Transcript
New Semiconductor Products for Laser Printers and Copiers
New 4-beam Lasers and Laser Drivers for High-performance Laser Printers and Copiers Copiers and laser pr inters use electrophotographic technology that prints using the following five processes: (1) Charging, (2) Exposing, (3) Developing, (4) Transferring and (5) Fixing. (See figure 1.) A semiconductor laser is indispensable to the (2) Exposing process. In the exposing process, a polygon mirror reflects a laser beam to irradiate and scan a photoreceptor. (See figure 2.) Print speed and resolution are important performance indicators for copiers and laser printers. Print speed can be increased mechanically by raising polygon mirror rotation or using multi-faceted mirrors, or optically by using a multiple beam system that simultaneously scan multiple laser beams. Sony has already conducted more than 10 years of research in multibeam lasers for the latter system. Sony holds a 55% or larger share∗1 of the multibeam laser printer market and an 87% or larger share∗1 of highperformance multibeam systems involving four or more beams, which show the respect our products enjoy. Printers with four or more beams used to be high-end systems. However, the demand
4-Beam Common-Anode Laser Diode
SLD268MS
4-Beam Common-Anode Laser Driver
CXA3814R
Figure 1
Figure 2
Electrophotographic Technology
for higher speeds and higher resolutions is expected to raise the share of such printers. To meet this demand, Sony has newly developed the SLD268MS, a compact, 4-beam commonanode laser diode and the CXA3814R, 4-beam common-anode laser driver, which maximizes the potential of the laser. Thanks to technology developed by Sony, the design of a drive circuit tailored to laser device characteristics and the combination of the the laser and driver in a product made it possible to simplify a board design that fully utilizes its characteristics. ∗1: As of January, 2012 (based on Sony's research)
Scanning Photoreceptor
Laser light source
f-θ lens
(2) Exposing (1) Charging (3) Developing
Laser light source
Toner
Photoreceptor (5) Fixing Paper (4) Transferring
Polygon mirror
4-Beam Common-Anode Laser Diode
SLD268MS Sony's unique SDH structure has allowed us to fit a low threshold current laser in a compact 5.6 mm diameter package to produce a new generation 4-beam laser with even more advanced high-performance and cost-effectiveness 30 µm pitch 4-beam laser
The SLD268MS incorporates the following new technologies to provide greater quality.
Sony provides a lineup of light sources for copiers and laser printers that ranges from single-beam to 8-beam lasers. As the number of beams increases, the characteristics drop due to greater heat generation. To better cool the laser, it used to be placed in a large package, but this became a cost barrier that made it difficult to introduce lasers with four or more beams to a wider market. Improvements in Sony's SDH structure lowered the threshold current resulting in less generated heat and made it possible to integrate the laser in a more compact package. (See photograph 1.) This achievement is expected to increase the market appeal of 4-beam laser products.
■ Crystal Growth Process In the SDH structure, a crystal growth is formed on a specially processed GaAs substrate in a single crystal growth process that produces the laser structure. The currentblocking layer blocks current more efficiently than other structures. The formation of the block layer is a vital characteristic of this structure where the selection of a dopant is essential in improving its current control characteristics. The SLD268MS uses a new type of dopant that produces a more stable current block layer structure. (See figure 3.)
Threshold current value: 4 mA Rated optical power output/maximum optical power output: 10 mW/15 mW 5.6 mm diameter 6-pin package
Figure 3
Comparison of 9 mm Diameter and 5.6 mm Diameter (SLD268MS)
Figure 4
SDH Structure n-cap layer
50
n-clad layer
40
Active layer
Current block layer p-cap layer
GaAs substrate
Photograph 2
Operating current [mA]
Photograph 1
Three-dimensional Interconnection
Reliability Data
30 20 10 0
0
200
400
600 Time [h]
800
1000
1200
■ Electrode Formation Process In 4-beam lasers made so far, the solder electrodes independently controlled each beam. However, the SLD268MS has an air bridge, a multilayer interconnection technology, to obtain greater stability in the narrow pitch process.
