Fig. 21 - Analog View with AMM
Focus Error / Tracking Error
The Focus and Tracking error test can be performed on a blank recordable disc. When a blank disc is loaded, the Blank
Test checkbox will be enabled, otherwise it is disabled. No other tests can be performed on a blank disc.
Components of the HF Signal
The HF (High Frequency) signal coming from the pickup represents the light intensity of the beam reflected back from
the disc surface. A higher voltage represents greater light intensity, and a lower voltage represents less light. The
signal is rapidly changing between light and dark as the beam passes over the pits. When the beam is over a pit, the
light intensity is reduced. When the beam is between pits (over “land”), the light intensity is higher. Data is encoded in
the transitions between pits and lands.
CD HF Signal
The eight-to-fourteen (EFM) modulation scheme used produces just nine different possible lengths of pits and lands.
Therefore, the resulting HF consists of square waves of nine different durations. The signal appears sinusoidal on the
‘scope because of the limited frequency response of the optics. The “eye pattern” displayed on the oscilloscope is a
superposition of many sweeps, each consisting of up to nine different lengths. Each of the nine pit/land lengths are
exact multiples of one fundamental length, called 1T. The nine possible lengths of pits and lands are 3T, 4T, 5T, 6T,
7T, 8T, 9T, 10T, and 11T. The waveforms generated by these pits & lands are called I
3
, I
4
, I
5
, I
6
, I
7
, I
8
, I
9
, I
10
, and I
11
respectively. I
3
represents the shortest pit / land, and I
11
represents the longest pit or land. Generally, we only need to
look and the longest and shortest pits to get a good picture of pit geometry.
DVX
Instruction
Manual
33
