Integrated relaxation oscillator with improved sensitivity to component variation due to process-shift
First Claim
1. An oscillator with improved sensitivity to component variation due to process shift, comprising:
- a first comparator circuit and a second comparator circuit;
a charging-discharging circuit coupled to a first input of the first comparator circuit and to a first input of the second comparator circuit;
a resistor string coupled to a second input of the first comparator circuit and to a second input of the second comparator circuit;
a latch configured to combine an output of the first comparator circuit and an output of the second comparator circuit;
wherein the resistor string is operable to maintain a first reference voltage at the second input of the first comparator circuit and a second reference voltage at the second input of the second comparator circuit;
wherein the first reference voltage is substantially higher than the second reference voltage;
wherein an output of the latch is coupled to the charging-discharging circuit, forming a feedback loop;
wherein the output of the first comparator circuit is operable to change states when the first input of the first comparator circuit reaches a voltage level substantially commensurate with the first reference voltage;
wherein the output of the second comparator circuit is operable to change states when the first input of the second comparator circuit reaches a voltage level substantially commensurate with the second reference voltage;
wherein the charging-discharging circuit is operable to charge the first input of the first comparator circuit and the first input of the second comparator circuit to a voltage level substantially commensurate with the first reference voltage;
wherein the charging-discharging circuit is operable to discharge the first input of the first comparator circuit and the first input of the second comparator circuit to a voltage level substantially commensurate with the second reference voltage; and
wherein the resistor string comprises at least two different structure types.
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Accused Products
Abstract
A system and method for designing an integrated relaxation oscillator that exhibits reduced change in the frequency of oscillation caused by process variation. Improved sensitivity to component variation due to process shift is achieved through using more than one structure type when implementing the resistors affecting the RC time constant and threshold (trip point) voltages of the oscillator. Structure types are related to the fabrication process and for a CMOS process include, but are not limited to n-diffusion, p-diffusion, n-well, p-well, pinched n-well, pinched p-well, poly-silicon and metal. Each structure type exhibits statistically independent process variations, allowing for application of Lyapunov'"'"'s extension of the Central Limit Theorem for statistically uncorrelated events to desensitize the effect from different possible causes. Thus, improvement in the performance of the oscillator may be achieved with a reduced trim requirement and without using external precision resistors.
53 Citations
20 Claims
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1. An oscillator with improved sensitivity to component variation due to process shift, comprising:
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a first comparator circuit and a second comparator circuit;
a charging-discharging circuit coupled to a first input of the first comparator circuit and to a first input of the second comparator circuit;
a resistor string coupled to a second input of the first comparator circuit and to a second input of the second comparator circuit;
a latch configured to combine an output of the first comparator circuit and an output of the second comparator circuit;
wherein the resistor string is operable to maintain a first reference voltage at the second input of the first comparator circuit and a second reference voltage at the second input of the second comparator circuit;
wherein the first reference voltage is substantially higher than the second reference voltage;
wherein an output of the latch is coupled to the charging-discharging circuit, forming a feedback loop;
wherein the output of the first comparator circuit is operable to change states when the first input of the first comparator circuit reaches a voltage level substantially commensurate with the first reference voltage;
wherein the output of the second comparator circuit is operable to change states when the first input of the second comparator circuit reaches a voltage level substantially commensurate with the second reference voltage;
wherein the charging-discharging circuit is operable to charge the first input of the first comparator circuit and the first input of the second comparator circuit to a voltage level substantially commensurate with the first reference voltage;
wherein the charging-discharging circuit is operable to discharge the first input of the first comparator circuit and the first input of the second comparator circuit to a voltage level substantially commensurate with the second reference voltage; and
wherein the resistor string comprises at least two different structure types. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. An oscillator with improved sensitivity to component variation due to process shift, comprising:
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a first comparator circuit and a second comparator circuit;
a resistor string coupled to a second input of the first comparator circuit and to a second input of the second comparator circuit;
a latch configured to combine an output of the first comparator circuit and an output of the second comparator circuit;
a resistance coupling an output of the latch to a first input of the first comparator circuit and to a first input of the second comparator circuit;
a capacitance coupling a common ground to the first input of the first comparator circuit and to the first input of the second comparator circuit;
wherein the resistor string is operable to maintain a first reference voltage at the second input of the first comparator circuit and a second reference voltage at the second input of the second comparator circuit;
wherein the first reference voltage is substantially higher than the second reference voltage;
wherein the output of the first comparator circuit is operable to change states when the first input of the first comparator circuit reaches a voltage level substantially commensurate with the first reference voltage;
wherein the output of the second comparator circuit is operable to change states when the first input of the second comparator circuit reaches a voltage level substantially commensurate with the second reference voltage; and
wherein the resistance comprises at least two different structure types. - View Dependent Claims (11, 12, 13, 14, 15)
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16. A method for implementing an integrated oscillator with improved sensitivity to component variation due to process shift, the method comprising:
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forming a first resistance of a first structure type;
forming a second resistance of a second structure type, wherein the second structure type is different from the first structure type;
forming a third resistance, wherein the third resistance comprises a first resistor of the first structure type and a second resistor of the second structure type;
coupling a supply voltage to a first input of a first comparator circuit through the first resistance;
coupling the first input of the first comparator circuit to a first input of a second comparator circuit through the second resistance;
coupling the first input of the second comparator circuit to a common ground through the third resistance;
coupling an output of the first comparator circuit and an output of the second comparator circuit to a latch;
coupling an output of the latch to a second input of the first comparator circuit and to a second input of the second comparator circuit through a charge-discharge circuit; and
providing the output of the latch as output of the integrated oscillator. - View Dependent Claims (17, 18, 19, 20)
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Specification