LA9703W_06 Datasheet, PDF (6/16 Pages) Sanyo Semicon Device – Front End Processor for DVD Player

LA9703W
(8) DPD circuit
This circuit compares the phase of the pin 3 input signal to the pin 4, 5, 6, and 7 input signals and outputs the result from
pin 40. The phase compared signal is output as a current signal by the pin 37 constant-current charge pump, and
converted to a voltage level by the external capacitor and resistor attached to pin 37. The signal converted to a voltage
is passed through a buffer amplifier and, after band limiting is applied by the band switching circuit, is output from pin
40. The charge pump is set to its off mode by a high level on pin 30. The band switching circuit consists of a low-pass
filter whose frequency is 30kHz when pin 31 is at the high level and whose frequency is 200kHz when pin 31 is low.
Also, when pin 30 is at the low level, pin 37 is shunted to SREF.
(9) PP amplifier
The current signal input to pins 11 and 12 is converted to a voltage and after passing through a servo gain adjustment
VCA, the signal is band limited and output from pin 42. The signal output from pin 42 is input to pin 43 through a
capacitor and resistor. After this input signal is amplified, it is output from pin 41. This VCA, which adjusts the servo
gain, is controlled by the DC voltage applied to pin 32.
Note that pin 28 must be set to the low level if the PP amplifier is used.
(10) Wobble bandpass filter
The current signal input to pins 11 and 12 is converted to a voltage and the difference is taken. After passing through
the servo gain adjustment VCA, the signal is input to the bandpass filter. The DC component of the signal that was band
limited by the bandpass filter is removed with a DC cut circuit and, after being amplified by a 37dB amplifier, it is
output from pin 41. The fO frequency of the bandpass filter can be changed by changing the value of the external
resistor connected between pin 45 and ground.
When the value of the pin 45 external resistor is 62kΩ, fO will be about 200kHz. The cutoff frequency for the DC cut
circuit is set by the value of the capacitor connected to pin 44. The cutoff frequency will be approximately the product
of the internal resistance (18kΩ) and the value of the external capacitor.
Note that pin 28 must be set to the low level if the PP amplifier is used.
(11) APC circuit
A servo loop that holds the laser power at a fixed level is formed by inputting the monitor signal to pin 16 and
connecting pin 15 to the laser driver. The threshold voltage will be 180mV when pin 20 is low and (VCC - 1.5V) when
pin 20 is high. The laser can be turned off by setting pin 21 to the low level.
Note that there are two APC circuit systems; the second system consists of pins 18 (monitor input), 17 (laser drive), and
22 (laser on/off). The threshold voltage is 180mV.
(12) Reference circuit
The VCC level is resistor divided by two internally and that voltage is output from pin 58. The pin 58 voltage is a
dedicated reference voltage for the pickup.
The pin 48 voltage level is resistor divided by two internally and that voltage is output from pin 51. The pin 51 voltage
is a reference level that is supplied to the DSP and other circuits.
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