Low-power magnetic sensing device and magnetic switch device comprising the magnetic sensing device

A magnetic switch device configured to generate two distinct logic levels in response to a sensed magnetic field strength of an external magnetic field, the magnetic switch device comprising:

• at least one TMR element having a TMR resistance that varies with the external magnetic field;
• said at least one TMR element being coupled to a first power supply rail providing a supply voltage substantially independent of the external magnetic field;
• said at least one TMR element being further coupled to a third terminal of a first transistor, the first transistor being biased at a first terminal by a first bias voltage;
• wherein, at a reference field strength of the external magnetic field, the TMR resistance has a TMR reference resistance value, and the first bias voltage is adjustable to control a first current at a second terminal of the first transistor at a first reference current value;
• and
• wherein said at least one TMR element is configured such that, when the external magnetic field is varied around the reference field strength by a field strength delta, the TMR resistance varies around the TMR reference resistance value by a resistance delta, such that the first current modulates around the first reference current value by a current delta;
• wherein the magnetic switch device further comprises a second transistor biased at a first terminal of the second transistor by a second bias voltage, a second terminal of the second transistor being connected to the second terminal of the first transistor at a node;
• and
• wherein the second bias voltage is adjustable to control a second current at the second terminal of the second transistor such that the second current is substantially equal to the first reference current value of the first transistor,
• wherein a polarity of the field strength delta determines which one of the two distinct logic levels is generated by the magnetic switch device.