P32P4910 datasheet(13/64 Pages) PHILIPS

13 / 64 page

1996 May 29

Philips Semiconductors

Product speciﬁcation

PRML Read Channel with PR4,

8/9 ENDEC, 4-Burst Servo

P32P4910A

With a zero at the origin, the filter provides a time-differentiated filter output. This is used in time qualification of the peak

detection. To ease the timing requirement in peak detection of a signal slightly above the qualification threshold, the

time-differentiated output is purposely delayed by 1.2 ns relative to the normal low pass output.

The normal low pass output feeds the data qualifier (DP/DN), and the differentiated output feeds the clock comparator

(CP/CN).

Five definitions are introduced for the programmable filter control discussion (Figure 6):

Cutoff Frequency: The cutoff frequency is the -3 dB low pass bandwidth with no boost and group delay equalization, i.e.

α=0 and β=0.

Actual Boost: The amount of peaking in magnitude response at the cutoff frequency due to

α≠0 and/or β≠0.

Alpha Boost: The amount of peaking in magnitude response at the cutoff frequency due to

α≠0 and without group delay

equalization. In general, the actual boost with group delay equalization is higher than the alpha boost. However, with

>3 dB alpha boost, the difference is minimal.

Group Delay

∆%: The group delay ∆% is the percentage change in absolute group delay at DC with respect to that

without equalization applied (

β=0).

Group Delay Variation: The group delay variation is the change in group delay from DC to the cutoff frequency. This

can be expressed as a percentage defined as: (change in group delay

÷ absolute group delay with β=0) * 100%. An

alternative is to express the group delay variation in nanoseconds. Because the absolute group delay variation in

nanoseconds is scaled by the programmed cutoff frequency, the percentage expression is used in this specification.

SM00010

Ts2–bs+1.31703

s2+1.68495s+1.31703

2.95139

s2+1.54203s+2.95139

5.37034

s2+1.14558s+5.37034

0.86133

s+0.86133

Normal

Differential

Figure 5: Programmable Filter Normalized Transfer Function

P32P4910 Datasheet(PDF) 13 Page - NXP Semiconductors