VBB reference for pumped substrates
AssigneeLattice Semiconductor Corporation
InventorsJames Gorecki, Ravindar Lall, Robert B. Lefferts
Life of this patent
Estimating the term…
Abstract
An embodiment of a pumped substrate system includes an oscillator, capacitive pump, comparing circuit, and a level shifter. The level shifter is coupled between the substrate and the positive input lead of the comparator and shifts the voltage level present on the substrate by a voltage Vbg. The comparator compares ground potential to the shifted substrate voltage. The oscillator, capacitive pump and comparing circuit form a negative feedback loop which operates to maintain the substrate voltage substantially equal to -Vbg. In one embodiment, the level shifter includes a band gap reference.
Claims19
A circuit implemented on a substrate having a voltage generated by a charge pump, said circuit comprising:
- a current source providing a first current that is proportional to temperature;
- and
- a level shifter coupled to said current source and said substrate, said level shifter providing
- a first voltage that is shifted from said voltage of said substrate, wherein said level shifter comprises:
- a first P-channel transistor coupled to said current source, said first P-channel transistor conducting a current substantially equal to said first current;
- a first resistive device coupled to a drain of said first P-channel transistor;
- and
- a first PNP transistor having a base and collector coupled to said substrate and an emitter coupled to said first resistive device.
A method for maintaining a voltage of a substrate at a predetermined level, said method comprising the steps of:
- providing a first voltage that is substantially equal to a sum of a base-to-emitter voltage of a transistor and a product of a thermal voltage and a constant, wherein said constant is a product of a ratio of resistances and a natural logarithm of a ratio of emitter areas;
- applying said first voltage between said substrate and a first node;
- and
- varying a charge in said substrate to maintain a voltage of said first node at a second voltage, wherein the voltage of said substrate is maintained at said predetermined level.
A structure for maintaining a voltage of a substrate at a predetermined level, said structure comprising:
- means for providing and applying a first voltage that is substantially equal to a sum of a base-emitter voltage of a transistor and a product of a thermal voltage and a constant, wherein said constant is a product of a ratio of resistances and a natural logarithm of a ratio of emitter areas;
- said first voltage being applied between said substrate and a first node;
- and
- means for varying a charge in said substrate to maintain a voltage of said first node at a second voltage, wherein the voltage of said substrate is maintained at said predetermined level.
A system for maintaining a voltage of a substrate at a predetermined voltage, said system comprising:
- an oscillator;
- a gating circuit having an input lead coupled to an output lead of said oscillator;
- a pump circuit having an input lead coupled to an output lead of said gating circuit and an output lead coupled to said substrate;
- a level shifter coupled between said substrate and a node;
- and
- a comparing circuit having a first input lead coupled to said node, a second input lead coupled to a voltage source and an output lead coupled to a control lead of said gating circuit;
- wherein said oscillator is a voltage-controlled oscillator and said comparing circuit is an amplifier, said voltage-controlled oscillator having an input lead coupled to an output lead of said amplifier.
Dependencies are inferred from the claim text.