Voltage monitoring system and method for harvesting energy in a computational environment
A voltage monitoring system and a method for harvesting energy is disclosed. A system includes a ring oscillator circuit, which incorporates delay line circuit composed of series of inverting logic gates. The final inverting logic gate forms self-oscillating feedback loop by connecting its output to the input of the first logic gate. To interface with ring oscillator circuit, transistor-based voltage divider circuit is implemented. The transistor-based voltage divider circuit utilizes multiple diode-connected transistor devices, with bulk terminals interconnected to the respective source terminals. Enable signal controls final diode-connected transistor device at its gate terminal. Furthermore, a voltage-level shifter circuit is connected to output of inverting logic gates, enabling seamless integration with ring oscillator circuit. Finally, a counter circuit is linked to voltage-level shifter circuit, utilizing its output terminal. The counter circuit is connected to external system responsible for harvesting energy, which powers the computational task performed by the system.
1 . A voltage monitoring system comprising:
a ring oscillator circuit comprising a delay line circuit, wherein the delay line circuit comprises a series of inverting logic gates, each of the inverting logic gates comprising a first input terminal, a second input terminal and an intermediate output terminal, the series of inverting logic gates comprising a final inverting logic gate comprising a first input terminal, a second input terminal, an enable input terminal and a final output terminal, and the final output terminal of the final inverting logic gate being looped to the first input terminal of a first inverting logic gate to form a self-oscillating feedback loop;
a transistor-based voltage divider circuit connected to the ring oscillator circuit via the second input terminal of the inverting logic gates, the transistor-based voltage divider circuit comprising a plurality of diode connected transistor devices with each bulk terminal of diode connected transistor device connected to each source terminal of the diode connected transistor device, the plurality of diode connected transistor devices comprising a final diode connected transistor device fed with an enable signal at a gate terminal of the final diode connected transistor device;
a voltage-level shifter circuit connected to the ring oscillator circuit via an intermediate output terminal of the inverting logic gates; and
a counter circuit connected to the voltage-level shifter circuit via an output terminal of the voltage-level shifter circuit, the counter circuit being connected to an external system for harvesting energy to perform a computational task.
2 . The voltage monitoring system of claim 1 , wherein the ring oscillator circuit is to:
generate a ring oscillator frequency as a function of change in a supply voltage, and the ring oscillator frequency being dependent on an average gate delay of the inverting logic gates, and the average gate delay being directly proportional to at least one of a change in a diode connected transistor device size and the supply voltage.
3 . The voltage monitoring system of claim 1 , wherein the ring oscillator circuit is further to:
generate an output voltage level, the output voltage level of the ring oscillator circuit being lesser than an output voltage of the transistor-based voltage divider circuit, the output voltage of the transistor-based voltage divider circuit is a fractional value of the supply voltage; and
extract power from the transistor-based voltage divider circuit resulting in a voltage drop below a nominal voltage value, and the voltage drop being rectified by increasing width of the plurality of diode connected transistor devices.
4 . The voltage monitoring system of claim 1 , wherein the ring oscillator circuit is to:
measure a change in a ring oscillator frequency, wherein, when the change in the ring oscillator frequency is higher, an enable period of the ring oscillator circuit is decreased for operating the voltage monitoring system at one of a lower duty cycle and at a higher sampling rate, and the enable period corresponds to amount of time the ring oscillator circuit is powered to generate at least one sample and the sampling rate corresponds to a time between a distinct sample.
5 . The voltage monitoring system of claim 1 , wherein the transistor-based voltage divider circuit is to:
set an operating range for the ring oscillator circuit to tune the ring oscillator circuit to operate in a preferred voltage region, and the enable signal being fed to the gate terminal of the final diode connected transistor device changes a duty cycle of the ring oscillator circuit.
6 . The voltage monitoring system of claim 5 , wherein the preferred voltage region is determined based on a type of inverting logic gates and a ring oscillator operating voltage.
7 . The voltage monitoring system of claim 1 , wherein the voltage-level shifter circuit is to:
receive an intermediate output signal from the intermediate output terminals of the inverting logic gates, wherein the intermediate output signal comprises an output voltage level;
determine voltage difference between the output voltage level and a voltage level required by an intermittent computation circuit; and
generate a level-shifted output signal based on the determined voltage difference by shifting the output voltage level to the voltage level required by the intermittent computation circuit, wherein the level-shifted output signal comprises a voltage level required by the intermittent computation circuit.
8 . The voltage monitoring system of claim 7 , wherein the output voltage is shifted to the voltage level required by the intermittent computation circuit using a common ground of the transistor-based voltage divider circuit and the voltage-level shifter circuit to boost the output voltage.
9 . The voltage monitoring system of claim 1 , wherein the counter circuit is to:
generate a count value based on a ring oscillator frequency and a time per sample during which the voltage monitoring system is enabled.
