Sub-micron high input voltage tolerant input output (I/O) circuit
View Patent ↗A method of providing bias voltages for input output connections on low voltage integrated circuits. As integrated circuit voltages drop generally so does the external voltages that those circuits can handle. By placing input and output devices, in series, external voltages can be divided between the devices thereby reducing junction voltages seen by internal devices. By using external voltages as part of a biasing scheme for integrated circuit devices, stress created by the differential between external voltages and internal voltages can be minimized. Additionally device wells can be biased so that they are at a potential that is dependant on the external voltages seen by the low voltage integrated circuit.
1. An apparatus for generating a bias voltage at a bias node, the apparatus comprising:
a first input for accepting a pad voltage from an input/output circuit;
a second input for accepting an output enable signal;
a third input for accepting a first input voltage;
an output circuit for providing the first input voltage to the bias node when the output enable signal is at an enable value;
a fourth input for accepting a second input voltage; and
a threshold transistor coupled to the bias node at an output of the threshold transistor, wherein the bias voltage at the bias node is between the first input voltage plus a threshold voltage of the threshold transistor and the second input voltage minus the threshold voltage of the threshold transistor.
2. The apparatus of claim 1 , wherein the threshold transistor comprises a P-channel Metal Oxide Semiconductor (PMOS).
3. An apparatus for generating a bias voltage at a bias node, the apparatus comprising:
a first input for accepting a pad voltage from an input/output circuit;
a second input for accepting an output enable signal;
a third input for accepting a first input voltage;
an output circuit for providing the first input voltage to the bias node when the output enable signal is at an enable value;
a fourth input for accepting a second input voltage, wherein the bias voltage at the bias node is between the first input voltage plus a first offset voltage and the second input voltage minus a second offset voltage.
4. The apparatus of claim 3 , wherein the first offset voltage is equal to a threshold voltage of an N-channel Metal Oxide Semiconductor (NMOS) and wherein the second offset voltage is equal to a threshold voltage of a P-channel Metal Oxide Semiconductor (PMOS).
5. The apparatus of claim 3 , wherein the first offset voltage is equal to a threshold voltage of a P-channel Metal Oxide Semiconductor (PMOS) and wherein the second offset voltage is equal to a threshold voltage of an N-channel Metal Oxide Semiconductor (NMOS).
6. The apparatus of claim 3 , wherein each of the first offset voltage and the second offset voltage is equal to a threshold voltage of a P-channel Metal Oxide Semiconductor (PMOS).
7. The apparatus of claim 3 , wherein the second input voltage is about 3.3 Volts.
8. The apparatus of claim 7 , wherein the first input voltage is between about 3.3 Volts and 1.2 Volts.