Patent ID: 7471064

Claim:
A circuit system comprising: a plurality of circuit blocks, each including a circuit driven to operate by a power supply voltage in one of a plurality of voltage ranges obtained as a result of delimiting the voltage range of a predetermined power supply; signal propagation transistors each used for propagating a signal output by a first circuit pertaining to a specific one of the circuit blocks to a second circuit pertaining to another one of the circuit blocks; and a voltage-setting means for setting a voltage applied to a particular one of the signal propagation transistors at a magnitude smaller than a breakdown voltage of the particular signal propagation transistor, wherein the voltage applied is further associated with a difference between a first electric-potential associated with the first circuit and a second electric-potential associated with the second circuit, the difference including a voltage drop of the voltage-setting means, the difference being greater than a breakdown voltage of the particular one of the signal propagation transistors, and the voltage-setting means for setting a voltage applied to a particular one of the circuit block includes a series circuit including a current generator and a Zener diode, which are connected between a higher electric-potential side and a lower electric-potential side of the particular circuit block, and a voltage-setting transistor, which has a control terminal connected to the anode of the Zener diode and is connected in series between the higher electric-potential side of the particular circuit block and the signal propagation transistor.