PS20353 Datasheet, PDF (11/27 Pages) List of Unclassifed Manufacturers – Nordig Unified DVB-T COFDM Terrestrial Demodulator

PS20353
2.4 Adjacent Channel Filtering
Adjacent channels, in particular the Nicam digital sound signal associated with analogue channels, are filtered prior
to the FFT.
2.5 Interpolation and Clock Synchronization
PS20353 uses digital timing recovery and this eliminates the need for an external VCXO. The ADC samples the signal at
a fixed rate, for example, 45.056 MHz. Conversion of the 45.056 MHz signal to the OFDM sample rate is achieved using
the time-varying interpolator. The OFDM sample rate is 64/7 MHz for 8 MHz and this is scaled by factors 6/8 and 7/8 for
6 and 7 MHz channel bandwidths. The nominal ratio of the ADC to OFDM sample rate is programmed in a PS20353
register (defaults are for 45 MHz sampling and 8 MHz OFDM). The clock recovery phase locked loop in the PS20353
compensates for inaccuracies in this ratio due to uncertainties of the frequency of the sampling clock.
2.6 Carrier Frequency Synchronization
There can be frequency offsets in the signal at the input to OFDM, partly due to tuner step size and partly due to
broadcast frequency shifts, typically 1/6 MHz. These are tracked out digitally, up to 1 MHz in 2 K and 8 K modes, without
the need for an analogue frequency control (AFC) loop.
The default frequency capture range has been set to ±286 kHz in the 2 K and 8 K mode. However, these values can be
increased, if necessary, by programming an on-chip register (see details in the design manual). It is recommended that a
larger capture range be used for channel scan in order to find channels with broadcast frequency shifts, without having to
adjust the tuner. After the OFDM module has locked (the AFC will have been previously disabled), the frequency offset
can be read from an on-chip register.
2.7 Symbol Timing Synchronization
This module computes the optimum sample position to trigger the FFT in order to eliminate or minimize inter-symbol
interference in the presence of multi-path distortion. Furthermore, this trigger point is continuously updated to dynamically
adapt to time-variations in the transmission channel.
2.8 Fast Fourier Transform
The FFT module uses the trigger information from the timing synchronization module to set the start point for an FFT. It
then uses either a 2 K or 8 K FFT to transform the data from the time domain to the frequency domain. An extremely
hardware-efficient and highly accurate algorithm has been used for this purpose.
2.9 Common Phase Error Correction
This module subtracts the common phase offset from all the carriers of the OFDM signal to minimize the effect of the
tuner phase noise on system performance.
2.10 Channel Equalization
This consists of two parts. The first part involves estimating the channel frequency response from pilot information.
Efficient algorithms have been used to track time-varying channels with a minimum of hardware.
The second part involves applying a correction to the data carriers based on the estimated frequency response of the
channel. This module also generates dynamic channel state information (CSI) for every carrier in every symbol.
2.11 Impulse Filtering
PS20353 contains several mechanisms to reduce the impact of impulse noise on system performance.
2.12 Transmission Parameter Signaling (TPS)
An OFDM frame consists of 68 symbols and a super frame is made up of four such frames. There is a set of TPS carriers
in every symbol and all these carry one bit of TPS. These bits, when combined, include information about the
transmission mode, guard ratio, constellation, hierarchy and code rate, as defined in ETS 300 744. In addition, the first
eight bits of the cell identifier are contained in even frames and the second eight bits of the cell identifier are in odd
frames. The TPS module extracts all the TPS data, and presents these to the host processor in a structured manner.
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