Integrated circuit power-on control and programmable comparator

An integrated circuit comprising:

• power switching means coupled to a power source having a source voltage level and to a virtual power rail;
• logic means coupled to said virtual power rail to draw power therefrom;
• and
• a power-on control means coupled to said power switching means for controlling said power switching circuitry to operate in a plurality of modes include a pre-charge mode in which said virtual power rail is connected to said power source via a weak path during pre-charging of said virtual power rail and an active mode in which said virtual power rail is connected to said power source via a strong path during active operation of said logic means;
• wherein
• said power-on control means comprises:
• comparator means for outputting a sense signal in response to a voltage on said virtual power rail passing a reference voltage, while being driven toward said source voltage by conduction through said power switching means during said pre-charge mode;
• and
• latch means for latching a trigger signal coupled to said power switching means in response to said sense signal to switch said power switching circuitry to said active mode.

A method of controlling power-on operation in an integrated circuit having power-switching circuitry coupled to a power source having a source voltage level and to a virtual power rail and logic circuitry coupled to said virtual power rail to draw power therefrom, said method comprising the steps of:

• driving a voltage on said virtual power rail toward a reference voltage by conduction through a weak path through said power-switching circuitry during a pre-charge mode;
• comparing a voltage on said virtual power rail with a reference voltage to detect said voltage on said virtual power rail passing said source voltage;
• in response to said voltage on said second power rail passing said source voltage, outputting a sense signal;
• and
• in response to said sense signal, latching a trigger signal coupled to said power switching circuitry to switch said power switching circuitry to an active mode in which said virtual power rail is connected to said power source via a strong path during active operation of said logic circuitry.

A method of comparing a variable voltage with a selected one of a plurality of predetermined voltages within an integrated circuit, said selected one of said plurality of predetermined voltages being selected in response to a reference-setting signal, said method comprising the steps of:

• removing charge from a node with at least one discharge-transistor at a rate controlled by a difference between a fixed voltage and said variable voltage;
• and
• supplying charge to said node with a plurality of charge-transistors each capable of supplying charge at a maximum saturated rate, and
• controlling with said reference-setting signal how many of said plurality of charge-transistor are active to supply charge to said node in opposition to said at least one discharge-transistor removing charge from said node and accordingly by how much said variable voltage must differ from said fixed voltage in order to discharge said node;
• and
• generating, in response to said reference-setting signal, a thermometer coded signal to control how many of said charge-transistors are active.

A method of comparing a variable voltage with a selected one of a plurality of predetermined voltages within an integrated circuit, said selected one of said plurality of predetermined voltages being selected in response to a reference-setting signal, said method comprising the steps of:

• supplying charge to a node with at least one charge-transistor at a rate controlled by a difference between a fixed voltage and said variable voltage;
• and
• removing charge from said node with a plurality of discharge-transistors each capable of removing charge at a maximum saturated rate, and
• controlling with said reference-setting signal how many of said plurality of discharge-transistor are active to remove charge from said node in opposition to said at least one charge-transistor supplying charge from said node and accordingly by how much said variable voltage must differ from said fixed voltage in order to discharge said node;
• and
• generating, in response to said reference-setting signal, a thermometer coded signal to control how many of said discharge-transistors are active.