Integrated circuit provided with a large area protection against electrostatic discharges
An integrated circuit protected against electrostatic discharges, including: first and second supply rails; first and second intermediary rails normally connected to the first and second supply rails; inverters formed of a P-channel MOS transistor series-connected to an N-channel MOS transistor, the sources of the P-channel and N-channel MOS transistors being respectively connected to the first and second supply rails and the bodies of the P-channel and N-channel transistors being respectively connected to the first and second intermediary rails; a positive overvoltage detector between the first and second supply rails; and a switch for connecting the first and second intermediary rails to the second and first supply rails when a positive overvoltage is detected.
1. An integrated circuit protected against electrostatic discharges, comprising:
first and second supply rails;
first and second intermediary rails normally connected to the first and second supply rails;
inverters, existing for the normal operation of the integrated circuit, formed of a P-channel MOS transistor series-connected to an N-channel MOS transistor, the sources of the P- and N-channel MOS transistors being respectively connected to the first and second supply rails and the bodies of the P- and N-channel MOS transistors being respectively connected to the first and second intermediary rails;
a positive overvoltage detector between the first and second supply rails; and
a switch for connecting the first and second intermediary rails to the second and first supply rails when a positive overvoltage is detected.
2. The integrated circuit of claim 1 , wherein the assembly of the positive voltage detector and of the switch comprises:
a resistor and a capacitor having a common connection node, series-connected between the supply rails;
a first inverter in series with a second inverter, the input of the first inverter being connected to said connection node, the first intermediary rail being connected to the output of the second inverter and the second intermediary rail being connected to the output of the first inverter;
a first diode forward-connected between the first intermediary rail and the first power supply rail; and
a second diode reverse-connected between the second intermediary rail and the second supply rail.
3. The integrated circuit of claim 2 , wherein the first and second diodes are formed of the parasitic diodes present in the first and second inverters.
4. The integrated circuit of claim 1 , wherein from 50 to 95% of the total surface area are taken up by the inverters.
5. A method for protecting against overvoltages in an integrated circuit having first and second supply rails, first and second intermediary rails, and inverters formed of a P-channel MOS transistor series-connected to an N-channel MOS transistor, the sources of the P-channel and N-channel MOS transistors being respectively connected to the first and second supply rails and the bodies of the P-channel and N-channel MOS transistors being respectively connected to the first and second intermediary rails, the method comprising the steps of:
detecting possible overvoltages between the first and second supply rails when the integrated circuit is not supplied;
connecting the first intermediary rail to the first supply rail and the second intermediary rail to the second supply rail when the integrated circuit is supplied or when the integrated circuit is not supplied and a negative overvoltage is detected; and
connecting the first intermediary rail to the second supply rail and the second intermediary rail to the first supply rail when the circuit is not supplied and a positive overvoltage is detected.