A model for the parasitic SCR in bulk CMOS

A model is presented for the parasitic SCR in bulk CMOS. The model shows the exact way that the shunting resistances alter the terminal V-I characteristics. It describes a negative differential resistance (NDR) range which is the only requirement for latch-up if certain biasing conditions are met. The NDR region will start when the product of current and shunting resistance equals the built in voltage and will occur for an+ ap< 1 (or βnβp< 1). The conditions for the center junction to become forward biased are given. If these conditions are met, the SCR will latch-up. If these conditions are not met, latch-up becomes dependent on the biasing circuit.