Hall-effect-based magnetic field sensor having an improved output bandwidth
A magnetic field sensor formed by a Hall cell having a first, second, third and fourth conduction nodes electrically coupled together by resistive paths. Flowing between the first and second conduction nodes is a control current. In the presence of a magnetic field, a difference of potential due to the Hall effect is generated between the third and fourth conduction nodes. An operational amplifier has an inverting input terminal coupled to the fourth conduction node, a non-inverting input terminal biased at the voltage at the third conduction node, and an output terminal coupled in feedback mode to the inverting input by a feedback resistor. The current generated in feedback through the feedback resistor generates a voltage indicating unbalancing, due to the Hall effect, between the third and fourth conductive nodes, and consequently indicates the intensity of the magnetic field that acts upon the Hall cell.
1. A circuit, comprising:
a Hall effect cell having first, second, third and fourth nodes;
a first circuit having a first input coupled to the third node, a second input coupled to receive a non-zero force voltage and an output coupled to the first node, said first circuit configured to bias the first node at a first voltage and further provide a bias current flowing through the Hall effect cell from the first node to the second node; and
a second circuit having a first input coupled to the fourth node, a second input coupled to receive a non-zero offset voltage different from said non-zero force voltage and an output coupled by a feedback resistor to the fourth node to maintain the fourth node at the non-zero offset voltage and generate an output voltage across terminals of said feedback resistor having a magnitude corresponding to an intensity of a magnetic field acting on the Hall effect cell and a sign corresponding to a direction of said magnetic field.
2. The circuit of claim 1 , wherein the first circuit comprises a differential amplifier circuit having an inverting input coupled to the third node, a non-inverting input coupled to receive the non-zero force voltage and an output coupled to the first node.
3. The circuit of claim 1 , wherein the second circuit comprises a differential amplifier circuit having an inverting input coupled to the fourth node and a non-inverting input coupled to receive the non-zero offset voltage, said feedback resistor coupled between an output of the differential amplifier and the inverting input.
4. The circuit of claim 1 , further comprising a current spinning circuit configured to spin application of the bias current to the first through fourth nodes and further configured to spin coupling of the first inputs of the first and second circuits to the first through fourth nodes.
5. A magnetic field sensor circuit, comprising:
a first Hall cell having a first, second, third and fourth conduction nodes wherein, in an operating condition relating to presence of a magnetic field acting upon the first Hall cell, a Hall voltage is generated between said third and fourth conduction nodes;
a first biasing circuit operatively coupled between said first and third conduction nodes and configured to bias the first conduction node at a first operating voltage and generate a flow of a control current between the first and second conduction nodes to drive the third conduction node to a non-zero force voltage;
a second biasing circuit having a first input terminal operatively coupled to the fourth conduction node, a second input terminal adapted to receive a non-zero offset voltage that is different from the non-zero force voltage and an output terminal coupled in a feedback mode to the first input by a feedback resistor;
wherein the second biasing circuit is configured to generate, in the presence of the magnetic field, a feedback current through the feedback resistor to maintain the fourth conduction node at the non-zero offset voltage; and
wherein an output voltage across the feedback resistor in response to said feedback current indicates an intensity and direction of said magnetic field.
6. The magnetic field sensor according to claim 5 , wherein said first biasing circuit includes a first operational amplifier having a first input terminal electrically coupled to said third conduction node, a second input terminal biased at the non-zero force voltage and an output terminal coupled to the first conduction node.
7. The magnetic field sensor according to claim 6 , wherein the second biasing circuit includes a second operational amplifier having said first input terminal coupled as an inverting input, said second input terminal coupled as a non-inverting input to receive the non-zero offset voltage, and said output terminal coupled as an output terminal.
8. The magnetic field sensor according to claim 5 , further comprising a current-spinning circuit coupled to the first Hall cell.
9. The magnetic field sensor according to claim 5 , wherein said non-zero offset voltage differs from the non-zero-force voltage by a value such that, in the absence of magnetic field, said output voltage signal has a value equal to said non-zero force voltage.
10. The magnetic field sensor according to claim 5 , further comprising a second Hall cell having first, second, third and fourth conduction nodes, wherein the first conduction nodes of the first and second Hall cells are directly connected to each other, the third conduction nodes of the first and second Hall cells are directly connected to each other and the fourth conduction nodes of the first and second Hall cells are directly connected to each other.