Frequency detector and oscillator circuits are disclosed. Example frequency detector and oscillator circuits disclosed herein include a current approximation circuit coupled to an external clock operating at a target frequency. In some examples, the current approximation circuit is configured to determine a magnitude of a first current to charge a capacitor to reach a reference voltage during a first set of clock cycles generated by the external clock. In some examples, the current approximation circuit is further configured to generate an output current based on the magnitude of the first current and to use the output current to produce a comparator output. In some examples, the frequency detector and oscillator circuits further include a latching circuit coupled to receive the comparator output from the current approximation circuit. In some such examples, the latching circuit is configured to generate oscillating signals at the target frequency based on the comparator output.

A method for measuring frequency domain characteristics of a PDN having an output terminal connected to a power supply end of a functional circuit. The method includes: a to-be-measured output interface of the functional circuit is acquired; the to-be-measured output interface is controlled to output a first level signal having a first preset rule; remaining at least one output interface of the functional circuit, other than the to-be-measured output interface, is controlled to output a second level signal having a second preset rule according to a first frequency; changing voltage values corresponding to the first frequency and output by the to-be-measured output interface are acquired; and a characteristic impedance of the PDN at the first frequency is determined based on the changing voltage values corresponding to the first frequency.

A method for measuring frequency domain characteristics of a PDN having an output terminal connected to a power supply end of a functional circuit. The method includes: a to-be-measured output interface of the functional circuit is acquired; the to-be-measured output interface is controlled to output a first level signal having a first preset rule; remaining at least one output interface of the functional circuit, other than the to-be-measured output interface, is controlled to output a second level signal having a second preset rule according to a first frequency; changing voltage values corresponding to the first frequency and output by the to-be-measured output interface are acquired; and a characteristic impedance of the PDN at the first frequency is determined based on the changing voltage values corresponding to the first frequency.

A method for providing a frequency of an electrical quantity in an electrical power system comprises obtaining, with respect to a first time, a first discrete Fourier transform (DFT) phasor of an electrical quantity in the electrical power system, estimating a second DFT phasor at a time interval before the first time, where the time interval depends on an approximated frequency, and determining the frequency at the first time based on the first and the second DFT phasor.

A method for providing a frequency of an electrical quantity in an electrical power system comprises obtaining, with respect to a first time, a first discrete Fourier transform (DFT) phasor of an electrical quantity in the electrical power system, estimating a second DFT phasor at a time interval before the first time, where the time interval depends on an approximated frequency, and determining the frequency at the first time based on the first and the second DFT phasor.

A method and apparatus for converting an input frequency to a voltage signal using a passive band-pass filter. The method includes providing an input signal having a specified frequency and amplitude to a passive band-pass filter. The method also includes obtaining an attenuated signal corresponding to the input signal from the passive band-pass filter. The method also includes providing the attenuated signal to a peak detector to obtain a direct current (DC) signal having an output voltage proportional to the specified frequency. The passive circuitry includes a first circuit to receive an input signal having a specified frequency and amplitude, and output an attenuated signal corresponding to the input signal. The passive circuitry also includes a second circuit to convert the attenuated signal to a DC signal having an output voltage proportional to the specified frequency.

A method and apparatus for converting an input frequency to a voltage signal using a passive band-pass filter. The method includes providing an input signal having a specified frequency and amplitude to a passive band-pass filter. The method also includes obtaining an attenuated signal corresponding to the input signal from the passive band-pass filter. The method also includes providing the attenuated signal to a peak detector to obtain a direct current (DC) signal having an output voltage proportional to the specified frequency. The passive circuitry includes a first circuit to receive an input signal having a specified frequency and amplitude, and output an attenuated signal corresponding to the input signal. The passive circuitry also includes a second circuit to convert the attenuated signal to a DC signal having an output voltage proportional to the specified frequency.

A method and apparatus for converting an input frequency to a voltage signal using a passive band-pass filter. The method includes providing an input signal having a specified frequency and amplitude to a passive band-pass filter. The method also includes obtaining an attenuated signal corresponding to the input signal from the passive band-pass filter. The method also includes providing the attenuated signal to a peak detector to obtain a direct current (DC) signal having an output voltage proportional to the specified frequency. The passive circuitry includes a first circuit to receive an input signal having a specified frequency and amplitude, and output an attenuated signal corresponding to the input signal. The passive circuitry also includes a second circuit to convert the attenuated signal to a DC signal having an output voltage proportional to the specified frequency.

A method and apparatus for converting an input frequency to a voltage signal using a passive band-pass filter. The method includes providing an input signal having a specified frequency and amplitude to a passive band-pass filter. The method also includes obtaining an attenuated signal corresponding to the input signal from the passive band-pass filter. The method also includes providing the attenuated signal to a peak detector to obtain a direct current (DC) signal having an output voltage proportional to the specified frequency. The passive circuitry includes a first circuit to receive an input signal having a specified frequency and amplitude, and output an attenuated signal corresponding to the input signal. The passive circuitry also includes a second circuit to convert the attenuated signal to a DC signal having an output voltage proportional to the specified frequency.

A circuit for an inductive conductivity sensor comprises: a secondary coil having a first coil terminal and a second coil terminal, a switch having a first switch terminal, a second switch terminal, a third switch terminal, a first potential terminal, and a control unit having a first control terminal and a second control terminal, wherein the first coil terminal is connected to the first control terminal and the second coil terminal is connected to the first switch terminal, wherein the second switch terminal is connected to the first potential terminal and the third switch terminal is connected to the second control terminal.