A circuit for a passive radio frequency identification (RFID) tag with a temperature sensor, comprising:
- a resonance inductor and a resonance capacitor connected in parallel for coupling an external magnetic field;
- a clock recovery circuit;
- a rectifier circuit;
- a regulator circuit;
- a command demodulation circuit;
- a load modulator circuit;
- a bandgap reference circuit;
- a power-on reset circuit;
- an embedded memory module;
- other RFID tag circuits including a state machine control circuit, an energy level detection and limiting control circuit, a mode conversion circuit, and a reference voltage and bias current circuit;
- and a first energy storage capacitor, wherein:
- a positive terminal and a negative terminal of the resonance capacitor are respectively connected to two input terminals of each of the clock recovery circuit, the rectifier circuit, the command demodulation circuit, and the load modulator circuit;
- an output terminal of the rectifier circuit is connected to an input terminal of the regulator circuit;
- and an output terminal of the regulator circuit is respectively connected to each of the bandgap reference circuit, the power-on reset circuit, the embedded memory module, the other RFID tag circuits, and the first energy storage capacitor;
- a control circuit for RFID tag/sensor mode conversion;
- a switch transistor, wherein:
- an output terminal of the command demodulation circuit is connected to the control circuit for the RFID tag/sensor mode conversion and is configured to demodulate information from an alternate current (AC) signal sent by a card reader to receive a command from the card reader, the command including a command for regular operations of an RFID chip under an RFID tag mode unrelated to the temperature sensor and a command for starting the temperature sensor under a temperature sensor mode sent by the card reader to the RFID tag that includes the temperature sensor;
- the control circuit for the RFID tag/sensor mode conversion is configured to control and configure the RFID tag according to the command from the card reader demodulated by the command demodulation circuit;
- and
- in response to the command containing the command for starting the temperature sensor, the control circuit for the RFID tag/sensor mode conversion enters the temperature sensor mode, and outputs a voltage to a gate terminal of a switch transistor to make conduction between a source terminal and a drain terminal of the switch transistor;
- a second energy storage capacitor;
- and
- a temperature measurement and A/D conversion circuit, wherein:
- the gate terminal of the switch transistor is connected to an output terminal of the control circuit for the RFID tag/sensor mode conversion;
- the drain terminal of the switch transistor is connected to the output terminal of the regulator circuit;
- the source terminal of the switch transistor is connected to the ground through the second energy storage capacitor;
- and
- the switch transistor is controlled by the control circuit for the RFID tag/sensor mode conversion to make conduction between the source terminal and the drain terminal to connect the second energy storage capacitor to form a circuit loop with the temperature measurement and A/D conversion circuit and the first energy storage capacitor.