Analog-to-digital converter with sigma-delta duty cycle encoded output
First Claim
1. An analog-to-digital converter (ADC), comprising:
- a clock having a frequency output that can vary with temperature, anda modulating circuit connected to receive an input analog signal and to operate in response to said clock output, said modulating circuit producing a digital output with a duty cycle that corresponds to an input analog signal generally independent of the clock frequency,said modulating circuit comprising a sigma-delta modulator which receives said input analog signal, and an output circuit which responds to said sigma-delta modulator and to said clock output to produce said digital output, wherein said clock output and an output signal from said sigma-delta modulator are selectively applied one-at-a-time as inputs to said output circuit.
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Accused Products
Abstract
An analog-to-digital converter employs a sigma-delta modulator that produces a pulsed output with an average duty cycle that varies with an analog input to the modulator. A counter averages the modulator'"'"'s output duty cycle, and feeds the averaged information onto a one-line transmission circuit for delivery to a remote location. Both the sigma-delta modulator and the counter are synchronized to the same local clock, so that the counter'"'"'s duty cycle remains substantially constant even if the clock frequency varies. This allows for a simple clock configuration that can be integrated along with the sigma-delta modulator and counter on a single IC chip of reasonable size. When used for temperature sensing, the counter'"'"'s output duty cycle provides an indication of the locally sensed temperature, independent of temperature-induced variations in the clock frequency.
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Citations
16 Claims
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1. An analog-to-digital converter (ADC), comprising:
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a clock having a frequency output that can vary with temperature, and a modulating circuit connected to receive an input analog signal and to operate in response to said clock output, said modulating circuit producing a digital output with a duty cycle that corresponds to an input analog signal generally independent of the clock frequency, said modulating circuit comprising a sigma-delta modulator which receives said input analog signal, and an output circuit which responds to said sigma-delta modulator and to said clock output to produce said digital output, wherein said clock output and an output signal from said sigma-delta modulator are selectively applied one-at-a-time as inputs to said output circuit. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A circuit for converting an analog input signal to an output digital signal whose duty cycle represents said input signal, comprising:
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a two-phase clock circuit having first and second complementary outputs, a sigma-delta modulator that is connected to receive said analog input signal and is synchronized to said complementary clock outputs, and produces in response thereto an output pulsed signal whose duty cycle varies with the analog input signal, and a counter circuit having an input that is connected to receive the sigma-delta modulator output when a predetermined higher order counter bit is in one digital state, and to receive one of the clock outputs when said predetermined counter bit is in the opposite digital state, the counter producing a digital output that alternates between complementary digital states, with the duration of the counter output in one state varying as a function of the clock frequency and in the other state as a function of the duty cycle of the sigma-delta modulator output. - View Dependent Claims (11, 12, 13, 14, 15, 16)
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Specification