Philips tza1025 DATASHEETS

INTEGRATED CIRCUITS

DATA SH EET

TZA1025

Data amplifier and laser supply circuit for CD audio and video optical systems (ADALASLC)

Product speciﬁcation File under Integrated Circuits, IC01

1998 Oct 30

Philips Semiconductors Product speciﬁcation

Data ampliﬁer and laser supply circuit for CD audio and video optical systems (ADALASLC)

FEATURES

• Supports a wide range of voltage output mechanisms

• RF amplifier designed for audio and video applications with 1 × data rate

• Programmable RF gain for CD-Audio/Video (CD-A/V)

and CD-Read/Write (CD-R/W) discs

• Equalizer for optimal performance

• Fully Automatic Laser Power Control (ALPC) including

stabilization plus a separate laser supply voltage for power efficiency

• Adjustable current range of ALPC output

• Automatic N- or P-substrate monitor diode selection

• Adjustable laser bandwidth and laser switch-on current

slope using external capacitor

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

• Optimized interconnection between data amplifier and Philips’ digital signal processor CD10LC (SAA7325)

• Wide supply voltage range

• Power-down switch to reduce power consumption

during standby

• Low power consumption.

GENERAL DESCRIPTION

The TZA1025 is a data amplifier and laser supply circuit for voltage output mechanisms found in a wide range of audio and video CD systems. The device contains an RF amplifier and an automatic laser power control circuit.

The RF bandwidth allows this device to be used in CD-A/V applications with a data rate of n = 1 times speed. The RF gain can be adapted for CD-A/V discs or CD-R/W discs by means of the gain select signal.

The equalizer ensures an optimal performance. The TZA1025 can be adapted to a wide range of voltage

output mechanisms by means of external resistors. The ALPC circuit will maintain control over the laser diode

current. With an on-chip reference voltage generator, a constant and stabilized output power is ensured independent of ageing. The ALPC can accommodate N- or P-substrate monitor diodes.

A separate supply voltage connection for the laser allows the internal power dissipation to be reduced by connecting a low voltage supply. The laser output current range can be optimized to fit the requirements of the laser diode by means of one external resistor. When a DC-to-DC converter is used, in combination with the control loop of the ALPC, the adjustable output current range provides the possibility to compensate for the extra gain a DC-to-DC converter introduces in the control loop.

TZA1025

The preamplifier forms an interface for voltage output CD mechanisms to the Philips’ digital signal processor CD10LC (SAA7325).

ORDERING INFORMATION

TYPE

NUMBER

TZA1025T SO14 plastic small outline package; 14 leads; body width 3.9 mm SOT108-1

1998 Oct 30 2

NAME DESCRIPTION VERSION

PACKAGE

Philips Semiconductors Product speciﬁcation

Data ampliﬁer and laser supply circuit for CD

TZA1025

audio and video optical systems (ADALASLC)

QUICK REFERENCE DATA

SYMBOL PARAMETER CONDITIONS MIN. TYP. MAX. UNIT

Supplies

DD(L)

RF ampliﬁer

d(f)(RF)

Laser supply circuit

o(LASER)(max)

i(mon)

Temperature range

amb

supply voltage 2.4 − 5.5 V supply current − 3 − mA laser supply voltage 2.4 − 5.5 V

RF ﬂatness delay −− 10 ns

maximum laser output current V

DD(L)

− V

o(LASER)

= 0.55 V 80 −−mA

monitor input voltage

N-substrate monitor diode − 0.150 − V P-substrate monitor diode − V

− 0.150 − V

operating ambient temperature 0 − 70 °C

BLOCK DIAGRAM

handbook, full pagewidth

CDRW

DIN

MON

GND

RFFB

TZA1025

V/I

GND

GAP

(1)

V/I

DD(L)

250 kHz

MBK902

3 7

RFEQO

CMFB

RGADJ CFIL

PWRON

(1) Band gap reference voltage.

Fig.1 Block diagram.

1998 Oct 30 3

Philips Semiconductors Product speciﬁcation

Data ampliﬁer and laser supply circuit for CD audio and video optical systems (ADALASLC)

PINNING

SYMBOL PIN DESCRIPTION

LD 1 current output to laser diode V

DD(L)

2 laser supply voltage CFIL 3 external ﬁlter capacitor MON 4 laser monitor diode input DIN 5 central diode input GND 6 ground PWRON 7 power-on select input CMFB 8 common mode feedback voltage

input RFFB 9 external RF feedback resistor RFEQO 10 RF ampliﬁer output CDRW 11 gain select input for CD-A/V, CD-R/W GND 12 ground V

13 supply voltage

RGADJ 14 external laser supply gain adjust

resistor

The gain of the RF amplifier can be adjusted by the external input resistors. Fig.3 shows the simplified schematic which can be used to determine the RF gain. The signal is AC coupled to the RF amplifier. The formula to determine the gain is shown below:

where:

GRF is the RF amplifier gain n is the number of input resistors Z R2 is the value of the input resistors (Ω).

