The ACE250 hardware module is part of a CD/DVD mastering system. The hardware module receives the CD/DVD encoded data from a PC via the PCI interface and generates the control signals for a laser beam recorder.
The CD/DVD encoded data is first converted into a serial bit stream after it is received. The conversion occurs on a variable clock varying from 25 to 250 MHz. In principle, the bit stream can be used directly as a control signal for a laser beam recorder. However, since the writing process is non-linear due to the properties of the movie layer, which exists on the CD or DVD, the bit stream must be corrected.
The correction involves lengthening or shortening the pulses, depending on the status of the preceding serial bit stream. The lengthening or shortening of the pulses varies from 10 ps to 10 ns. The flanks must be repositioned with an accuracy of a few picoseconds! This accuracy requires a mixed signal analogue and digital design.
The above functionality was realised in an Altera Stratix II FPGA. The variable clock (25..250 MHz) is created with the aid of direct digital synthesis (DDS). A cascade of analogue delay lines is used to lengthen and shorten the pulses. Due to the high signal frequencies, it was necessary to use ECL logic in the design. In the verification phase, the design was verified by means of a high speed signal analysis. The customer’s application software controls the module via a Windows XP driver. |
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