Patent ID: 8038238

Claim:
An inkjet printhead substrate to which a first power supply voltage to be used for conducting current to an electrothermal transducer generating heat energy for discharging liquid, and a third power supply voltage to be used for operating a logic circuit for generating a driving signal for driving the electrothermal transducer are applied from outside, the inkjet printhead substrate comprising: the electrothermal transducer; the logic circuit; a switching element configured to control whether to conduct current to the electrothermal transducer, based on the driving signal; a converting circuit configured to amplify a first amplitude of a driving signal output from the logic circuit to a second amplitude necessary for an operation of the switching element; and a power supply voltage generating circuit configured to generate a second power supply voltage to be used for amplifying the first amplitude to the second amplitude from the first power supply voltage, only at a timing when the third power supply voltage is applied, wherein the power supply voltage generating circuit includes a ground circuit causing an output voltage to converge to a GND potential when applying of the third power supply voltage is stopped.