Barrel shifter

Inactive Publication Date: 2006-11-09
STMICROELECTRONICS SRL
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0014] To achieve these objects and others, the present invention provides a barrel shifter for which the surface overhead is reduced.
[0015] Another object of the present invention is to provide a barrel shifter which can be realized with a number of multiplexers equal to or very slightly greater than the number of multiplexers of a barrel shifter with a logarithmic structure.

Problems solved by technology

One difficulty during application of a barrel shifter with logarithmic structure is due to the large irregularity in the lengths of the paths 19 and the large number of junctions between paths 19 required by the arrangement of multiplexers.
This leads to a large increase of the surface overhead when the number of symbols and / or the number of bits per symbol becomes large.
This results in barrel shifters which are very bulky.
Another drawback comes from the fact that an increase in the surface area of a barrel shifter brings about an increase in the length of at least some of the paths taken by symbols.
A problem is that transmission time of a symbol along a path depends on the path length.
If the transmission time of symbols (or at least of some of them) is too large, it may not be possible to perform a shift operation in one cycle of the clock which controls the operation of the barrel shifter.

Method used

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Examples

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Embodiment Construction

[0047] For reasons of clarity, the same elements have been labeled with the same reference characters in the different figures.

[0048] The present invention provides a barrel shifter receiving N symbols and comprising at least two successive stages, each comprising a determined number, possibly different per stage, of elementary barrel shifters, the elementary barrel shifters of the first stage being linked to the elementary barrel shifters of the second stage. Each elementary barrel shifter receives only one part of N symbols on which it performs a shift operation. The present invention allows a limitation of the variation in lengths and the number of junctions of the paths of the barrel shifter, and therefore limitation of the surface area overhead of the barrel shifter.

[0049]FIG. 4 shows the general structure of an example of a barrel shifter 20. The device 20 receives N symbols, each symbol being comprised of nbit_data bits, and outputs N symbols on which a circular shift (barr...

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Abstract

A barrel shifter receiving N symbols, arranged n2 distinct groups of n1 symbols, applying a circular shift to the N symbols. The barrel shifter comprises n2 first barrel shifters, each applying a first circular shift to one of the groups of n1 symbols; a rearrangement module receiving the N symbols provided by the first barrel shifters and providing N symbols arranged, in a determined manner, in n1 distinct groups of n2 symbols; n1 second barrel shifters, each applying a second circular shift to one of the distinct groups of n2 symbols; a control module providing, to each first barrel shifter, an identical signal bs_ctrl1 representing the first shift, and providing, to each second barrel shifter, an identical signal bs_ctrl2 representing the second shift; and a switching module switching at least two of the symbols of the N symbols.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a barrel shifter for symbols. [0003] 2. Discussion of the Related Art [0004] An example of an application of a barrel shifter device relates to decoding symbols transmitted according to the DVB-S2 standard using an error correction code of the type LDPC (Low Density Parity Check). [0005]FIG. 1 schematically shows a barrel shifter 10 (BS) receiving N symbols 12 in parallel arranged in a certain order, each symbol corresponding to a coded digital message of a determined number of bits nbit_data. The device 10 outputs in parallel N symbols 14, which correspond to N received symbols 12, on which a circular shift has been applied, to the left or to the right, by a number of positions which can be chosen to be between 0 and N-1. The barrel shifter 10 receives a control signal bs_ctrl from which the number of positions that the received symbols 12 are to be shifted can be determined. [0006]...

Claims

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Application Information

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IPC IPC(8): G11C19/00
CPCG11C19/287
InventorPAUMIER, LAURENTURARD, PASCAL
OwnerSTMICROELECTRONICS SRL