Duty cycle controller with calibration circuit
First Claim
1. A duty-cycle adjustor comprising:
- an integrator for integrating a charging current to generate a ramp voltage having a cycle controlled by an input clock;
a switched current-source array for generating the charging current, wherein a magnitude of the charging current is selectable by first configuration signals;
a comparator that compares the ramp voltage to a threshold voltage, the comparator driving an output clock to a first logic state when the ramp voltage is above the threshold voltage, the comparator driving an output clock to a second logic state that is a logical opposite of the first logic state when the ramp voltage is below the threshold voltage;
a tunable voltage reference that generates a reference voltage, wherein a magnitude of the reference voltage is selectable by second configuration signals;
a tunable voltage divider that divides the reference voltage by a divisor to generate the threshold voltage, wherein the divisor is determined by third configuration signals;
a zero duty onset detector that examines the output clock and signals a zero duty onset condition when the output clock stops pulsing between the first logic state and the second logic state; and
a calibration controller that performs calibration by adjusting the first and second configuration signals until the zero duty onset detector signals the zero duty onset condition, the calibration controller storing the first configuration signals and the second configuration signals as a stored configuration when the zero duty onset condition is signaled;
wherein after calibration is completed, the calibration controller sends the first configuration signals from the stored configuration to the switched current-source array and sends the second configuration signals from the stored configuration to the tunable voltage reference,whereby the charging current and the reference voltage are adjusted by calibration detecting the zero duty onset condition.
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Abstract
An integrator in a duty-cycle adjustment circuit has an adjustable charging current provided by a switched current-source array in response to configuration signals from the calibration logic. The integrator'"'"'s ramp voltage is compared to a threshold voltage by a comparator to generate an output clock. A tunable voltage reference generates a reference voltage that can be tuned by configuration signals from the calibration logic. The reference voltage is divided by a tunable voltage divider, which selects different fractions of the reference voltage for use as the threshold voltage. During calibration, calibration logic repeatedly raises the reference voltage or reduces the charging current from the switched current-source array until a peak voltage of the ramp voltage equals the reference voltage, when a zero duty onset detector detects that the output clock has stopped pulsing. The configuration signals at the zero duty onset condition are stored and used for normal operation.
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Citations
20 Claims
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1. A duty-cycle adjustor comprising:
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an integrator for integrating a charging current to generate a ramp voltage having a cycle controlled by an input clock; a switched current-source array for generating the charging current, wherein a magnitude of the charging current is selectable by first configuration signals; a comparator that compares the ramp voltage to a threshold voltage, the comparator driving an output clock to a first logic state when the ramp voltage is above the threshold voltage, the comparator driving an output clock to a second logic state that is a logical opposite of the first logic state when the ramp voltage is below the threshold voltage; a tunable voltage reference that generates a reference voltage, wherein a magnitude of the reference voltage is selectable by second configuration signals; a tunable voltage divider that divides the reference voltage by a divisor to generate the threshold voltage, wherein the divisor is determined by third configuration signals; a zero duty onset detector that examines the output clock and signals a zero duty onset condition when the output clock stops pulsing between the first logic state and the second logic state; and a calibration controller that performs calibration by adjusting the first and second configuration signals until the zero duty onset detector signals the zero duty onset condition, the calibration controller storing the first configuration signals and the second configuration signals as a stored configuration when the zero duty onset condition is signaled; wherein after calibration is completed, the calibration controller sends the first configuration signals from the stored configuration to the switched current-source array and sends the second configuration signals from the stored configuration to the tunable voltage reference, whereby the charging current and the reference voltage are adjusted by calibration detecting the zero duty onset condition. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method for calibrating a duty-cycle controller comprising:
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configuring a tunable voltage reference to generate a reference voltage having a minimum value; configuring a tunable voltage divider to pass the reference voltage through to a threshold voltage; configuring a switched current-source array to generate a charging current having a maximum value; operating an integrator to charge a capacitor using the charging current and to discharge the capacitor in response to an input clock to generate a ramp voltage; comparing the ramp voltage to the threshold voltage and driving an output clock to a first state when the ramp voltage is less than the threshold voltage, and driving the output clock to a second state when the ramp voltage is less than the threshold voltage; monitoring the output clock and signaling a zero duty onset condition when the output clock stops pulsing between the first state and the second state; when the zero duty onset condition is not yet signaled, successively reducing the charging current until a minimum charging current is reached; when the zero duty onset condition is not yet signaled and the minimum charging current is reached, successively increasing the reference voltage; when the zero duty onset condition is not yet signaled and the minimum charging current is reached, and a maximum of the reference voltage is reached, signaling a calibration limit; when the zero duty onset condition is signaled, storing a configuration setting of the switched current-source array and of the tunable voltage reference and using this configuration setting for operation of the duty-cycle controller to generate the output clock; and when the zero duty onset condition is signaled, applying a target configuration setting for the tunable voltage divider that causes the tunable voltage divider to divide the reference voltage by a divisor K to generate the threshold voltage, wherein K is more than one, wherein the target configuration setting determines a target duty cycle for the output clock. - View Dependent Claims (15, 16, 17)
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18. A selectable duty-cycle clock generator comprising:
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a voltage ramp generator that generates a ramp voltage having a triangular waveform that is synchronized to an input clock; a signal strength adjuster that adjusts a peak voltage of the ramp voltage in response to first configuration signals; a comparator that compares the ramp voltage to a threshold voltage to generate an output clock; a tunable voltage reference that generates a reference voltage determined by second configuration signals; a tunable voltage divider that dividers the reference voltage to generate the threshold voltage, the tunable voltage divider dividing the reference voltage by an amount determined by third configuration signals; a zero duty detector for detecting a calibration endpoint when the output clock has a zero duty cycle wherein pulses of the output clock have an insufficient pulse width to meet timing requirements; and calibration logic that receives a target duty cycle and drives the third configuration signals with a value causing the output clock to have the target duty cycle during a normal operation mode; wherein the calibration logic further comprising means for performing a calibration routine to generate a calibrated set of the first and second calibration signals that cause the zero duty cycle to detect the calibration endpoint; wherein the calibration logic applies the calibrated set of the first calibration signals to the signal strength adjuster and applies the calibrated set of the second calibration signals to the tunable voltage reference during the normal operation mode; whereby the target duty cycle is calibrated. - View Dependent Claims (19, 20)
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Specification