Read and write sample and hold signal generation

#The present invention relates to optical media, and more particularly to a system and method for generating sampling control signals for a sample and hold circuit used to control access to the optical media.

#Phase changing media and write-once media, such as media used in CD writers, is written to and read from using a multi-pulse laser. A multi-pulse laser uses different laser power levels to burn data onto and read data from the media. For example, when marking a particular type of media, a write operation uses a pre-heat power level to warm up the laser, a peak power level to make an initial mark on the media, a write power level to continue making the mark, and a bias power level to cool down the laser to a non-writing level. While the commands for these power levels are digital, the resulting actual laser power level is analog.

#In general, a laser power control signal is generated in response to an internal eight-to-fourteen modulation (EFM) signal. The internal EFM signal is an encoded representation of the original data to be written to the media. EFM encoding is typically used to slow down the frequency of the original data. The internal EFM signal may be viewed as pulses of varying width (from 3T to 11T, where T is a unit timing reference for data recorded on the media), called marks, separated by spaces. As the speed of a laser device increases, the effective width of a mark (i.e. the length of time that the mark is seen by the laser) decreases.

#FIG. 1 is a schematic diagram of a conventional EFM encoding process.

#FIG. 2 is a block diagram of a conventional power sampling circuit.

#FIG. 3 is a timing diagram illustrating conventional fixed mode power sampling.

#As described below, a write strategy circuit is used to generate ROPC1 and RESMP1 sampling control signals in response to a laser power control signal EFM1, rather than directly in response to an internal EFM signal. The laser power control signal EFM1 is generated in response to the internal EFM signal. Generating the ROPC1 and RESMP1 sampling control signals in response to the EFM1 signal causes these sampling control signals to be more closely aligned with the data to be sampled.

#A user programmable delay circuit is used to generate the ROPC1 and RESMP1 sampling control signals in response to the EFM1 signal. The user programmable delay circuit allows the various edges of the ROPC1 and RESMP1 sampling control signals to be time shifted with respect to corresponding edges of the EFM1 signal. The amount of time shifting is determined by the user by programming the user programmable delay circuit to store user-selected delays. By choosing the user-selected delays in the appropriate manner, the ROPC1 and RESMP1 sampling control signals are able to sample all marks and spaces, including the marks and spaces having a minimum width. Moreover, by appropriately choosing the user selected delays, the widths of the ROPC1 and RESMP1 sampling control signals can be selected to avoid sampling transition noise. In this manner, the ROPC1 and RESMP1 sampling control signals exhibit improved on-chip delay control.

#FIG. 5 is a block diagram of a power sampling circuit 500 in accordance with an embodiment of the present invention. Power sampling circuit 500 includes write strategy circuit 510, power generator 520, sample and hold circuit 530, and laser system 540. Write strategy circuit 510 includes user programmable delay circuit 550, which in turn, includes delay lines 501-504, programmable delay control circuits 511-512, ROPC1 output control circuit 521 and RESMP1 output control circuit 522. Write strategy circuit 510 generates a plurality of laser control signals EFM1, EFM2, and EFM3, in response to an internal EFM signal (wherein the internal EFM signal has been described above in connection with FIG. 1). Laser control signals EFM1, EFM2 and EFM3 are generated in a manner known to those of ordinary skill in the art.