Energy harvesting interface with improved impedance matching, method for operating the energy harvesting interface, and energy harvesting system using the energy harvesting interface

An energy harvesting interface, comprising:

• a first switch and a second switch coupled together in series between a first input terminal and a first output terminal;
• a third switch and a fourth switch connected together in series between a second input terminal and the first output terminal;
• a first charge-transfer element coupled between the first input terminal and the second output terminal;
• a second charge-transfer element coupled between the second input terminal and the second output terminal;
• and
• a first electrical-signal-detecting device coupled across the second switch and configured to detect whether an electric storage current that flows through the second switch reaches a first threshold value, said electric storage current being associated to an electrical charge stored in an input storage element;
• a second electrical-signal-detecting device coupled across the fourth switch and configured to detect whether an electric supply current that flows through the fourth switch reaches a second threshold value lower than the first threshold value;
• wherein, when the first threshold value has been reached, the first and second electrical-signal detecting devices co-operate for generating said second threshold value;
• and
• a control logic configured to:
• close the first, second, third, and fourth switches until the electric storage current reaches the first threshold value;
• open the first switch, thus generating the electric supply current for supplying an output second storage element through the first charge-transfer element by discharging the input storage element;
• and
• keep the first switch open as long as the electric supply current is higher than said second threshold value;
• wherein the first electrical-signal-detecting device comprises:
• a first comparator coupled across the second switch for comparing the value of the electric storage current with the first threshold value;
• and
• a current mirror configured to generate a scaled copy, scaled by a first proportionality factor, of the electric storage current;
• and
• wherein the second electrical-signal-detecting device comprises:
• a scaling resistor having a value of resistance that is equal to the value of resistance of the fourth switch multiplied by a second proportionality factor that is coupled between the fourth switch and an intermediate node and configured to generate, on the intermediate node, a sum voltage signal given by the sum of the voltage signal across the fourth switch, which is a function of the output current, and the voltage signal across the scaling resistor, which is a function of said scaled copy of the electric storage current;
• and
• a second comparator, having a first conduction terminal biased at a reference voltage of a zero value and a second conduction terminal coupled to the intermediate node, configured to generate a comparison signal identifying a condition in which the sum voltage signal has a substantially zero value.

An energy harvesting system configured to supply an electrical load, comprising:

• a transducer configured to convert energy coming from an energy source external to said system into a transduced electrical signal;
• an electrical-energy harvesting interface, configured to receive at input the transduced electrical signal and supply at output an output signal;
• and
• an electrical-energy storage element coupled to the output terminals of the electrical-energy harvesting interface for receiving at input the output signal, and configured to store electrical energy configured to supply the electrical load;
• wherein the electrical-energy harvesting interface comprises:
• a first switch and a second switch coupled together in series between a first input terminal and a first output terminal;
• a third switch and a fourth switch connected together in series between a second input terminal and the first output terminal;
• a first charge-transfer element coupled between the first input terminal and the second output terminal;
• a second charge-transfer element coupled between the second input terminal and the second output terminal;
• and
• a first electrical-signal-detecting device coupled across the second switch and configured to detect whether an electric storage current that flows through the second switch reaches a first threshold value, said electric storage current being associated to an electrical charge stored in said transducer;
• a second electrical-signal-detecting device coupled across the fourth switch and configured to detect whether an electric supply current that flows through the fourth switch reaches a second threshold value lower than the first threshold value;
• and
• a control logic configured to:
• close the first, second, third, and fourth switches until the electric storage current reaches the first threshold value;
• open the first switch, thus generating the electric supply current for supplying the electrical-energy storage element through the first charge-transfer element by discharging the transducer;
• and
• keep the first switch open as long as the electric supply current is higher than said second threshold value;
• wherein the first electrical-signal-detecting device comprises a circuit mirror configured to generate a scaled copy, scaled by a first proportionality factor, of the electric storage current as said second threshold;
• and
• wherein the second electrical-signal-detecting device comprises a current comparator configured to compare the electric supply current to the scaled copy of the electric storage current as said second threshold.

A method for harvesting energy, comprising:

• closing first, second, third, and fourth switches of an energy harvesting interface, wherein the first switch and the second switch are connected together in series between a first input terminal and a first output terminal, and wherein the third switch and the fourth switch are connected together in series between a second input terminal and the first output terminal;
• detecting electric storage current that flows through the closed second switch;
• keeping the first, second, third and fourth switches closed until the detected electric storage current reaches a first threshold current, said electric storage current being associated to electrical charge stored in an input storage element;
• generating a second threshold current that equals a peak value of the electric storage current multiplied by a proportionality factor;
• opening the first switch thus generating an electric supply current for supplying an output storage element through a first charge-transfer element by discharging the input storage element;
• detecting the electric supply current that flows through the closed fourth switch;
• comparing the detected electric supply current to the second threshold current
• keeping the first switch open as long as the detected electric supply current is higher than the second threshold current.

An energy-scavenging method, comprising:

• closing first, second, third, and fourth switches of an energy harvesting interface, wherein the first switch and the second switch are connected together in series between a first input terminal and a first output terminal, and wherein the third switch and the fourth switch are connected together in series between a second input terminal and the first output terminal;
• detecting electric storage current that flows through the closed second switch;
• keeping the first, second, third and fourth switches closed until the detected electric storage current reaches a first threshold value, said electric storage current being associated to electrical charge stored in an input storage element;
• opening the first switch thus generating an electric supply current for supplying an output storage element through a first charge-transfer element by discharging the input storage element;
• detecting the electric supply current that flows through the closed fourth switch;
• keeping the first switch open as long as the electric supply current is higher than a second threshold value that is lower than the first threshold value;
• wherein detecting the electric supply current that flows through the closed fourth switch comprises:
• comparing the electric current that flows through the second switch with the first threshold value and, in the case where said electric current through the second switch is equal to or higher than the first threshold value, then:
• generating a scaled copy, reduced by a first proportionality factor, of the electric current that flows through the second switch;
• and
• generating a multiple of said scaled copy by multiplying said scaled copy by a second proportionality factor to obtain said second threshold value.