Pulse width modulation is a proven and increasingly popular method for controlling gray scale and/or resolution enhancement in laser printers. The AD9560 provides a one-chip solution to pixel-by-pixel control, which yields much greater true resolution than "super pixel" techniques that are in use in present generation printers. High resolution is possible without significant increase in dot clock frequency which is necessary for "super pixel" methods.
Super pixel graphics, in effect, "trick the eye" by scattering different size pixels in varying densities. At a distance, these images appear to have high quality gray scale characteristics. Upon close inspection, a similar graphic utilizing pixel-by-pixel modulation demonstrates that resolution has been compromised to obtain gray scale.
In a basic laser printer or copier, the laser diode is either "on" or "off" for any pixel period. By utilizing the AD9560 ahead of the laser diode, each pixel can be controlled to increments equal to 1/256 of the pixel period. With the additional on-chip placement control (i.e., center, leading, and trailing edge modulation), 764 different pulse size/position options are theoretically possible.
For images containing text and graphics, mixed-mode operation may be required. The pulse with modulation feature of the AD9560 is disabled simply by inputting the codes 00 H and FF H . The output will be logic zero logic one respectively for the entire clock cycle.
The AD9560 pulse width modulator is fully self-contained, requiring only a single resistor (R SET ) to match the nominal full-scale range to the DOT CLOCK. An on-chip autocalibration circuit fine tunes the range and compensates for lot-to-lot variation of on-chip timing circuits.
With autocalibration and SOIC packaging the AD9560 is well suited for volume, automated assembly. In addition to 28-lead SOIC (AD9560KR), 28-pin P-DIP (AD9560KN) is also available. Both devices are rated over the commercial temperature, 0°C to +70°C.