TZA1025 datasheet(4/16 Pages) PHILIPS | Data amplifier and laser supply circuit for CD audio and video optical systems ADALASLC

4 page

1998 Oct 30

Philips Semiconductors

Product speciﬁcation

Data ampliﬁer and laser supply circuit for CD

audio and video optical systems (ADALASLC)

TZA1025

PINNING

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 k

Ω (fixed

value).

SYMBOL

DESCRIPTION

current output to laser diode

VDD(L)

laser supply voltage

CFIL

external ﬁlter capacitor

MON

laser monitor diode input

DIN

central diode input

GND

ground

PWRON

power-on select input

CMFB

common mode feedback voltage

input

RFFB

external RF feedback resistor

RFEQO

RF ampliﬁer output

CDRW

gain select input for CD-A/V, CD-R/W

GND

ground

VDD

supply voltage

RGADJ

external laser supply gain adjust

resistor

Fig.2 Pin configuration.

handbook, halfpage

MBK901

TZA1025

VDD(L)

CFIL

MON

DIN

GND

PWRON

CMFB

RFFB

RFEQO

CDRW

GND

VDD

RGADJ

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:

(1)

where:

GRF is the RF amplifier gain

n is the number of input resistors

Ztr(RF) is the transimpedance of the amplifier (Ω)

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 Ztr(RF) is 9.8 kΩ for CD-A/V

(CDRW = LOW) and 38 k

Ω 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.

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.

–

tr RF

()

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

Fig.3 Simplified schematic.

handbook, halfpage

CDRW

RFEQO

10 k

Ω

Vin

R2(1)

R2(2)

R2(n)

Vin

MGL530

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