Integrated semiconductor circuits (ICs) can be damaged by transient pulses or overvoltages, which are coupled in via terminals (pads) or directly in lines, such that they become nonfunctional or are even destroyed. Such pulses or overvoltages may occur for example in the event of so-called electrostatic discharges (ESD). High voltages and high currents, associated with transient or ESD disturbances, cause high disturbing powers to occur.
Such a pulse (e.g. burst) may also occur in many fields of application, e.g. automotive engineering. In automotive engineering, by way of example, there is the requirement that circuits of this type which have to function in the high-voltage range up to 90 volts or above are also to be designed for significantly higher disturbance pulse levels.
For high-voltage applications produced by means of high-voltage processes, provision is usually made of protection devices that are initiated or triggered by an electrical breakdown. The breakdown voltages must be significantly greater than the maximum permissible operating voltages of the application circuit to be protected. Only then is it possible to guarantee an undisturbed functionality of the integrated circuit. In the case of a fault, e.g. when an impermissibly high voltage is present, this overvoltage is dissipated to reference potential or ground by the protection circuit and downstream assemblies are thus protected from the high voltage.
One alternative for such breakdown-based protection concepts is an active circuit for protecting an integrated circuit, comprising a combination of an active trigger circuit with a known protection device such as a thyristor or a bipolar or MOS protection transistor.
Active circuits for protecting the IC are often triggered by the rise of the transient signal. In this case, the signal rise per unit time is detected and a protection transistor or a protection circuit is turned on by means of a drive circuit.
In the case of a fault, the protection circuit may accordingly be understood as an actively triggered overvoltage or overcurrent surge arrestor. A fast activation of the protection circuit is necessary in the case of a fault.
Short switch-on times and a precise switch-on threshold of the protection circuit for the integrated circuit and the protective effect thereof for different forms of disturbance pulses are important aspects of the product specification and constitute a competitive advantage.
U.S. Pat. No. 5,982,601 discloses a thyristor (SCR—silicon control rectifier) for ESD protection, which is triggered directly by the transient signal. The thyristor is realized in the semiconductor arrangement in a manner known per se by means of an n-type well, a p-type well and highly doped n-type and p-type regions. The transient voltage is detected by means of an RC element. By means of inverters connected downstream, the voltage level detected at the capacitance is converted into a control signal which drives the base of the pap transistor of the thyristor structure. As soon as the output current of the then active pnp transistor generates a sufficiently large voltage drop at a resistor, the npn transistor of the thyristor structure turns on, so that the transient pulse is dissipated from the pad potential of the I/O pin to reference potential through the low-impedance thyristor path. The thyristor then automatically remains turned on until its current falls below the holding current and the turn-off condition is met.