tza1025 NXP Semiconductors, tza1025 Datasheet - Page 4

• Manufacturer Part Number: tza1025
• Description: Data Amplifier And Laser Supply Circuit For Cd Audio And Video Optical Systems Adalaslc
• Manufacturer: NXP Semiconductors

Philips Semiconductors
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 (fixed
value).
1998 Oct 30
handbook, halfpage
LD
V
CFIL
MON
DIN
GND
PWRON
CMFB
RFFB
RFEQO
CDRW
GND
V
RGADJ
SYMBOL
DD(L)
DD
Data amplifier and laser supply circuit for CD
audio and video optical systems (ADALASLC)
PWRON
PIN
V DD(L)
10
12
13
14
11
1
2
3
4
5
6
7
8
9
MON
CFIL
GND
DIN
LD
Fig.2 Pin configuration.
current output to laser diode
laser supply voltage
external filter capacitor
laser monitor diode input
central diode input
ground
power-on select input
common mode feedback voltage
input
external RF feedback resistor
RF amplifier output
gain select input for CD-A/V, CD-R/W
ground
supply voltage
external laser supply gain adjust
resistor
1
2
3
4
5
6
7
TZA1025
MBK901
DESCRIPTION
14
13
12
11
10
9
8
RGADJ
V DD
GND
CDRW
RFEQO
RFFB
CMFB
4
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:
The gain can be increased by a factor of 4 by making
pin CDRW HIGH. The value of Z
(CDRW = LOW) and 38 k 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.
G
handbook, halfpage
RF
G
n is the number of input resistors
Z
R2 is the value of the input resistors ( ).
tr(RF)
RF
=
is the RF amplifier gain
–
is the transimpedance of the amplifier ( )
n
V in
V in
V in
Z
------------------
tr RF
R2
Fig.3 Simplified schematic.
R2(1)
R2(2)
R2(n)
C2
tr(RF)
10 k
CDRW
Product specification
is 9.8 k for CD-A/V
TZA1025
RFEQO
MGL530
(1)