Ensuring sufficient bias current is provided to a portion of a circuit containing low voltage transistors operating with a high supply voltage. Such a sufficient bias current may be ensured by generating a primary bias current from a low supply voltage and a backup bias current from a high supply voltage, and providing the backup bias current as the bias current if the primary bias current is not present. The primary bias current may be provided as the bias current when the low supply voltage is available. Thus, the backup bias current is provided as bias current in case of undesirable supply sequencing.
Transistors of low voltage specification are used to process information in a signal received at a high(er) voltage level. A protection circuit ensures that the cross terminal voltages do not exceed an allowed maximum voltage (e.g., 2.4 V for transistors of 1.8V specification). In an embodiment, the protection circuit contains a PMOS transistor which turns off if a protected cross terminal voltage exceeds such allowed maximum voltage. As a result, protection may be provided while consuming minimal power. The protection circuit may be employed in various types of circuits such as input buffers and logic gates. The protection circuits and the input buffers may potentially be implemented using transistors of a single voltage specification.
