A BiCMOS thermal head intelligent driver with density controllers for full-tone rendition printers

A 3- mu m BiCMOS thermal head driver using pulsewidth modulation dealing with eight-bit density input data (256 gray levels) is described. Circuits composed of 64*8-bit complex counters, which function as eight-line parallel 64-bit shift registers (shift mode) and as 64 counters which have eight bits (count mode) by alteration of their mutual connections according to the mode signals, have been developed. The complex counter controls the output pulse width according to the binary data and the clock intervals (minimum 100 ns). The shift registers can operate using a 20-MHz clock. The driver consists of about 4500 CMOS gates and 128 bipolar transistors in a 2.8-mm*8.8-mm chip size. The breakdown voltage of the bipolar transistor BV/sub cbo/ is more than 35 V. The driver is especially suited for full-tone rendition printers. Applications of the driver include use in thermal print heads, LED print heads, and LCD print heads.<
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