CXD1958Q Просмотр технического описания (PDF) - Sony Semiconductor

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CXD1958Q

MMDS TCM/QAM Demodulator + FEC + ADC

Sony Semiconductor 

CXD1958Q

3-1. Differential Decoder

In QAM mode, this decodes the MSB of the received QAM signal according to the equations given in the

DAVIC MMDS standard. In TCM mode, the differential decoding is performed by the TCM decoder block.

3-2. TCM Decoder

The TCM decoder reduces the signal power required for robust reception in difficult channels whenever trellis

coded modulation is used at the transmitter. TCM mode is selected by an I2C bus register bit. The TCM

decoder block takes the equalized I/Q symbols as input data, and provides 7-bit (16-TCM), 11-bit (64-TCM),

and 15-bit (256-TCM) outputs for each TCM symbol. Two I/Q pairs are required for each TCM symbol. The

TCM block performs an internal synchronization sequence to ensure that the correct pair of QAM symbols is

selected. There are several I2C bus registers to allow user configuration and monitoring of the synchronization

sequence.

3-3. Symbol to Byte Mapper

The postprocessor maps differentially decoded symbols to bytes. The byte boundaries are determined by

correlating the input symbols with the expected locations of the sync bytes. The number of consecutive

successful correlations is compared against a threshold (SYNC_LADDER_LENGTH), and the symbol stream

is flagged as locked when that threshold is achieved.

3-4. De-interleaver and Reed Solomon Error Correction

DAVIC compatible forney type convolutional de-interleavering (I = 12, N = 204, M = 17) or (I = 204, N = 204, M

= 1), where M = N/I) is applied to the bytes. I = 12 is used for 16/64 QAM/TCM modes. Either I = 12 or I = 204

can be programmed for 256 QAM/TCM modes. The resulting byte stream is corrected by a standard

DAVIC/DVB (204, 188) Reed Solomon decoder (GF generation polynomial p (x) = x8 + x4 + x3 + x2 + 1) which

can correct up to 8 erroneous bytes per MPEG2 packet.

3-5. Sync Detection and Sync Loss

After R/S correction, the byte stream is checked for the occurrence of n MPEG-2 sync bytes, where n is

programmable from 2 to 7 via an I2C bus register. This sync byte detection is used to indicate transport stream

lock by activation of the TSLOCK pin. There are two methods used to indicate loss of Transport Stream Lock,

selectable by an I2C bus register. One method indicates loss of lock immediately a sync byte is lost. The other

method decrements the sync byte counter down by 1 from n, and only indicates loss of lock when the counter

reaches zero, thus providing a filtering capability to allow easier sync locking.

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