U8601B

The U8601B has the following features including General purpose analog and digital modulation inputs;On-chip generation of 3 power levels for read, erase,and write operations;Control of power, pulse width and mode parameters by serial 3-wire interface;External set resistor for basic power level;Supervision of power supply, laser current and laser power;Laser shutdown to prevent laser damage and data loss;Idle mode for power saving;Single+5 V power supply;Master clock range 24 MHz to 38 MHz;Noise reduction by servo loop and weak high frequency modulation.

The U8601B is a very high-speed laser controller circuit for rewritable optical disk systems. U8601B comprises servo amplifier, high frequency modulator, power generators, pulse width generators, serial interface, and operation control unit.The wideband and high-gain Servo Amplifier drives the laser diode up to 180 mA. U8601B performs noise reduction of the laser by a feedback loop via optical path and monitor diode. The reference input current for the servo loop is digitally controlled by power and pulse width generators.For reduction of laser mode hopping noise during read mode, the High Frequency Modulator adds a weak modulation current with 288 to 456 MHz and a maximum swing of 5 mA.Three Power Generators define read, erase, and write power levels with 4-bit resolution each.Read and write actions are controlled by write gate(WGATE), write data (DATAINl), writing flag (M3T),and the master clock (MCLK).Besides the built-in write pulse generation, external digital modulation (mode DEM) as well as external analog modulation (Pin EXTM) are possible.Parameters for power, pulse widths, and mode sets are programmed via the Serial Interface. Data packets of 16 bit length of U8601B can be received with a maximum clock rate of 10 MHz. Reception is acknowledged by a  17th serial bit.

The servo amplifier U8601B drives the optical power of the laser diode  according  to  the  reference  current, iref.  The feedback loop is closed through the optical path and the photo diode which monitors the actual laser power.The comparison of photo current, ipd, and reference current, iref, is performed within a transimpedance input stage, yielding low input impedance and biasing voltage for the operation of the grounded photo diode. For symmetry reasons a capacitor U8601B should be connected to the Pin IREF, corresponding to the total capacitance of photo diode and stray capacitance at the Pin PDK. This will improve bandwidth and noise.