US5646518A — PTAT current source

Claim 1

Independent Claim 161 words

A current source that supplies a current substantially proportional to absolute temperature for use in an integrated circuit comprising: a first current path and a second current path driven by a fixed current source; said current paths being coupled so as to provide a first current and a second current flowing through the respective current paths at least during circuit operation, said first current and said second current being in a substantially predetermined direct proportion; and an operational amplifier including respective input terminals respectively coupled to said first current path and said second current path, said operational amplifier being coupled in a feedback configuration so as to maintain substantially equal first and second voltages between a first substantially predetermined point and a second substantially predetermined point respectively located along said first current path and said second current path; the respective first and second currents being related to the respective first and second voltages substantially in accordance with a junction diode equation.

Claim 2

Dependent Claim 161 words

A current source that supplies a current substantially proportional to absolute temperature for use in an integrated circuit comprising: a first current path and a second current path driven by a fixed current source; said current paths being coupled so as to provide a first current and a second current flowing through the respective current paths at least during circuit operation, said first current and said second current being in a substantially predetermined direct proportion; and an operational amplifier including respective input terminals respectively coupled to said first current path and said second current path, said operational amplifier being coupled in a feedback configuration so as to maintain substantially equal first and second voltages between a first substantially predetermined point and a second substantially predetermined point respectively located along said first current path and said second current path; the respective first and second currents being related to the respective first and second voltages substantially in accordance with a junction diode equation.

Claim 3

Dependent Claim 35 words

The current source of claim 1, wherein a current mirror is coupled to the respective current paths so as to substantially maintain said first current and said second current in a substantially predetermined direct proportion.

Claim 4

Dependent Claim 19 words

The current source of claim 2, wherein said current mirror is formed from at least two standard MOS devices.

Claim 5

Dependent Claim 25 words

The current source of claim 3, wherein said integrated circuit comprises an integrated circuit processed in accordance with a standard MOS integrated circuit fabrication process.

Claim 6

Dependent Claim 19 words

The current source of claim 2, wherein the respective current paths are coupled to a low voltage power supply.

Claim 7

Dependent Claim 19 words

The current source of claim 5, wherein said low voltage power supply comprises a power supply below 2 volts.

Claim 8

Dependent Claim 63 words

The current source of claim 2, wherein a first bipolar transistor and a second bipolar transistor are respectively coupled to said first current path and said second current path in a configuration so that said first current and said second current through the respective current paths are related to the respective first and second voltages substantially in accordance with the junction diode equation.

Claim 9

Dependent Claim 34 words

The current source of claim 2, wherein said current source is coupled in a circuit configuration further including a load element and a bipolar transistor so as to provide a bandgap voltage reference generator.

Claim 10

Dependent Claim 17 words

The current source of claim 2, and further comprising a start-up circuit coupled to said current source.

Claim 11

Dependent Claim 15 words

The current source of claim 2, wherein said operational amplifier comprises a folded-cascode operational amplifier.

Claim 12

Dependent Claim 55 words

The current source of claim 10, wherein the current source constitutes a PTAT current source, said operational amplifier being adapted to be powered by an external current source, the external current source being adapted to supply current to said operational amplifier developed at least in part from the current supplied by said PTAT current source.

Claim 13

Dependent Claim 205 words

A current source supplying a current substantially proportional to absolute temperature, said current source comprising: a first current path and a second current path; said first path including a first semiconductor device; said second path including a second semiconductor device; said first current path and said second current path being coupled to a current mirror so as to respectively maintain a first current in said first current path and a second current in said second current path, said currents being in a substantially predetermined direct proportion; and an operational amplifier including two input terminals respectively coupled to a first predetermined point and a second predetermined point respectively located along said first current path and said second current path between said current mirror and said semiconductor devices, said operational amplifier being coupled in a feedback configuration so as to maintain substantially equal voltages between said first and second predetermined points, wherein said first semiconductor device is a first bipolar transistor coupled by an emitter through a resistor to said operational amplifier and said second semiconductor device is a second bipolar transistor coupled by an emitter to said operational amplifier, wherein bases and collectors of said first bipolar transistor and said second bipolar transistor are mutually connected.