The gain can be increased by a factor of 4 by making pin CDRW HIGH. The value of Z (CDRW = LOW) and 38 kΩ for CD-R/W (CDRW = HIGH).

An internal equalizer ensures an optimal performance. The DC output level of the amplifier can be set by applying

a DC voltage on the common mode feedback pin CMFB. Since the input signal is AC-coupled the RF output voltage will swing (symmetrically) around this DC level.

tr RF()

n–

×=

-----------------R2

is the transimpedance of the amplifier (Ω)

tr(RF)

is 9.8 kΩ for CD-A/V

tr(RF)

TZA1025

(1)

handbook, halfpage

DD(L)

CFIL

MON

DIN

GND

PWRON

1 2 3 4 5 6 7

TZA1025

MBK901

14 13 12 11 10

9 8

RGADJ V

GND CDRW RFEQO RFFB CMFB

Fig.2 Pin configuration.

FUNCTIONAL DESCRIPTION

The TZA1025 consists of two sections, the RF amplifier and the automatic laser power control circuit.

RF ampliﬁer

The RF amplifier consists of a current input amplifier, an equalizer/bandwidth section and a transimpedance output amplifier with an external feedback resistor of 10 kΩ(fixed value).

The coupling of the TZA1025 to the signal processor (SAA7325) can be either AC or DC. When an AC-coupling is chosen (see Fig.6) the minimum supply voltage can be applied. When a DC-coupling is chosen (see Fig.7) a minimum supply voltage of 2.8 V is required.

10 kΩ

CDRW

RFEQO

MGL530

handbook, halfpage

R2(1) R2(2)

R2(n)

Fig.3 Simplified schematic.

1998 Oct 30 4

Philips Semiconductors Product speciﬁcation

Data ampliﬁer and laser supply circuit for CD audio and video optical systems (ADALASLC)

Automatic laser power control circuit

The ALPC stabilises the laser output power thereby reducing the effect of ageing of the laser.

The TZA1025 automatically detects when an N- or P-substrate monitor diode is used and selects the correct reference voltage. A simplified diagram for the use of an N- or P-substrate monitor diode is given in Fig.4.

The gain of the loop can be controlled (reduced) by adding an external resistor between pins RGADJ and GND. The loop gain then becomes:

loop

× G

ALPCGlm

con

250

×=

------------------------------------250 R

RGADJ

where:

is the loop gain

loop

is the ALPC transfer (60 A/V)

ALPC

Glm is the laser-to-monitor transfer (V/A) G

is the extra gain introduced when a DC-to-DC

con

converter is used in the loop; G

= 1 when no

con

DC-to-DC converter is used 250 is a fixed internal resistor value (Ω) R

is the value of the external resistor (Ω).

RGADJ

The minimum available output current is also reduced when an external resistor is used. The formula to determine the minimum available output current is shown in equation (3).

oIo(LASER)(max)

250

×=

------------------------------------250 R

RGADJ

where:

o(LASER)(max)

250 is a fixed internal resistor value (Ω) R

The bandwidth of the loop is determined by the external filter capacitor C determine the bandwidth is shown in equation (4).

-3dB

(2)

where:

C G

The TZA1025 has a protection circuit to prevent laser damage that can occur due to a dip of V occurs the output transistor (see Fig.4) will go into saturation making it unable to supply the required laser current. Without the protection circuit the ALPC would still try to supply the required laser current by charging the filter capacitor C would create a large output current during the few milliseconds it needs to discharge the capacitor to a normal level. The protection circuit monitors the output transistor and switches off the ALPC when saturation occurs by discharging the capacitor. The ALPC will automatically restart within a few milliseconds after the dip

(3)

has passed.

is output current (mA)

is the maximum laser output current (mA)

is the value of the external resistor (Ω).

RGADJ

and the loop gain. The formula to

CFIL

----------------------------------------- -

is the value of the capacitor (F)

CFIL

is the loop gain.

loop

16 106⋅×

CFIL

loop

. After the dip a fully charged capacitor

CFIL

TZA1025

. When a dip

DD(L)

(4)

handbook, full pagewidth

150 mV

DD(L)

CFIL

DC-TO-DC

CONVERTER

a. N-substrate monitor diode. b. P-substrate monitor diode.

Fig.4 Automatic Laser Power Control (ALPC) loop.

1998 Oct 30 5

VDD − 150 mV

DD(L)

CFIL

DC-TO-DC

CONVERTER

MGR519

+ 11 hidden pages