Patent ID: 6054888
Filing Date: 2000-04-25
Classification: H03K

Abstract:
A level shifter for shifting a core range of core input voltage between a low core voltage and a high core voltage to a shifted range between a low shifted voltage and a high shifted voltage, while limiting voltage across terminals of devices within said level shifter, said level shifter comprising:a first shifting stage including:a first pull-up stack of a first plurality of pull-up devices, coupled between a high power supply and a first coupling node, the first plurality of pull-up devices turning on when the first coupling node is driven to the high shifted voltage that is substantially the voltage at the high power supply and turning off when the first coupling node is driven to the low shifted voltage that is substantially the voltage at a low power supply, wherein a voltage difference between the first coupling node and the high power supply is distributed across said first plurality of pull-up devices when the first coupling node is driven to the low shifted voltage;a first pull-down stack of a first plurality of pull-down devices, coupled between the low power supply and the first coupling node, the first plurality of pull-down devices turning on when the first coupling node is driven to the low shifted voltage and turning off when the first coupling node is driven to the high shifted voltage, wherein a voltage difference between the first coupling node and the low power supply is distributed across said first plurality of pull-down devices when the first coupling node is driven to the high shifted voltage; anda first clamping circuit, coupled to the first coupling node and to a first predetermined node of the first plurality of pull-up and pull-down devices, for limiting voltage across terminals of each of the first plurality of pull-up and pull-down devices by discharging down said first predetermined node when the first coupling node is driven to the low shifted voltage and by charging up said first predetermined node when the first coupling node is driven to the high shifted voltage; andsaid level shifter further comprising a second shifting stage including:a second pull-up stack of a second plurality of pull-up devices, coupled between the high power supply and a second coupling node, the second plurality of pull-up devices turning on when the second coupling node is driven to the high shifted voltage and turning off when the second coupling node is driven to the low shifted voltage, wherein a voltage difference between the second coupling node and the high power supply is distributed across said second plurality of pull-up devices when the second coupling node is driven to the low shifted voltage;a second pull-down stack of a second plurality of pull-down devices, coupled between the low power supply and the second coupling node, the second plurality of pull-down devices turning on when the second coupling node is driven to the low shifted voltage and turning off when the second coupling node is driven to the high shifted voltage, wherein a voltage difference between the second coupling node and the low power supply is distributed across said second plurality of pull-down devices when the second coupling node is driven to the high shifted voltage; anda second clamping circuit, coupled to the second coupling node and to a second predetermined node of the second plurality of pull-up and pull-down devices, for limiting voltage across terminals of each of the second plurality of pull-up and pull-down devices by discharging down said second predetermined node when the second coupling node is driven to the low shifted voltage and by charging up said second predetermined node when the second coupling node is driven to the high shifted voltage;and wherein one of the first plurality of pull-up devices is cross-coupled to one of the second plurality of pull-up devices, and wherein the core input voltage is coupled to one of the first plurality of pull-down devices, and wherein the core input voltage is coupled via an inverter to one of the second plurality of pull-down devices,such that the first coupling node is driven to the low shifted voltage and the second coupling node is driven to the high shifted voltage when the core input voltage is the high core voltage, and such that the first coupling node is driven to the high shifted voltage and the second coupling node is driven to the low shifted voltage when the core input voltage is the low core voltage,and wherein the shifted range between the low shifted voltage and the high shifted voltage is higher than the core range between the low core voltage and the high core voltage.