MC92307

• Processing of one block of 2048 complex samples (i.e. one 2K-OFDM symbol) in 224 s.
• Designed for direct interfacing with Motorola's OFDM demodulator MC92308.
• Input wordlength 8 bit, output accuracy selectable between 10 and 12 bit.
• Overflow on certain OFDM subcarriers due to co-channel interferes is handled internally.
• Readout of output samples can be shifted by half the blocklength to start at the middle of the output block.
• Either multiplexed or non-multiplexed input and output format (the multiplexed mode allows direct interfacing with Motorola's OFDM Demodulator MC92308).
• Internal Bit reversal can be disabled to allow the construction of FFT modules for blocklengths > 2K by using several devices in parallel.
• Low clock rate inputs and outputs.
• 0.5m CMOS process at 3.3 V.
• 5 V tolerant inputs and outputs.

As already mentioned the FFT device is especially suited to be combined with Motorola's OFDM device MC92308 to form the complete digital part of a frontend for a 2K DVB-T receiver. Refer to Figure 6 for the functional blocks of a terrestrial DVB receiver. Further details of the blocks are given in reference [2]. One of the key signals for the successful reception of an OFDM signal is the correct timing synchronization, that means that the synchronization circuitry chooses the correct starting point to trigger the FFT operation. Therefore the OFDM demodulator MC92308 provides the FFTSTART signal to the FFT device. If 2048 complex time domain samples have been read into the input buffer the FFT operation starts. Its result is flagged with the SYMSYNC line and the calculated frequency domain samples are output to the OFDM device that continues with the demodulation process.

The MC92307 is a pipelined Fast Fourier Transformation (FFT) processor with a blocklength of 2048 complex samples. It is especially designed for use in digital terrestrial Set-Top boxes according to the DVB-T standard for 2K tansmission. One block of 2048 complex samples can be processed in 224 s