
1998 Oct 30
5
Philips Semiconductors
Product specication
Data amplier and laser supply circuit for CD
audio and video optical systems (ADALASAuto)
TZA1026
PINNING
FUNCTIONAL DESCRIPTION
The TZA1026 consists of two sections, the RF amplifier
and the automatic laser power control circuit.
RF amplier
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
(fixed
value).
SYMBOL
PIN
DESCRIPTION
LD
1
current output to laser diode
VDD(L)
2
laser supply voltage
CFIL
3
external lter 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 amplier output
CDRW
11
gain select input for CD-A/V, CD-R/W
EQSEL
12
equalizer/speed select input
(n = 1, 2 or 4)
VDD
13
supply voltage
RGADJ
14
external laser supply gain adjust
resistor
Fig.2 Pin configuration.
handbook, halfpage
MBK890
TZA1026
1
2
3
4
5
6
7
8
14
13
12
11
10
9
LD
VDD(L)
CFIL
MON
DIN
GND
PWRON
CMFB
RFFB
RFEQO
CDRW
EQSEL
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 ()
R2 is the value of the input resistors(
).
The gain can be increased by a factor 4 by making
pin CDRW HIGH. The value of Ztr(RF) is 9.8 k for CD-A/V
(CDRW = LOW) and 38 k
for CD-R/W (CDRW = HIGH).
The equalizer/bandwidth section can be switched between
n = 1, n = 2 (inclusive the corresponding equalizer) or
n = 4 (inclusive the required bandwidth limitation) times
speed.
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 TZA1026 to the signal processor
(SAA7326) can be either AC or DC. When an AC-coupling
is chosen (see Fig.8) the minimum supply voltage can be
applied. When a DC-coupling is chosen (see Fig.9) a
minimum supply voltage of 2.8 V is required.
G
RF
n
–
Z
tr RF
()
R2
------------------
×
=
Fig.3 Simplified schematic.
handbook, halfpage
CDRW
RFEQO
C2
10 k
Vin
R2(1)
R2(2)
R2(n)
Vin
MGL530