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EP-4035269-B1 - POR CIRCUIT

EP4035269B1EP 4035269 B1EP4035269 B1EP 4035269B1EP-4035269-B1

Inventors

  • XU, Weichen
  • MARTINS, Gustavo Campos

Dates

Publication Date
20260506
Application Date
20200925

Claims (13)

  1. A Power-On Reset, POR, circuit for generating a control signal to power-on a load, such as a wireless sensor node, for resetting at least one register of said load, when a supply voltage supplied to said load exceeds a predetermined value, said POR circuit comprising: - a voltage reference generator arranged for generating a first reference voltage and a second reference voltage, wherein said first reference voltage and second reference voltage is nonlinear dependent of said supply voltage, wherein said second reference voltage differs from said first reference voltage; - switching means arranged for selecting said first reference voltage or said second reference voltage; - a voltage divider arranged for creating a threshold voltage, wherein said threshold voltage is a fraction of said supply voltage; - a voltage comparator arranged for comparing said selected first or second reference voltage with said threshold voltage, wherein said voltage comparator generates a first output voltage when said threshold voltage is above said first reference voltage and a second output voltage when said threshold voltage is below said second reference voltage, wherein said voltage divider comprises NMOS and/or PMOS transistors operating in cut-off region, and wherein said voltage reference generator comprises of at least one NMOS or PMOS transistor operating in cut-off region in series connected to a plurality of diode connected NMOS and/or PMOS transistors.
  2. A POR circuit according to any of the previous claims, wherein said first output voltage is a low voltage, for example 0 volts, and said second output voltage is a high voltage, for example equal to said supply voltage.
  3. A POR circuit according to any of the previous claims, wherein said first output voltage is a low voltage, for example 0 volts, and said second output voltage is equal to said maximum supply voltage.
  4. A POR circuit according to any of the previous claims, wherein said first output voltage is a high voltage, for example equal to said supply voltage, and said second output voltage is a low voltage, for example 0 volts.
  5. A POR circuit according to any of the previous claims, wherein said switching means comprise of at least one switch.
  6. A POR circuit according to any of the previous claims, wherein said switching means comprise of two switches.
  7. A POR circuit according to any of the previous claims, wherein said switching means comprise of at least one NMOS and/or PMOS transistor.
  8. A POR circuit according to any of the previous claims, wherein said first reference voltage and said second reference voltage is determined by selecting transistors having corresponding W/L characteristics.
  9. A POR circuit according to any of the previous claims, wherein said POR circuit is further comprising at least one gain stage arranged for amplifying said output voltage of said voltage comparator.
  10. A POR circuit according to any of the previous claims, wherein said at least one gain stage comprises NMOS and/or PMOS transistors.
  11. A POR circuit according to any of the previous claims, wherein said POR circuit comprises NMOS and/or PMOS transistors.
  12. A POR circuit according to any of the previous claims, wherein said voltage divider is a linear voltage divider.
  13. APOR circuit according to any of the previous claims, wherein said voltage reference generator comprises of a single stage of transistors connected in series.

Description

Technical field The present invention relates, in general, to a Power-On Reset, POR, circuit for generating a control signal to power-on a load, such as a wireless sensor node, for resetting at least one register of said load, with improved efficiency and cold-start capability. Background A Power-On-Reset, POR, circuit is an electronic circuit that detects if power is applied to a given electrical device and generates a control signal to the entire device circuit placing it into a known state. The purpose of a POR circuit is to delay start of operation of the device after power is applied until the supply voltage reaches a predetermined nominal value and stabilizes at the correct levels. This ensures that clocks of the processors settle accurately and loading of internal registers is complete before the device actually starts working or gets switched on. Internet-of-Things, loT, devices or Wireless Sensor Nodes, WSNs, used in various monitoring and sensing applications typically rely on energy harvesting sources. These Plug & Forget devices minimize the need for human intervention, ensure continuous operation for years or even decades and are very environment friendly. The device can further be equipped with an additional power source like a battery or capacitor, which is charged with the energy harvester. The main drawback of harvesting energy from ambient sources is that the energy present in available energy sources, like temperature difference, light or Radio Frequency signals, is very low. Typically, these available power levels fall below circuit threshold values which are necessary to start up initially. Current solutions for achieving a low power start up require the use of bulky peripheral circuits like off-chip transformers, logic gates and latches, leading to undesired area overhead and large footprint. POR circuits are known and available with a variety of requirements, which may be optimized for particular purposes. A known example can be seen in US 6 650 155 B1. In known POR circuits there always is a trade-off between optimizations like efficiency or cold-start capability. In loT and WSN applications it is however preferable that both requirements are met. To ensure device operation even with weak sources of ambient energy, it is necessary that POR circuits applied in energy harvesting systems consume ultra-low power.. Furthermore, because of the weak sources of ambient power, the cold start problem is a challenging problem for energy harvesting devices equipped with a POR circuit. At the moment the POR control signal prompts the main function of the device that enough power is available, the device starts working in normal operation mode. This results in a power consumption peak causing a drop of the supply voltage below threshold level of the POR circuit, that in turn a new POR signal is generated instructing the device to stop normal operation mode because not enough power is available. The device will keep toggling between on and off for a long time or even never start operating properly. In view of the above, there is a need for a POR circuit with improved efficiency and cold-start capability. Summary It is an object of the present invention to provide a Power-On Reset, POR, circuit for generating a control signal to power-on a load, such as a wireless sensor node, for resetting at least one register of said load, with improved efficiency and cold-start capability. In a first aspect of the invention, this object is provided by a Power-On Reset, POR, circuit as claimed in claim 1. Internet-of-Things, IoT, and Wireless Sensor Nodes, WSN, devices with energy harvesters may be configured to have different operating modes. In, for example, a first operating mode, the circuit or device may be starting-up and in a second operating mode, the circuit or device may be (fully) operational. The device is typically equipped with a POR circuit arranged for generating a control signal to the device to ensure the device is in a known state before the device actually starts working. After power is applied the start of the second operation mode is delayed until the supply voltage reaches a predetermined nominal value and stabilizes at the correct level. These IoT or WSN devices that are powered (primarily) from an energy harvesting source are dependent on the low input power of the energy harvester. Without the energy harvesters, the device typically depend to heavily on its primary power supply, i.e. the battery, such that battery replacement is required over a certain time period. The use of the energy harvester may thus significantly postpone or even completely remove the need for replacement of the battery. In order for the energy harvester to be effective, the POR circuit must be capable of cold-start. This means that the energy harvester may, during his first start-up phase, have a battery which fails to provide a sufficient supply voltage for the device to operate, e.g. due to a fully depleted batt