapping function (see bit 3 of Register 6, on
page 4-8).
2.11 Square Root Nyquist Filter
This pulse-shaper module implements a programmable square-root
raised cosine filtering function with a default 15% roll-off factor. The
precision of the internal Nyquist filter computations, and the width of the
output data bus, are sufficient for QAM modulations up to 256. The filter
operates at four times the oversampling rate. Figure 2.19 illustrates the
structure of the pulse shaper.
Figure 2.19 Pulse Shaper Structure
Note that the 20 bits per channel is a result of the length of each
coefficient register (2
11
) plus the length of INQ (2
4
) plus the number of
stages (30 = 2
5
). The total number of coefficients is 124 (there is one
coefficient set for each of the four phases multiplied by the MAC
structure, which contains 31 multipliers).
Each of the two I and Q branches has one filter, realized as polyphase
structures. Each filter consists of four filter branches, which compute
1-phase filter results at the symbol rate. Thus, the L64777 Nyquist filter
module generates the desired pulse shape by combining the outputs of
four identical filter branches for I and Q.
From Coefficient Register (Register 0)
to Shifter
Numbers represent coefficient
word width of MAC structures
IS[19:0],
11 bit
offset
QS[19:0]
C0 C1 C2 C3 C4 C5 C6
C7 C8 C9
C23 C24 C25C26 C27 C28 C29 C30
11
11
11
11
11
11
11
11
11
11
11
11
11
11
11
11
11
11
The big adder
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