Printing element substrate and printhead

A printing element substrate comprising:

• a printing element;
• a switching element which drives said printing element based on an input control signal;
• a first current source which generates a predetermined current;
• a second current source which generates a current based on an input voltage;
• a current generation circuit which generates the control signal by amplifying a current obtained by adding a current generated by said second current source to a current generated by said first current source, and then generates the control signal by amplifying a current generated by said first current source;
• a first signal line which supplies a current from said printing element to said switching element;
• a second signal line which supplies a reference voltage;
• a third signal line which supplies the voltage of said first signal line to said second current source;
• and
• a first switch which is inserted in said third signal line and switches said third signal line between connection and disconnection based on a driving signal for designating driving of said printing element,
• wherein said first switch is controlled to a connected state when the driving signal for designating driving of said printing element is active and a disconnected state when the driving signal for designating driving of said printing element is inactive.