Apparatuses and methods for electrical current sensing
The present disclosure relates to a magnetic field sensor circuit including at least one coil for measuring a magnetic field, a first stage amplifier circuit coupled to the coil and having a first transfer function with a pole at a first frequency, and a second stage amplifier circuit coupled to an output of the first stage amplifier circuit and having a second transfer function with a zero at the first frequency. In some embodiments, a temperature dependent frequency drift of the pole of the first transfer function corresponds to a temperature dependent frequency drift of the zero of the second transfer function.
1. A magnetic field sensor circuit, comprising:
at least one coil configured to measure a magnetic field;
a first stage amplifier circuit coupled to the at least one coil and having a first transfer function with a pole at a first frequency; and
a second stage amplifier circuit coupled to an output of the first stage amplifier circuit and having a second transfer function with a zero at the first frequency,
wherein a first filter circuit included in the first stage amplifier circuit is configured to have a temperature dependent frequency drift of the pole of the first transfer function,
wherein a second filter circuit included in the second stage amplifier circuit is configured to have a temperature dependent frequency drift of the zero of the second transfer function, and
wherein the temperature dependent frequency drift of the pole of the first transfer function corresponds to the temperature dependent frequency drift of the zero of the second transfer function.
2. The magnetic field sensor circuit of claim 1 , wherein:
the first stage amplifier circuit comprises a first RC filter coupled between an input and an output of a first amplifier, the first RC filter causing the pole at the first frequency,
the second stage amplifier circuit comprises a second RC filter coupled between an input and an output of a second amplifier, the second RC filter causing the zero at the first frequency, and
a resistor of the first RC filter and a resistor of the second RC filter are both implemented as silicided polysilicon resistors.
3. The magnetic field sensor circuit of claim 2 , wherein a ratio r of a temperature coefficient of the silicided polysilicon resistors and a temperature coefficient of a resistance of the at least one coil is within 0.9≤r≤1.2.
4. The magnetic field sensor circuit of claim 1 , wherein the second stage amplifier circuit is configured to have a pole of the second transfer function at a second frequency.
5. The magnetic field sensor circuit of claim 4 , wherein the second frequency of the pole of the second transfer function is lower than the first frequency of the zero of the second transfer function.
6. The magnetic field sensor circuit of claim 4 , further comprising:
an RC high-pass filter circuit coupled between the first stage amplifier circuit and the second stage amplifier circuit, the RC high-pass filter circuit having a third transfer function with a pole at a third frequency.
7. The magnetic field sensor circuit of claim 6 , wherein the third frequency is lower than the first frequency and lower than the second frequency.
8. The magnetic field sensor circuit of claim 6 , wherein one or more resistors of the RC high-pass filter circuit are implemented as non-silicided polysilicon resistors.
9. The magnetic field sensor circuit of claim 1 , further comprising:
a Hall sensor circuit coupled to an input of the second stage amplifier circuit.
10. The magnetic field sensor circuit of claim 9 , wherein the Hall sensor circuit comprises:
at least one spinning current Hall sensor; and
a chopper amplifier circuit coupled between the at least one spinning current Hall sensor and the second stage amplifier circuit.
11. The magnetic field sensor circuit of claim 10 , further comprising:
a first RC lowpass filter circuit coupled between an output of the chopper amplifier circuit and an input of the second stage amplifier circuit.
12. The magnetic field sensor circuit of claim 11 , wherein
the second stage amplifier circuit comprises a second RC lowpass filter coupled between an input and an output of an amplifier of the second stage amplifier circuit,
wherein a resistor of the second RC lowpass filter of the second stage amplifier circuit is implemented as silicided polysilicon resistor and one or more resistors of the first RC lowpass filter coupled between the output of the chopper amplifier circuit and the input of the second stage amplifier circuit is implemented as a non-silicided polysilicon resistor.
13. The magnetic field sensor circuit of claim 10 , wherein the Hall sensor circuit comprises a temperature dependent current source coupled to the at least one spinning current Hall sensor.
14. The magnetic field sensor circuit of claim 1 , wherein:
each of the at least one coil is configured to generate a respective measurement signal representative of the magnetic field,
the first stage amplifier circuit is configured to receive each respective measurement signal and apply the first transfer function thereto to generate at least one first stage output signal, and
the second stage amplifier circuit is configured to apply the second transfer function to the at least one first stage output signal or to at least one signal derived from the at least one first stage output signal to generate at least one second stage output signal.
15. A current sensor circuit, comprising:
a current rail;
a first coil arranged at a first position of the current rail;
a second coil arranged at a second position of the current rail;
a first stage differential amplifier circuit coupled to the first coil and the second coil and having a first transfer function with a pole at a first frequency; and
a second stage differential amplifier circuit coupled to an output of the first stage differential amplifier circuit and having a second transfer function with a zero at the first frequency,
wherein a temperature dependent frequency drift of the pole of the first transfer function corresponds to a temperature dependent frequency drift of the zero of the second transfer function.
16. The current sensor circuit of claim 15 , further comprising:
a first spinning current Hall sensor arranged at the first position of the current rail;
a first differential chopper amplifier circuit coupled between the first spinning current Hall sensor and the second stage differential amplifier circuit;
a second spinning current Hall sensor arranged at the second position of the current rail; and
a second differential chopper amplifier circuit coupled between the second spinning current Hall sensor and the second stage differential amplifier circuit.
17. A method of magnetic field sensing, comprising:
capturing a magnetic field with at least one coil;
coupling the at least one coil to a first stage amplifier circuit having a first transfer function with a pole at a first frequency; and
coupling an output of the first stage amplifier circuit to a second stage amplifier circuit having a second transfer function with a zero at the first frequency,
wherein a temperature dependent frequency drift of the pole of the first transfer function corresponds to a temperature dependent frequency drift of the zero of the second transfer function.