CXA1782CQ/CR
Description of Functions
RF Amplifier
The photo diode currents input to the input pins (PD1 and PD2) are each I-V converted via a 58kΩ equivalent
resistor by the PD I-V amplifiers. these signals are added by the RF summing amplifier, and the photo diode
(A + B + C + D) current-voltage converted voltage is output to the RFO pin. An eye-pattern check can be
performed at this pin.
1k
22k
3.3µ
RF_O
31
RF_M
32
A
C
58k
PD1
35
10k
10k
VA
VB
iPD1→
PD1 IV AMP
58k
B
D
RF SUMMING AMP
VC
VC
VC
PD2
36
iPD2→
PD2 IV AMP
The low frequency component of the RFO output voltage is VRFO = 2.2 × (VA + VB) = 127.6kΩ × (iPD1 + iPD2).
Focus Error Amplifier
The focus error amplifier calculates the difference between output VA and VB of the RF I-V amplifier, and
output current-voltage converted voltage of the photo diode (A + C – B – D).
25p
174k
32k
VB
– (B + D)
1
FEO
– (A + C)
VA
FE AMP
32k
25p
VC
87k
164k
FE_BIAS
VCC
37
VEE
47k
The FEO output voltage (low frequency) is VFEO = 5.4 × (VA – VB) = (iPD2 – iPD1) × 315kΩ.
Be aware that the rotation of the focus bias volume has reversed for the usual CD RF IC.
– 14 –
ETC [ ETC ]