■ Wire Formation Process Five types of wire bonds are required in a 4-beam laser if PD wires are included. Compact φ5.6 mm packages require much finer wire than that used in existing φ9 mm packages. The numerous environmental tests that the SLD268MS has been put through have confirmed the strength of the highquality wire bonding. (See photograph 2.)
4-Beam Common-Anode Laser Driver
CXA3814R Adapting laser driver drive circuits for optical discs has endowed the CXA3814R with high resolution, low power consumption and compact size Built-in 10-bit electronic volume for light quantity control
The CXA3814R is a 4-beam common-anode laser driver. The input of photodiode (PD) current for monitoring light quantity is used for building the auto power control (APC) system that comprises the sample hold circuit and the laser drive current control circuit of the driver. This driver can operate a 4-beam laser and in combination with multiple products and by connecting PD mirror current between drivers, it is possible to drive multi-channel and multibeam lasers with 8 or more beams. It can also drive single lasers and 2-beam lasers.
Built-in snubber circuit for adjusting laser drive current waveform Built-in memory for saving adjustment values Low power consumption and compact size
Figure 5
Block Diagram
CXA3814R Power monitor error detection
Development team members (From left, back row) Tetsuya Hirama, Fumitake Oikawa, Eiji Takase, Kazuki Wakatsuki, Sachio Karino and (front row) Shoji Honda
Serial communication signal
Register • Electronic volume setting • Snubber setting • Memory communication setting
Error detection signals Laser power monitor Memory • Electronic volume setting data • Snubber setting data • Memory status data Laser power supply
Light quantity setting voltage Channel 1 to 4
10-bit electronic volume
PD current mirror
Print data signal Channel 1 to 4
APC & sample-and-hold circuit
Laser driver
Sample-and-hold signal Channel 1 to 4
Internal snubber
PD mirror current
SLD268MS
■ Built-in 10-bit Electronic Volume for Light Quantity Although external volume resistors are used for adjusting the APC light quantity, the CXA3814R comes with a built-in 10-bit electronic volume that can adjust PD input current in a range of 1 to 12 times in 1.2% steps, which greatly improves the precision of light quantity control. This function also helps reduce the number of parts used to control light quantity in a multibeam laser. PD input current has a wide input range of 40 μA to 4.8 mA to accommodate various laser types.
■ Built-in Snubber Circuit for Adjusting Laser Drive Current Waveform Since drive current of the laser driver varies with the impedance characteristics of the laser and the set board design, a drive current adjusting circuit may be required during set design. An increase in the number of laser beams increases the number of parts in the drive current adjusting circuit. The CXA3814R has a built-in snubber circuit
to reduce the number of parts for adjusting drive current. The snubber circuit consists of resistors and capacitors that each enable selection of 4-value constants to allow selection of the optimum waveform from 16 drive waveforms. (See figure 6.)
■ Built-in Memory for Saving Adjustment Values Register settings of the electronic volume and the snubber circuit can be performed via serial communication. The CXA3814R is provided with a builtin memory for storing register settings so that customers that do not have free space in the set system can take advantage of CXA3814R adjustment functions. Of course, data can be stored in any existing memory in the set system instead of internal memory. Data can be written to memory using serial communication and once data is in memory, it is automatically loaded in the register when the CXA3814R is powered on. Data loaded in memory can be read using a suitable serial communication readout mode.
■ Low Power Consumption and Compact Size Use of CMOS circuits in the CXA3814R has substantially reduced current consumption. A power supply voltage of 3.3 V has also helped lower power consumption. The CMOS circuits in the CXA3814R have shrunk chip size while the circuit system and the electronic volume function have reduced the number of pins to produce a 48-pin package with 4 channels.
Development team members (From left) Motokazu Saeki, Takahiro Tsukada and Takeshi Yuwaki
Figure 6
Snubber Circuit Effect
Drive current when snubber circuit is off f = 50 MHz, Isw = 25 mA
Drive current at max snubber setting f = 50 MHz, Isw = 25 mA
