SYSTEM OVERVIEW

In this Application Note Motorola’s single chip demodulator and FEC for DVB-T receivers along with the usual application is described.

This section covers the overall descriptions as well as an introduction into the DVB-T standard, supporting the understanding of the special features of the OFDM system.

General Description

Before describing the important specialities of the DVB-T system itself the key features of Motorola’s single chip are outlined.

• 0.35mm CMOS process at 3.3 V.

• 160 pin QFP package

• 169 BGA package

Important capabilities of the FFT/OFDM block:

• Usable for 8 MHz, 7 MHz and 6 MHz channel bandwidth by adjusting the clock rate.

• C/N performance according to Reference [1-1] Annex A with a degradation margin of 3 dB.

• Supported DVB-T modulation schemes: QPSK, 16-QAM and 64-QAM.

• Automatic lock onto all specified guard interval lengths (1/32, 1/16, 1/8, 1/4).

• Data input: 8 Bit TTL compatible 2’s complement or offset binary.

• Channel estimation and correction using the pilot carriers.

• I2C compatible interface (M-Bus).

• Transmission Parameter Signalling (TPS) data is decoded and made available to the system controller via M-Bus.

• Processing of one block of 2048 complex samples (i.e. one 2K-OFDM symbol) in 224 ms.

• FFT input wordlength 8 bit, output accuracy 12 bit.

• Overflow on certain OFDM subcarriers due to co-channel interferes is prevented internally.

Key items of the FEC part include:

• Maximum 37 Mbit/s output rate.

• 3 Bit soft-decision input matched to the output of the OFDM block.

• Code rate 1/2 and depunctured rates of 2/3, 3/4, 5/6, and 7/8.

• Automatic or manual rate selection.

• Viterbi decoder survivor depth 96

• Signal quality output data.

• DVB compliant 12 x 17 Forney Convolutional Deinterleaver

• Reed-Solomon (204, 188, 8) decoder as specified by DVB

• DVB Descrambler for Energy Dispersal & inverted Sync Byte removal

• Bit Error Rate (BER) and uncorrectable Frame Error (BAD) monitoring

• setting of “transport_error_indicator” bit in the MPEG2 output stream (MSB of first byte immediately following the Sync Byte)