Claim 14

Dependent Claim 205 words

A current source supplying a current substantially proportional to absolute temperature, said current source comprising: a first current path and a second current path; said first path including a first semiconductor device; said second path including a second semiconductor device; said first current path and said second current path being coupled to a current mirror so as to respectively maintain a first current in said first current path and a second current in said second current path, said currents being in a substantially predetermined direct proportion; and an operational amplifier including two input terminals respectively coupled to a first predetermined point and a second predetermined point respectively located along said first current path and said second current path between said current mirror and said semiconductor devices, said operational amplifier being coupled in a feedback configuration so as to maintain substantially equal voltages between said first and second predetermined points, wherein said first semiconductor device is a first bipolar transistor coupled by an emitter through a resistor to said operational amplifier and said second semiconductor device is a second bipolar transistor coupled by an emitter to said operational amplifier, wherein bases and collectors of said first bipolar transistor and said second bipolar transistor are mutually connected.

Claim 15

Dependent Claim 56 words

The current source of claim 12, wherein the last-recited current source constitutes a PTAT current source, said operational amplifier being adapted to be powered by an external current source, the external current source being adapted to supply current to said operational amplifier developed at least in part from the current supplied by said PTAT current source.

Claim 16

Independent Claim 183 words

A method of supplying a current substantially proportional to absolute temperature on an integrated circuit; said integrated circuit including a first current path and a second current path; said current paths being coupled to a current mirror so as to respectively maintain first and second currents through the respective current paths at least during integrated circuit operation, said first current and said second current being in a substantially predetermined direct proportion; said first current path and said second current path respectively having a substantially predetermined point located along the respective current paths, each of the predetermined points having a voltage; in each current path, the voltage at the predetermined point along the current path being related to the current through the current path substantially in accordance with a junction diode equation; said method comprising the steps of: driving said first current path and said second current path using a fixed current source; comparing the voltages at the respective predetermined points along the respective current paths; and applying a voltage to the respective paths, at least in part in accordance with the voltage comparison.

Claim 17

Independent Claim 183 words

A method of supplying a current substantially proportional to absolute temperature on an integrated circuit; said integrated circuit including a first current path and a second current path; said current paths being coupled to a current mirror so as to respectively maintain first and second currents through the respective current paths at least during integrated circuit operation, said first current and said second current being in a substantially predetermined direct proportion; said first current path and said second current path respectively having a substantially predetermined point located along the respective current paths, each of the predetermined points having a voltage; in each current path, the voltage at the predetermined point along the current path being related to the current through the current path substantially in accordance with a junction diode equation; said method comprising the steps of: driving said first current path and said second current path using a fixed current source; comparing the voltages at the respective predetermined points along the respective current paths; and applying a voltage to the respective paths, at least in part in accordance with the voltage comparison.

Claim 18

Dependent Claim 55 words

The method of claim 14, wherein the step of comparing the voltages at the respective predetermined points along the respective current paths comprises applying the voltages to the input terminals of an operational amplifier; and the step of applying a voltage comprises applying the output voltage of said operational amplifier to the respective current paths.

Claim 19

Dependent Claim 67 words

The current source of claim 1, wherein the junction diode equation determines a relationship between a current through a semiconductor device and a voltage across the device that satisfies: ##EQU5## where I is the device current, V is the device voltage, I o is a reverse saturation current, V T is a thermal voltage, and n is a constant related to properties of the semiconductor material employed.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	2000-07-07	2001-01-06	2001-07-08	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	2004-07-07	2005-01-06	2005-07-08	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2008-07-07	2009-01-06	2009-07-08	$7700.00	Window Closed / Lapsed

PTAT current source

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