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US 5,828,329 AGranted
Adjustable temperature coefficient current reference
Assignee3Com Corporation
InventorLawrence M. Burns
Life of this patent
Estimating the term…
Abstract
A current reference combines proportional to absolute temperature and complementary to absolute temperature current sources to produce a current reference that is relatively immune to power supply variations and features a temperature coefficient which may be adjusted to yield a positive, negative or zero tempco. In its preferred embodiment, the new current reference may be advantageously employed within an analog to digital converter (ADC) to yield equal quantization values in spite of variations in the ADC's supply voltage and temperature. Additionally, the tempco may be adjusted to permit the ADC's quantization valued to "track" variations in circuitry which produce the analog signals converted by the ADC.
Claims14
A current reference circuit, comprising:
- a proportional to absolute temperature (PTAT) current source having at least one resistor, said PTAT current source producing a PTAT current output which is a function of said resistor, and
- a complementary to absolute temperature (CTAT) current source which produces a CTAT current output in response to a constant current input, said CTAT current source (a) connected to receive a PTAT current input from said PTAT current source, (b) having at least one resistor, and (c) connected to produce a reference output current which can have a zero, negative or positive temperature coefficient, depending upon the values of said PTAT and CTAT current source resistors.
An analog to digital converter (ADC), comprising:
- a differential voltage input for receiving analog signals which are to be converted into digital form,
- a differential resistor ladder connected to receive differential voltage signals from said input, said ladder comprising at least one leg of resistors with taps at the junctions of said resistors, and
- a current reference connected to said ladder to produce a voltage across at least one leg of the ladder which is substantially equal to the input range of the ADC, and to produce a voltage across each resistor within the leg equal to one of the ADC's quantization levels, said current reference comprising:
- a proportional to absolute temperature (PTAT) current source having at lease one resistor, said PTAT current source producing a PTAT current output which is a function of said resistor, and
- a complementary to absolute temperature (CTAT) current source which produces a CTAT current output in response to a constant current input, said CTAT current source (a) connected to receive a PTAT current input from said PTAT current source, (b) having at least one resistor, and (c) connected to produce a reference output current which can have a zero, negative or positive temperature coefficient, depending upon the values of said PTAT and CTAT current source resistors.
2 more elements
A received signal strength indicator, comprising:
- an interface circuit including an input low pass filter amplifier connectable to receive a differential input current representative of an amplitude envelope of an RF signal and to produce a low pass filtered differential voltage output, and
- an analog to digital converter (ADC) connected to convert said differential voltage output into digital form, said ADC including a current reference connected to determine its quantization levels, said ADC comprising:
- differential voltage inputs connected to receive said differential voltage output,
- a differential resistor ladder connected to receive differential voltage signals from said input, said ladder comprising at least one leg of resistors with taps at the junctions of said resistors, and
- a current reference connected to said ladder to produce a voltage across at least one leg of the ladder, said voltage being substantially equal to the input range of the ADC, and to produce a voltage across each resistor within the leg equal to one of the ADC's quantization levels, said current reference comprising:
- a proportional to absolute temperature (PTAT) current source having at lease one resistor, said PTAT current source producing a PTAT current output which is a function of said resistor, and
- a complementary to absolute temperature (CTAT) current source which produces a CTAT current output in response to a constant current input, said CTAT current source (a) connected to receive a PTAT current input from said PTAT current source, (b) having at least one resistor, and (c) connected to produce a reference output current which can have a zero, negative or positive temperature coefficient, depending upon the values of said PTAT and CTAT current source resistors.
4 more elements
A radio frequency (RF) receiver, comprising:
- an antenna connected to receive RF signals,
- a bandpass filter connected to filter said received signals,
- an amplifier connected to amplify said RF signals and to produce a differential current output signal representative of said RF signals, and
- a received signal strength indicator which comprises:
- an interface circuit including an input low pass filter amplifier connectable to receive a differential input current representative of a demodulated RF signal and to produce a low pass filtered differential voltage output, and
- an analog to digital converter (ADC) having differential voltage inputs connected to receive said differential voltage output, said ADC further comprising:
- a differential resistor ladder connected to receive differential voltage signals from said input, said ladder comprising at least one leg of resistors with taps at the junctions of said resistors, and
- a current reference connected to said ladder to produce a voltage across at least one leg of the ladder which is substantially equal to the input range of the ADC, and to produce a voltage across each resistor within the leg equal to one of the ADC's quantization levels, said current reference comprising:
- a proportional to absolute temperature (PTAT) current source having at lease one resistor, said PTAT current source producing a PTAT current output which is a function of said resistor, and
- a complementary to absolute temperature (CTAT) current source which produces a CTAT current output in response to a constant current input, said CTAT current source (a) connected to receive a PTAT current input from said PTAT current source, (b) having at least one resistor, and (c) connected to produce a reference output current which can have a zero, negative or positive temperature coefficient, depending upon the values of said PTAT and CTAT current source resistors.
7 more elements
A current reference circuit, comprising:
- a proportional to absolute temperature (PTAT) current source comprising:
- a first pair of transistors connected in a current mirror circuit,
- a second pair of transistors that are cross-coupled to each other and connected to receive currents from respective transistors of said first pair, said second pair of transistors have current outputs that are connected together to yield a combined PTAT current,
- a first resistor connected between respective transistors of said first and second transistor pairs, and
- a second resistor connected between one of the transistors of said second pair and the connection between said second pair's current outputs, and
- a complementary to absolute temperature (CTAT) current source, comprising:
- an output transistor connected to be biased in common with said first pair of transistors, and to produce a reference current output,
- an impedance circuit connected to receive said reference current output,
- an input transistor connected to receive said combined PTAT current, to produce a current output, and to be biased by said impedance, and
- a third resistor connected to receive the current output flow from said output transistor,
- the temperature coefficient of said reference current output depending upon the resistance values of said first, second and third resistors.
8 more elements
Dependencies are inferred from the claim text.