Programmable current source with optimized compliance region for efficient backlighting in portable applications
First Claim
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1. A programmable current source circuit comprising:
- a digital-to-analog (DAC) current source structured to provide an incrementally adjustable output current signal to an external circuit;
a programmable reference current source connected to the DAC current source to adjust a compliance factor of the DAC current source;
a digital selector in communication with a control circuit to receive a digital adjustment code from the external control circuit and decode the digital adjustment code to form a decoded output current magnitude signal to select an amplitude for the incrementally adjustable output current signal; and
an adjustment code modification circuit is connected to the digital selector to receive the decoded output current magnitude signal to determine if a magnitude of the incrementally adjustable output current signal is greater or less than an activation compliance level for adjusting a reference current of the programmable reference current source to adjust the compliance factor of the DAC current source and to modify the decoded output current magnitude signal for a desired incrementally adjustable output current signal.
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Abstract
A programmable current source programmable current source circuit has DAC current source providing an incrementally programmable current levels. A programmable reference current source adjusts a compliance factor of the DAC current source. An input adjustment code indicating an output current amplitude is adjusted by a adjustment code modification circuit when the output current is less than the activation compliance level and generates a signal to set the reference current to a lower level to adjust the compliance factor of the DAC current source to a lower level to decrease power dissipation in the programmable current source at lower current levels.
10 Citations
16 Claims
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1. A programmable current source circuit comprising:
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a digital-to-analog (DAC) current source structured to provide an incrementally adjustable output current signal to an external circuit; a programmable reference current source connected to the DAC current source to adjust a compliance factor of the DAC current source; a digital selector in communication with a control circuit to receive a digital adjustment code from the external control circuit and decode the digital adjustment code to form a decoded output current magnitude signal to select an amplitude for the incrementally adjustable output current signal; and an adjustment code modification circuit is connected to the digital selector to receive the decoded output current magnitude signal to determine if a magnitude of the incrementally adjustable output current signal is greater or less than an activation compliance level for adjusting a reference current of the programmable reference current source to adjust the compliance factor of the DAC current source and to modify the decoded output current magnitude signal for a desired incrementally adjustable output current signal. - View Dependent Claims (2, 3, 4, 5)
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6. An electronic apparatus comprising:
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at least one electronic device requiring a current with programmable current levels; and a programmable current source circuit for providing the programmable current levels to the at least one electronic device comprising; a digital-to-analog (DAC) current source structured to provide an incrementally programmable current levels to at least one electronic device, a programmable reference current source connected to the DAC current source to adjust a compliance factor of the DAC current source, a digital selector in communication with a control circuit to receive a digital adjustment code from the external control circuit and decode the digital adjustment code for form a decoded output current magnitude signal to select an amplitude for the incrementally programmable current levels, and an adjustment code modification circuit is connected to the digital selector to receive the decoded output current magnitude signal to determine if a magnitude of the incrementally programmable current levels is greater or less than an activation compliance level for adjusting a reference current of the programmable reference current source to adjust the compliance factor of the DAC current source and to modify the decoded output current magnitude signal for a desired incrementally programmable current levels. - View Dependent Claims (7, 8, 9, 10)
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11. A Liquid crystal display (LCD) display comprising:
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plurality of serially connected LED'"'"'s for backlighting the LCD display requiring a current with programmable current levels to adjust brightness of the LED'"'"'s; and a programmable current source circuit connected to the plurality of serially connected LED'"'"'s to provide the programmable current levels comprising; a digital-to-analog (DAC) current source structured to provide incrementally programmable current levels to the plurality of serially connected LED'"'"'s, a programmable reference current source connected to the DAC current source to adjust a compliance factor of the DAC current source, a digital selector in communication with a control circuit to receive a digital adjustment code from the external control circuit and decode the digital adjustment code for form a decoded output current magnitude signal to select an amplitude for the incrementally programmable current levels, and an adjustment code modification circuit is connected to the digital selector to receive the decoded output current magnitude signal to determine if a magnitude of the incrementally programmable current levels is greater or less than an activation compliance level for adjusting a reference current of the programmable reference current source to adjust the compliance factor of the DAC current source and to modify the decoded output current magnitude signal for a desired incrementally programmable current levels. - View Dependent Claims (12, 13, 14)
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15. A method for adjusting a programmable current source to have a very low compliance factor and a wide range of source current, comprising the steps of:
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providing a programmable current source having a DAC current source connected to a programmable reference current source; examining amplitude current adjustment code to determine if an output current signal of the DAC current source is to be set to an amplitude greater or less than a compliance activation level; setting the programmable reference current source to be a first reference current level that allows the output current level to have a wide range of selectable upper current levels and applying a decoded amplitude adjustment code to the DAC current source, when the amplitude adjustment code is greater than the compliance activation level; and setting the programmable reference current source to be a second reference current level that allows the programmable current source to have a low compliance level and modifying a decoded amplitude adjustment code such that the output current signal have a magnitude indicated by the amplitude adjustment code, when the amplitude adjustment code is less than the compliance activation level.
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16. An apparatus for adjusting a programmable current source to have a very low compliance factor and a wide range of source current, comprising the steps of:
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means for providing a programmable current source having a DAC current source connected to the programmable reference current source; means for examining amplitude current adjustment code to determine if an output current signal of the DAC current source is to be set to an amplitude greater or less than a compliance activation level; means for setting the programmable reference current source to be a first reference current level that allows the output current level to have a wide range of selectable upper current levels and applying a decoded amplitude adjustment code to the DAC current source, when the amplitude adjustment code is greater than the compliance activation level; and means for setting the programmable reference current source to be a second reference current level that allows the programmable current source to have a low compliance level and modifying a decoded amplitude adjustment code such that the output current signal have a magnitude indicated by the amplitude adjustment code, when the amplitude adjustment code is less than the compliance activation level.
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Specification