Digital sensor with embedded reference clock
A sensor circuit and integrated circuit having the same is disclosed. In one embodiment, a sensor circuit includes first and second ring oscillators having different circuit topologies. A first counter is coupled to receive an output signal from the first ring oscillator, while a second counter is coupled to receive an output signal from the second ring oscillator. The sensor circuit further includes a local clock circuit that provides a clock signal to the first and second counters. Furthermore, the local clock circuit is coupled to provide the clock signal exclusively to circuitry within the sensor circuit, the circuitry including the first and second counters.
1. A circuit comprising:
a sensor circuit configured to sense a local voltage and a local temperature, wherein the sensor circuit includes:
a first ring oscillator having a first circuit topology;
a first counter coupled to receive a first output signal from the first ring oscillator, wherein the first counter is configured to determine a frequency of the first output signal;
a second ring oscillator having a second circuit topology different from the first circuit topology;
a second counter coupled to receive a second output signal from the second ring oscillator, wherein the second counter is configured to determine a frequency of the second output signal;
a local clock circuit configured to provide a clock signal exclusively to circuitry within the sensor circuit including the first and second counters; and
a shift register coupled to receive the clock signal from the local clock circuit, and further coupled to receive a first count value from the first counter and a second count value from the second counter.
2. The circuit as recited in claim 1 , wherein the first count value corresponds to a frequency of the first output signal and the second count value corresponds to a frequency of the second output signal.
3. The circuit as recited in claim 1 , wherein the shift register is coupled to a bus, wherein the sensor circuit is configured to convey information indicative of the frequency of the first output signal and the frequency of the second output signal to a control circuit via the bus.
4. The circuit as recited in claim 1 , wherein the local clock circuit includes a third ring oscillator.
5. The circuit as recited in claim 1 , wherein a frequency of the first output signal has a relationship to a voltage received by the sensor circuit that is different than that of the second output signal, and wherein a frequency of the first output signal has a relationship to a temperature received by the sensor circuit that is different than that of the second output signal.
6. The circuit as recited in claim 1 , wherein the first ring oscillator is implemented using a plurality of series-coupled inverters, and wherein the second ring oscillator is implemented using a plurality of series-coupled NAND gates.
7. The circuit as recited in claim 1 , wherein each of the first and second ring oscillators are characterized by first and second polynomials, respectively, wherein, during operation of an integrated circuit in which the sensor circuit is implemented, a voltage and a temperature sensed by the sensor circuit is determined by solving for a voltage and temperature using respective frequencies of the first and second output signals and the first and second polynomials.
8. The circuit as recited in claim 1 , wherein the sensor circuit is implemented within a functional circuit block of an integrated circuit, wherein each of the first and second ring oscillators are coupled to receive a supply voltage that is received by circuitry of the functional circuit block.
9. An integrated circuit comprising:
a plurality of functional circuit blocks each including functional circuitry; and
a plurality of sensors, wherein each of the plurality of functional circuit blocks includes at least one of the plurality of sensors implemented therein, and wherein each of the plurality of sensors includes:
a first ring oscillator having a first circuit topology;
a first counter coupled to receive a first output signal from the first ring oscillator;
a second ring oscillator having a second circuit topology different from the first circuit topology;
a second counter coupled to receive a second output signal from the second ring oscillator;
a local clock circuit configured to provide a clock signal exclusively to circuitry within its respective one of the plurality of sensors, the circuitry including the first and second counters;
a shift register coupled to receive a first count value from the first counter and a second count value from the second counter, wherein the shift register is coupled to receive the clock signal from the local clock circuit.
10. The integrated circuit as recited in claim 9 , wherein the first count value corresponds to a frequency of the first output signal and the second count value corresponds to a frequency of the second output signal, and wherein the integrated circuit further includes a control circuit and a bus coupled to both the control circuit and the shift register, wherein the sensor circuit is configured to convey information indicative of the frequency of the first output signal and the frequency of the second output signal from the shift register to the control circuit via the bus.
11. The integrated circuit as recited in claim 9 , wherein the local clock circuit in each of the plurality of sensors includes a third ring oscillator.
12. The integrated circuit as recited in claim 9 , wherein a frequency of the first output signal has a relationship to a voltage received by the sensor circuit that is different than a frequency of the second output signal, and wherein the frequency of the second output signal has a relationship to temperature of the sensor circuit that is different than the frequency of the first output signal.
13. The integrated circuit as recited in claim 9 , wherein the first ring oscillator is implemented using a plurality of series-coupled inverters, and wherein the second ring oscillator is implemented using a plurality of series-coupled NAND gates.
14. The integrated circuit as recited in claim 9 , wherein each of the first and second ring oscillators in each of the plurality of sensors are characterized by corresponding first and second polynomials, respectively, and wherein, during operation of the integrated circuit, a voltage and a temperature sensed by each of the plurality of sensors is determined by a control circuit solving for a voltage and temperature using respective frequencies of the first and second output signals and the first and second polynomials.
15. The integrated circuit as recited in claim 9 , wherein each of the plurality of sensors is coupled to receive a supply voltage that is provided to each of the circuits in the one of the plurality of functional circuit blocks in which it is implemented.