Power supply detection circuitry and method

Power supply detection circuitry, coupled to power supply means for supplying power to a processing circuit, comprising at least one power supply detecting means for detecting whether, when switching a supply voltage level of said power supply means from a first voltage level to a second voltage level, said supply voltage level has reached a predetermined voltage level, said power supply detecting means comprising:

• signal output means for outputting a ready signal indicating whether said supply voltage level has reached said predetermined voltage level;
• signal node means for carrying a signal node voltage level, said signal node being coupled to said signal output means, said signal output means outputting said ready signal in dependence on a signal node voltage level at said signal node means;
• first transistor means for coupling said power supply means and said signal node means;
• and
• second transistor means for coupling said signal node means and an external voltage supply means for supplying an external voltage level different from said supply voltage level;
• wherein:
• said first transistor means and said second transistor means are configured, when switching said supply voltage level from said first voltage level to said second voltage level, to compete with said first transistor means pulling said signal node voltage level towards said supply voltage level and said second transistor means pulling said signal node voltage level towards said external voltage level, said first transistor means being configured to overcome said second transistor means when said supply voltage level reaches said predetermined voltage level;
• and
• said signal output means is configured to output said ready signal in dependence on when said first transistor means overcomes said second transistor means.

Power supply detection circuitry, coupled to a power supply rail for a processing circuit, comprising at least one power supply detecting unit for detecting whether, when switching a supply voltage level of said power supply rail from a first voltage level to a second voltage level, said supply voltage level has reached a predetermined voltage level, said power supply detecting unit comprising:

• a signal output for outputting a ready signal indicating whether said supply voltage level has reached said predetermined voltage level;
• a signal node coupled to said signal output, said signal output outputting said ready signal in dependence on a signal node voltage level at said signal node;
• a first transistor coupled to said power supply rail and said signal node;
• and
• a second transistor coupled to said signal node and an external voltage supply having an external voltage level;
• wherein:
• said first transistor and said second transistor are configured, when switching said supply voltage level from said first voltage level to said second voltage level, to compete with said first transistor pulling said signal node voltage level towards said supply voltage level and said second transistor pulling said signal node voltage level towards said external voltage level, said first transistor being configured to overcome said second transistor when said supply voltage level reaches said predetermined voltage level;
• said signal output is configured to output said ready signal in dependence on when said first transistor overcomes said second transistor, wherein said ready signal has a ready state indicating that said supply voltage level has reached said predetermined voltage level and an unready state indicating that said supply voltage level has not reached said predetermined voltage level;
• and
• logic coupled between said signal node and said signal output, said logic being configured to switch said ready signal from said unready state to said ready state when said first transistor overcomes said second transistor to pull said signal node voltage level beyond a threshold voltage level, wherein a gate terminal of said second transistor is coupled to said logic such that said second transistor is switched off when said signal node voltage level is pulled beyond said threshold voltage level by said first transistor.

Power supply detection circuitry, coupled to a power supply rail for a processing circuit, comprising at least one power supply detecting unit for detecting whether, when switching a supply voltage level of said power supply rail from a first voltage level to a second voltage level, said supply voltage level has reached a predetermined voltage level, said power supply detecting unit comprising:

• a signal output for outputting a ready signal indicating whether said supply voltage level has reached said predetermined voltage level;
• a signal node coupled to said signal output, said signal output outputting said ready signal in dependence on a signal node voltage level at said signal node;
• a first transistor coupled to said power supply rail and said signal node;
• and
• a second transistor coupled to said signal node and an external voltage supply having an external voltage level;
• wherein:
• said first transistor and said second transistor are configured, when switching said supply voltage level from said first voltage level to said second voltage level, to compete with said first transistor pulling said signal node voltage level towards said supply voltage level and said second transistor pulling said signal node voltage level towards said external voltage level, said first transistor being configured to overcome said second transistor when said supply voltage level reaches said predetermined voltage level;
• and
• said signal output is configured to output said ready signal in dependence on when said first transistor overcomes said second transistor, comprising a plurality of said power supply detecting units, wherein said plurality of power supply detecting units comprise a chain of N power supply detecting units;
• said first transistor of a first power supply detecting unit in said chain is turned on in response to initiation of said switching of said supply voltage level from said first voltage level to said second voltage level;
• said first transistor of an ith power supply detecting unit in said chain is turned on in response to said ready signal of an (i−1)th power supply detecting unit indicating that said supply voltage level has reached said predetermined voltage level, where 2≦i≦N;
• and
• said ready signal of an Nth power supply detecting unit in said chain indicates to said processing circuit whether said supply voltage level has reached said predetermined voltage level.

A processing apparatus comprising:

• a processing circuit;
• a power supply rail for supplying a supply voltage level to said processing circuit;
• power control circuitry for switching said supply voltage level from a first voltage level to a second voltage level;
• and
• power supply detection circuitry, coupled to a power supply rail for a processing circuit, comprising at least one power supply detecting unit for detecting whether, when switching a supply voltage level of said power supply rail from a first voltage level to a second voltage level, said supply voltage level has reached a predetermined voltage level, said power supply detecting unit comprising:
• a signal output for outputting a ready signal indicating whether said supply voltage level has reached said predetermined voltage level;
• a signal node coupled to said signal output, said signal output outputting said ready signal in dependence on a signal node voltage level at said signal node;
• a first transistor coupled to said power supply rail and said signal node;
• and
• a second transistor coupled to said signal node and an external voltage supply having an external voltage level;
• wherein:
• said first transistor and said second transistor are configured, when switching said supply voltage level from said first voltage level to said second voltage level, to compete with said first transistor pulling said signal node voltage level towards said supply voltage level and said second transistor pulling said signal node voltage level towards said external voltage level, said first transistor being configured to overcome said second transistor when said supply voltage level reaches said predetermined voltage level;
• and
• said signal output is configured to output said ready signal in dependence on when said first transistor overcomes said second transistor;
• and
• a first processing circuit and a second processing circuit, said first processing circuit and said second processing circuit each having a corresponding power supply rail and power control circuit, at least said first processing circuit having a corresponding power supply detection circuitry;
• wherein switching of said supply voltage level for said second processing circuit from said first voltage level to said second voltage level is initiated in response to said power supply detection circuitry for said first processing circuit outputting said ready signal indicating that said supply voltage level for said first processing circuit has reached said predetermined voltage level.