Dynamic bias circuit for driving low voltage I/O transistors
First Claim
Patent Images
1. A biasing circuit for driving a bias terminal of output buffer transistors that couple to an output node, comprising:
- a voltage swing limiting circuit coupled between a first power supply voltage and ground and having an output terminal coupled to the bias terminal,wherein, said voltage swing limiting circuit generates at its output terminal a bias signal whose voltage level varies dynamically between a first voltage and a second voltage in response to a signal on the output node.
2 Assignments
0 Petitions
Accused Products
Abstract
A bias circuit that generates a dynamic bias voltage for driving low-voltage transistors in an output buffer that interfaces with high-voltage signals is disclosed. Various circuits have been devised to ensure that no transistor in the bias and the output buffer circuitry undergoes voltages higher than that allowed by the fabrication process, even though the output signal voltage may swing well beyond the tolerable voltage levels. This is accomplished with minimal increase in power consumption and without compromising the speed of operation of the output buffer circuit.
-
Citations
25 Claims
-
1. A biasing circuit for driving a bias terminal of output buffer transistors that couple to an output node, comprising:
-
a voltage swing limiting circuit coupled between a first power supply voltage and ground and having an output terminal coupled to the bias terminal, wherein, said voltage swing limiting circuit generates at its output terminal a bias signal whose voltage level varies dynamically between a first voltage and a second voltage in response to a signal on the output node. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
-
-
11. A method for biasing cascoade transistors in an output buffer, comprising the steps of:
-
increasing a voltage level at a gate terminal of the cascode transistors to a first bias voltage when a signal at an output of the output buffer rises up toward a logic high level; and decreasing a voltage level at said gate terminal of the cascode transistors to a second bias voltage less than said first bias voltage, when said signal drops down toward a logic low level, wherein, the maximum voltage drop across the cascode transistors is limited to predetermined voltage during the rise and fall of the signal. - View Dependent Claims (12, 13, 14, 15)
-
-
16. An output buffer circuit comprising:
-
a first pull-up transistor coupled between an output node and a first intermediate node, and having a gate terminal coupled to receive a dynamic bias voltage; a second pull-up transistor coupled between the first intermediate node and a first power supply node, and having a gate terminal driven by internal logic; a first pull-down transistor coupled between the output node and a second intermediate node, and having a gate terminal coupled to receive the dynamic bias voltage; a second pull-down transistor coupled between the second intermediate node and a second power supply node, and having a gate terminal driven by internal logic; and a dynamic biasing circuit coupled between the first and second power supply nodes, and having an output coupled to gate terminals of the first pull-up transistor and the first pull-down transistor, wherein, the dynamic biasing circuit generates the dynamic bias voltage at its output whose voltage level varies dynamically in response to a signal at the output node. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25)
-
Specification