Lattice Semiconductor
Figure 6. Top Level Block Diagram
din_0
dout
Viterbi Decoder User’s Guide
Table 1. Core Signals
din_1
din_2
clk
reset_n
pd_start
Viterbi
Decoder
valid
pd_out
ber
ber_valid
Port
clk
reset_n
pd_start
Bits
1
1
1
I/O
Input
Input
Input
Description
System clock. The clock speed is equal to the input symbol rate.
System-wide asynchronous active-low reset signal.
Punctured data block start. This indicates the start of a new block of
punctured data. Not available while decoding non-punctured codes
din_0,
din_1,
din_2
1 or
3 to 8 (each)
Input
Data input buses.
? The buses become one-bit inputs for hard decision decoding.
? The buses are equal to the soft width for soft decision decoding.
? For punctured codes, the number of buses is one.
? For non-punctured codes, the number of buses corresponds to the
code rate: two for 1/2 rate codes, three for 1/3 rate codes.
dout
valid
pd_out
1
1
1
Output
Output
Output
Decoded data output.
This indicates the data currently presented on dout is valid.
Punctured decoder output. This indicates the data currently presented on
dout is valid. Not available while decoding non-punctured codes.
ber
ber_valid
16
1
Output
Output
Bit-error rate output
This indicates valid data is being presented at the ber output port. This
signal goes high at the end of every block of BER Period clocks.
Viterbi Decoder Con?guration Options
Con?gurable Parameters
The following core parameters give the user the capability to tailor the core to realize different con?gurations of the
Viterbi decoder.
Constraint Length: The value can be any integer from 3 to 8.
Code Rate: This is the symbol output rate of the encoder, de?ned as the number of output bits per input bit in the
encoder. For non-punctured codes, this can be equal to 1/2 or 1/3. For punctured codes, this parameter de?nes the
code rate for the mother code and is ?xed to 1/2.
Traceback Length: This is the length of the survivor sequence in the traceback through the Viterbi trellis. It can be
any value from 8 to 128.
Generator Polynomials: GP0, GP1 and GP2 are generator polynomials. GP2 is only used in non-punctured
decoders with a code rate of 3.
Implementation Methods: In the parallel implementation, the processing of data symbols is completed in one
cycle. In the hybrid implementation, it is completed in 2 hybrid index cycles.
Decoder Inputs: The decoder supports hard and soft decision decoding. For soft decision decoding, the width
(soft width) can be any integer from 3 to 8. The soft decision decoder also supports either signed or unsigned data
types. For non-punctured codes, the decoder can be con?gured either as a hard-decision or soft-decision decoder,
whereas for punctured codes, the decoder can only be a soft-decision decoder.
5
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