10 . The voltage monitoring system of claim 9 , wherein the count value corresponds to a number of times an output signal from the final inverting logic gate traverses the self-oscillating feedback loop of the ring oscillator circuit during a fixed time period, and the count value indicates an available energy level in a buffer capacitor.
11 . The voltage monitoring system of claim 10 , wherein the count value is transmitted to a digital comparator for generating an interrupt signal and a request for determining available energy level in the buffer capacitor to perform the computational task.
12 . The voltage monitoring system of claim 1 , wherein the ring oscillator circuit comprises an odd-numbered series of inverting logic gates to generate a ring oscillator frequency which is inversely proportional to a supply voltage.
13 . The voltage monitoring system of claim 1 , wherein the ring oscillator circuit comprises a rate of oscillation depending on a propagation delay of the inverting logic gates, and the propagation delay in the ring oscillator circuit being based on a supply voltage of the voltage monitoring system.
14 . The voltage monitoring system of claim 1 , wherein the ring oscillator circuit comprises a voltage sensitivity which increases based on a chain length of the series of inverting logic gates.
15 . The voltage monitoring system of claim 1 , wherein the ring oscillator circuit is operated at a low voltage level to maximize linearity of a voltage-frequency transfer function.
16 . A computing system for harvesting energy comprising:
a hardware processor;
an intermittent computation circuit communicatively connected to the hardware processor, the intermittent computation circuit is to monitor a buffer capacitor voltage for the intermittent computation circuit;
a voltage monitoring system communicatively coupled to the intermittent computation circuit via the hardware processor, the voltage monitoring system comprises:
a transistor-based voltage divider circuit to tune a ring oscillator circuit by operating the ring oscillator circuit in a preferred voltage region, the transistor-based voltage divider circuit being supplied with a supply voltage;
the ring oscillator circuit to generate a voltage dependent ring oscillator frequency based on a tapped voltage of the transistor-based voltage divider circuit;
a voltage-level shifter circuit to generate a level shifted output signal by shifting a voltage level of an intermediate output signal received from the ring oscillator circuit, the generated level-shifted output signal corresponds to a voltage level required by the intermittent computation circuit; and
a counter circuit to generate a count value during a sampling period by incrementing an initial count value for each positive edge of the level-shifted output signal; and
the intermittent computation circuit is to determine available energy level for computation by monitoring the buffer capacitor voltage for the intermittent computation circuit, the buffer capacitor voltage being monitored by mapping the count value to values of a pre-defined supply voltage.
17 . The computing system of claim 16 , wherein the computing system further comprises a memory coupled to the hardware processor, wherein the memory comprises a set of instructions stored in the form of executable program, which when executed by the hardware processor, cause the hardware processor to:
measure the voltage dependent ring oscillator frequency for a range of supply voltage levels;
determine a performance parameter for each of the measured voltage dependent ring oscillator frequency, the performance parameter comprising a resolution level and a sample rate;
generating a level shifted output signal by shifting the voltage level of an intermediate output signal to a voltage level required by the intermittent computation circuit based on the determined performance parameter;
generating the count value during a sampling period by incrementing an initial count value for each positive edge of the generated level-shifted output signal;
determining an optimal supply voltage value for the intermittent computation circuit by mapping the count value to values of the pre-defined supply voltage; and
identifying an available energy level for computation based on the generated count values and determined optimal supply voltage value, the available energy level corresponds to a n-bit value stored onto a destination register of the intermittent computation circuit.
18 . The computing system of claim 16 , wherein the buffer capacitor voltage is monitored by mapping the count values to a values of a pre-defined supply voltage using a data point stored in a non-volatile memory (NVM).
19 . The computing system of claim 16 , wherein the intermittent computation circuit is further connected to an energy harvesting system.
20 . A method for harvesting energy using a digital voltage monitoring system, the method comprising:
measuring, by a hardware processor, a voltage dependent ring oscillator frequency at a ring oscillator circuit for a range of supply voltage levels;
determining, by the hardware processor, a performance parameter for each of the measured voltage dependent ring oscillator frequency, the performance parameter comprising a resolution level and a sample rate;
generating, by the hardware processor, a level shifted output signal by shifting voltage level of the ring oscillator circuit to a voltage level required by an intermittent computation circuit based on the determined performance parameter;
generating, by the hardware processor, a count value during a sampling period by incrementing an initial count value for each positive edge of the generated level-shifted output signal;
determining, by the hardware processor, an optimal supply voltage value for the intermittent computation circuit by mapping the count value to values of a pre-defined supply voltage; and
identifying, by the hardware processor, an available energy level for computation based on the generated count values and the determined optimal supply voltage value, the available energy level corresponds to a n-bit value stored onto a destination register of the intermittent computation circuit.