A Programmable DSP-based PLL for Digital TV Receivers
A programmable DSP-based phase locked loop (PLL) for DTV receiver carrier and timing recovery loops was developed. Instead of processing the incoming data at sampling rate, A block of data with N samples are processed at a time. The block sizes can be varied based on the signal condition, and the state of the phase locked loop. This results in more flexible front-end design, which is an important factor for multi-mode receivers. Three different implementations of the block-based approach are described, together with simulation results and DSP implementation.
Background & Objective: The era of digital television broadcasting in the U.S. began with the introduction of terrestrial services in November 1998. Cable and satellite digital TV broadcasting services will soon become available as well. Because of the high similarity in source coding used throughout all three transmission media (terrestrial, cable and satellite), where MPEG-2 is the common standard for video and audio coding, it is possible to share signal processing functional blocks across the three media. In current generation digital TV receivers, due to the high data throughput, (e.g. the symbol rates: 10.76MHz for 8VSB, 5.38MHz for 256QAM, and up to 45MHz for QPSK,) the conventional approach of implementation is hardware. The hardware approach can offer a high computation speed but is very difficult to change for future upgrade, and the size of the chip is usually quite large, typically accompanied with a long development cycle. In this paper, we present a new solution to the multi-mode demodulator front-end that is based on programmable DSP, and re-configurable logic.
Technical Discussion: The function of phase detector block is to extract phase error from equalizer output xn. An integrator for average is introduced prior to the loop filter. This average block takes a block of N data from the phase detector and put the average to the loop filter every block, Ts is the sampling interval. Since the number of operation is reduced for the loop filter and NCO, both parts can be implemented in DSP software. The block size N can vary at the different stage, such as the acquisition and tracking state.
Contact: Huifang Sun
Technology Area: Advanced Digital Television
Modification Date: March 13, 2003
