Philips tda1302 DATASHEETS

INTEGRATED CIRCUITS

DATA SH EET

TDA1302T

Data amplifier and laser supply
circuit for CD player and read only
optical systems

Preliminary specification
File under Integrated Circuits, IC01

Philips Semiconductors

September 1994

Philips Semiconductors Preliminary specification

Data amplifier and laser supply circuit for
CD player and read only optical systems

FEATURES

• Six input buffer amplifiers with low-pass filtering and with
virtually no offset

• HF data amplifier with a high or low gain mode

• Two built-in equalizers for single or double-speed mode

ensuring high performance in both modes

• Fully automatic laser control including stabilization and
an ON/OFF switch, plus a separate supply (V

DDL

) for

power reduction

• Adjustable laser bandwidth and laser switch-on current
slope

• Protection circuit to prevent laser damage due to supply
voltage dip

• Optimized interconnectiion between pick-up detector
and digital servo processor (TDA1301T)

• Wide supply voltage range

• Wide temperature range

• Low power consumption.

GENERAL DESCRIPTION

The TDA1302T is a data amplifier and laser supply circuit
for three-beam pick-up detectors applied in a wide range
of mechanisms for Compact Disc and read only optical
systems. The device contains 6 amplifiers which amplify
and filter the focus and radial diode signals and provides
an equalized RF signal suitable for single or double speed
mode; the mode can be switched by means of the speed
control pin. The device can accommodate astigmatic,
single foucault and double foucault detectors and can be
applied to all N-sub laser/monitor diode units even though
the circuit has been optimized for the Philips CDM12
mechanisms and the digital servo controller TDA1301T.
After a single initial adjustment the circuit will maintain
control over the laser diode current thus resulting in a
constant light output power which is independent of
ageing. The IC is mounted in a small-outline package to
enable it to be mounted close to the laser pick-up unit on
the sledge.

TDA1302T

QUICK REFERENCE DATA

SYMBOL PARAMETER CONDITIONS MIN. TYP. MAX. UNIT

V

DD

supply voltage (pin 18) 3.4 − 5.5 V

Diode current amplifiers

G

dn

I

os(d)

B 3 dB bandwidth I

amplification − 1.55 − dB
diode output offset current −−100 nA

= 1.67 µA50−−kHz

i(d)

RFE amplifier (built-in equalizer)

t

d(eq)

t

d(f)

equalization delay fi= 0.3 MHz − 320 − ns
flatness delay double-speed − 5 − ns

Laser supply

I

o(l)

output current V

=3V −−−100 mA

DDL

ORDERING INFORMATION

PACKAGE

TYPE NUMBER

NAME DESCRIPTION VERSION

TDA1302T SO24 plastic small outline package; 24 leads; body width 7.5 mm SOT137-1

September 1994 2

Philips Semiconductors Preliminary specification

Data amplifier and laser supply circuit for
CD player and read only optical systems

SCHEMATIC DIAGRAM

TDA1302T

V

V

VV

V

September 1994 3

Fig.1 Schematic diagram for CD player.

Philips Semiconductors Preliminary specification

Data amplifier and laser supply circuit for
CD player and read only optical systems

BLOCK DIAGRAM

TDA1302T

September 1994 4

Fig.2 Block diagram.

Philips Semiconductors Preliminary specification

Data amplifier and laser supply circuit for
CD player and read only optical systems

PINNING

SYMBOL PIN DESCRIPTION

O4 1 output of diode current amplifier 4
O6 2 output of diode current amplifier 6
O3 3 output of diode current amplifier 3
O1 4 output of diode current amplifier 1
O5 5 output of diode current amplifier 5
O2 6 output of diode current amplifier 2
LDON 7 control pin for switching the laser

ON and OFF

V

DDL

RFE 9 equalized output voltage of sum

RF 10 unequalized output
HG 11 control pin for gain switch
LS 12 control pin for speed switch
CL 13 external capacitor
ADJ 14 reference input normally

GND 15 0 V supply; substrate connection

LO 16 current output to the laser diode
MI 17 laser monitor diode input
V

DD

I2 19 photo detector input 2 (central)
I5 20 photo detector input 5 (satellite)
I1 21 photo detector input 1 (central)
I3 22 photo detector input 3 (central)
I6 23 photo detector input 6 (satellite)
I4 24 photo detector input 4 (central)

8 laser supply voltage

signal of amplifiers 1 to 4

connected to ground via a resistor

(ground)

18 amplifier supply voltage

TDA1302T

Fig.3 Pin configuration.

September 1994 5

Philips Semiconductors Preliminary specification

Data amplifier and laser supply circuit for
CD player and read only optical systems

FUNCTIONAL DESCRIPTION

The TDA1302T can be divided into two main sections, the
laser control circuit and the photo diode signal filter and
amplification section.

Laser control circuit

The main function of the laser control circuit is to control
the laser diode current in order to achieve a constant light
output power which is based on the current of the monitor
diode which is continuously monitored. The circuit is built
up into three parts.

The first part is the input stage which compares the
monitor diode current with a current which is 10 times the
value of the adjustable current. The adjustable current is
derived from a bandgap reference source, to be
temperature independent, and can be further adjusted by
the external resistor R
parameters of the laser/monitor diode unit to be used. The
difference is fed to the second part.

The second part is the integrator stage which makes use
of an external capacitor CL. This capacitor has two
different functions.

During switch-on of the laser current, it provides a current
slope of typically: dILO/dt ≅ 10−6/CL (A/s).

After switch-on it ensures that the bandwidth conforms to
the typical formula: fB≅ K × A

where A

represents the AC gain of an extra loop

ext

amplifier, if applied, and K = dI
determined by the laser/monitor unit.

I

is the average current (pin 17) at typical light

MON

emission power of the laser diode.

in order to adapt the circuit to the

ADJ

× 90−9/(CL × I

ext

monitor

/dI

laser

MON

which is

) (Hz).

TDA1302T

The third part is the power output stage, its input being the
integrator output signal. This stage has a separate supply
voltage (V
power consumption by supplying this pin with the minimum
voltage necessary.

It also has a laser diode protection circuit which is enabled
prior to the output drive transistor becoming saturated due
to a large voltage dip on V
lower current from the laser diode, which is normally
followed immediately by an increment of the voltage from
the external capacitor CL, which could cause damage to
the laser diode at the end of the voltage dip. The protection
circuit prevents an increment of the capacitor voltage and
thus offers full protection to the laser diode under these
circumstances.

Photo diode signal filter and amplification section

This section has 6 identical current amplifiers. Amplifiers 1
to 4 are designed to amplify the focus photo diode signals.
Each amplifier has two outputs, an LF output and an
internal RF output. Amplifiers 5 and 6 are used for the
radial photo diode currents and have only an LF output. All
6 output signals are low-pass filtered with a corner
frequency at 65 kHz. The internal RF output signals are
summed together and converted into a voltage by means
of a selectable transresistance of 120 kΩ or 240 kΩ. This
signal is available directly at pin 10, however, there is also
an unfiltered signal available at pin 9. The equalization
filter used has 2 different filter curves, one for single-speed
mode and one for double-speed mode.

) thereby offering the possibility of reduced

DDL

. Saturation will result in a

DDL

Table 1 Operational modes.

SWITCH PIN

HG 1 1 0 X X X X

Control pin

LS 1 X X 1 0 X X
LDON 1 X X X X 1 0

Note

1. Where X = don’t care.

September 1994 6

IF NOT

CONNECTED

DEFAULT

(1)

MODE

GAIN SPEED LASER

HIGH LOW SINGLE DOUBLE ON OFF