Measuring Process of the Average Frequency of an Alternating Signal, and Corresponding Electronic Circuit
AssigneeSTMicroelectronics (Grenoble 2) SAS
InventorPascal Mellot
Life of this patent
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Abstract
In an embodiment, a method for measuring an average frequency of an AC signal includes receiving the AC signal, triggering a first counter that is clocked at a first frequency, detecting each zero crossing of the AC signal in a predetermined crossing direction, recording a value of the first counter at each detected zero crossing, incrementing a second counter at each detected zero crossing, and calculating the average frequency of the AC signal based on the first frequency, a last recorded value of the first counter, and a last value of the second counter.
Claims23
A method for measuring an average frequency of an AC signal, the method comprising:
- receiving the AC signal during a measuring period that has a beginning and an end;
- triggering a first counter that is clocked at a first frequency higher than a maximum frequency of the AC signal;
- detecting each zero crossing of the AC signal in a predetermined crossing direction starting from the beginning of the measuring period;
- recording a value of the first counter at each detected zero crossing;
- triggering a second counter with an initial counter value at a first zero crossing of the AC signal in the predetermined crossing direction;
- incrementing the second counter at each subsequent zero crossing of the AC signal in the predetermined crossing direction;
- calculating a duration of a portion of the AC signal based on the first frequency and on a first and last recorded values of the first counter;
- and
- calculating the average frequency of the AC signal based on the duration, the initial counter value and a last value of the second counter.
An electronic circuit comprising:
- a first counter configured to be clocked at a first frequency;
- a second counter;
- a first control circuit configured to receive, during a measuring period, an AC signal having a maximum frequency that is lower than the first frequency, wherein the first control circuit is configured to:
- trigger the first counter,
- detect, starting from a beginning of the measuring period, each zero crossing of the AC signal in a predetermined crossing direction,
- record a current value of the first counter at each zero crossing of the AC signal in the predetermined crossing direction,
- trigger, at a first zero crossing of the AC signal in the predetermined crossing direction, a second counter with an initial counter value, and
- increment the second counter at each subsequent zero crossing of the AC signal in the predetermined crossing direction;
- and
- a module configured to:
- calculate, at an end of the measuring period, a duration of a portion of the AC signal based on the first frequency and of a first and a last recorded current values of the first counter, and
- calculate an average frequency of the AC signal based on the duration, the initial counter value and a last value of the second counter.
A system comprising:
- a photodiode coupled between a first supply terminal and a first node;
- a first switch coupled between the first node and a second supply terminal;
- a control module comprising a first comparator having an input coupled to the first node;
- and
- a second circuit comprising a preliminary counter having an input coupled to an output of the first comparator, and a measuring module having an input coupled to an output of the preliminary counter, the measuring module configured to generated an average frequency signal based on the output of the preliminary counter.
Dependencies are inferred from the claim text.