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A method is disclosed for use in optical recording of setting the threshold level of data written in pulse width modulated (PWM) format.
English (United States)
This text was extracted from a PDF file.
This is the abbreviated version, containing approximately
72% of the total text.
Page 1 of 1
Threshold Detector for Optical Recording
A method is disclosed for use in optical recording of setting the threshold
level of data written in pulse width modulated (PWM) format.
The disclosed method relies essentially on capturing all peak and valley
levels, but only using them to update the threshold level when they correspond to
run lengths in the data which are long enough to ensure that they represent the
true high or low signal envelope values.
In an implementation using mostly analog techniques, the input analog signal
is converted to a single bit value in an analog comparator. An external phase
locked loop provides a clock signal which is used to clock a shift register which
provides the memory for the last N bit times. The outputs of the shift register are
used in the pattern detection logic to detect specific bit patterns that generate
control signals. Positive and negative peak detections are subsequently sampled
by two sample and hold circuits, and these two voltages are used as inputs to a
function generator circuit which produces the analog output voltage used as the
comparator's reference voltage. If the read signal is symmetric, then this
reference voltage would be at the mid-point of the two "rail" voltages.
In another implementation that uses a more digitally based approach, the
input signal is digitized and the peak detection functions are implemented via
digital magnitude comparators while the sample and hold functions are
implemented via latch...