Patent ID: 7597424
Filing Date: 2009-10-06
Classification: B41J

Abstract:
1. A printhead substrate comprising: a plurality of printing elements; a constant electric current source which generates a constant electric current used to drive said plurality of printing elements; a reference current generation circuit which generates in accordance with an externally input logic signal a reference current for generating the constant electric current; and a driving circuit which drives said plurality of printing elements by the constant electric current obtained by driving said constant electric current source in accordance with the reference current generated by said reference current generation circuit, wherein said reference current generation circuit includes: an n-bit shift register which receives and temporarily stores an n-bit logic signal; a latch circuit which latches the n-bit logic signal stored in the n-bit shift register; n driving circuits which generate electric currents of different levels; and an output circuit which outputs as the reference current a sum of the electric currents generated by the n driving circuits, and wherein the n driving circuits are selectively driven in accordance with the n-bit logic signal output from the latch circuit.