Laser head signal amplifier circuit for VCD-DVD player

Laser head signal amplifier circuit for VCD-DVD player

Laser head signal amplification circuits are mainly used in electronic products such as VCD/DVD players. The figure shows the
laser head signal amplification circuit of a typical VCD/DVD player . When
    the V CD / DVD player starts working, the microprocessor sends the start control signal to the automatic power control circuit that drives the laser diode, so
current flows through the laser diode, causing it to emit a laser beam. In order to stabilize the intensity of the laser beam emitted by the laser head,
a laser power detection diode is provided in the laser diode assembly. This diode is a photosensitive diode made together with the laser diode. It feeds back the detected
laser power signal to the automatic power control (APC) circuit. This negative feedback loop can automatically stabilize the luminous
power of the laser diode.
    It can be seen from the figure that the sum of the output signals of photodiodes A and C in the laser head is sent to the ③ pin of the preamplifier circuit, and the sum of the output signals of B and D
is sent to ④pin t of the preamplifier circuit, respectively, after being amplified and sent to the adder. The sum signal of A+B+C+D is formed, which is the RF signal, which contains
audio and video data signals. This signal is the main signal read from the optical disc, and is sent to the digital signal processing circuit and the decompression processing circuit.
Audio, video and auxiliary signals can be extracted on the road. The signals from pin @ and pin ④ are amplified and then subtracted to obtain the 1J focus error signal
. This signal is sent to the servo circuit and processed to form a control signal for driving the focus coil. The output signals of the photodiodes E and F in
    the laser head are amplified and then subtracted to obtain the tracking error signal. This signal
can be processed by the servo circuit to form the control signal of the tracking coil and the feed motor.