TZA1020HP/A View Datasheet(PDF) - Philips Electronics

Part Name

Description

Manufacturer

TZA1020HP/A

Pre-amplifiers for CD-RW systems

Philips Electronics 

Philips Semiconductors

Pre-amplifiers for CD-RW systems

Product specification

TZA1020; TZA1020A

7 FUNCTIONAL DESCRIPTION

All functions are designed in such a way that a read speed

up to twelve times nominal speed is possible

(N = 1, 2, 4, 8 or 12). Recording speed up to four is

possible (N = 1, 2 or 4). The maximum recording speed

must be determined.

7.1 Data amplifier

The central diodes currents (C1 to C4) are fed to a high

bandwidth current amplifier. The gain of the current

amplifier can be switched by means of the I2C-bus

microcontroller interface to compensate for differences in

CD-R and CD-RW disc reflection. Data signals up to

twelve times nominal data speed can be read.

7.2 Normalizer

The currents from the central diodes (C1 to C4), the

current from the satellite diodes (SA1, SA2, SB1 and SB2)

and the laser set-point current (CAGAIN) are (optionally

sampled) fed to the first low-pass filters with a bandwidth

of 60 kHz. The normalizing circuit generates error signals

for servo control that are independent of the diode current

level. The gain of the error signals is controlled by the

I2C-bus microcontroller interface. A dropout concealment

becomes active if the input current level is below a certain

threshold value. This threshold value is also controlled by

the I2C-bus.

7.3 Wobble pre-processor

The wobble signal of the pre-groove is detected by means

of the PPN signal. The currents from inputs C1 to C4 are

filtered and processed to provide optimal signal-to-noise

ratio. The bandwidth of the filter may be adapted to the

disc speed via the I2C-bus. The bandwidth of a noise

reduction loop is controlled by an external capacitor, the

I2C-bus interface controls the total operation of the

processor.

7.4 Beta detector

The beta detector generates signals necessary for the

symmetry detection of the HF signal. By measuring peak

values (A1 and A2) and average value of the signal

(CALF), an optimum laser writing power can be

determined. The gain of the measured values is controlled

by the I2C-bus. The time constant of the peak detectors

and bandwidth of the low-pass filtered aperture signal can

also be adapted to the disc speed by the I2C-bus.

7.5 Alpha detector

The alpha detector determines a parameter called ‘alpha’

during disc writing. Alpha must be kept constant to allow

recording over a fingerprint or black dot. The definition of

alpha is different for CD-R and CD-RW; for CD-R the light

absorption of the disc is measured, for CD-RW alpha is

determined by actual laser power and disc reflection. The

gain of the measured signals and the CD-R and CD-RW

selection is performed by the I2C-bus.

7.6 Fast track count

The fast track count circuit generates a Radial Error (RE)

signal for fast track counting. A gain switch compensates

for difference in CD-R and CD-RW disc reflection.

7.7 Spot position measurement

To allow alignment of photo diodes via the TZA1020, a

number of linear combinations of input currents can be

realized (MEAS1 and MEAS2). Selection of the actual

combination is performed by the I2C-bus.

2000 Oct 30

7

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