Sensor module
A sensor module includes: a count unit configured to generate first to n-th count values of a time event of one of a measurement target signal output from a physical quantity sensor and a reference periodic signal output from a reference periodic signal generation unit in synchronization with the other; a time digital value generation unit configured to generate first to n-th time digital values based on a phase difference between the measurement target signal and the reference periodic signal; and a combined output value generation unit configured to generate an i-th combined output value based on the i-th time digital value and the i-th count value. A quantization error of the j-th combined output value is fed back to generation of the (j+1)-th combined output value, and a period of a change in the physical quantity when a frequency, at which the physical quantity changes, is a maximum frequency is longer than eight times an average period in which first to n-th combined output values are generated.
1 . A sensor module comprising:
a physical quantity sensor configured to output a measurement target signal whose frequency changes according to a magnitude of a detected physical quantity;
a reference periodic signal generation unit configured to output a reference periodic signal;
a count unit configured to count a time event of one of the measurement target signal and the reference periodic signal in synchronization with the other of the measurement target signal and the reference periodic signal to generate first to n-th count values in time series, n being an integer of 2 or more;
a time digital value generation unit configured to generate first to n-th time digital values, each of which is based on a phase difference between the measurement target signal and the reference periodic signal, in time series; and
a combined output value generation unit configured to generate an i-th combined output value based on the i-th time digital value and the i-th count value, i being an integer between 1 to n, wherein
the combined output value satisfies a property of a delta-sigma modulation signal to obtain a noise shaping effect,
a quantization error of the j-th combined output value is fed back to generation of a (j+1)-th combined output value, j being an integer between 1 to n−1, and
a period of a change in the physical quantity, when a frequency at which the detectable physical quantity changes is a maximum frequency in a frequency band, is longer than eight times an average period in which the first to n-th combined output values are generated.
2 . The sensor module according to claim 1 , wherein
the time digital value generation unit is configured to generate the first to n-th time digital values by a multiphase clock method, a time and voltage conversion method, or a summation accumulated time to digital convert (ΣATDC) method.
3 . The sensor module according to claim 1 , wherein
the combined output value generation unit is configured to generate the first to n-th combined output values in time series at both a rising timing and a falling timing of the measurement target signal.
4 . The sensor module according to claim 1 , further comprising:
a filter unit in a stage subsequent to the combined output value generation unit.
5 . The sensor module according to claim 4 , wherein
the filter unit is configured to perform decimation processing on the first to n-th combined output values.
6 . The sensor module according to claim 4 , wherein
the combined output value generation unit is configured to generate the first to n-th combined output values in time series at both a rising timing and a falling timing of the measurement target signal, and
the filter unit is configured to perform moving average processing of even number taps on the first to n-th combined output values.
7 . The sensor module according to claim 1 , wherein
the combined output value generation unit is configured to generate the i-th combined output value by subtracting an offset value from a value obtained by combining the i-th time digital value and the i-th count value.
8 . The sensor module according to claim 1 , further comprising:
a storage unit configured to store p continuous combined output values among the first to n-th combined output values, wherein
the stored p combined output values are output from the storage unit based on a control signal.
9 . The sensor module according to claim 8 , wherein
each of the first to n-th combined output values is a value based on a time stamp difference, and
the storage unit is configured to further store one of the (k+1)-th to (k+p)-th count values when the (k+1)-th to (k+p)-th combined output values are stored as the p combined output values.
10 . The sensor module according to claim 8 , wherein
when the storage unit is a ring buffer and stores the (k+1)-th to (k+p)-th combined output values as the p combined output values, storing of the (k+p+1)-th combined output value and the subsequent combined output values is stopped and the (k+1)-th to (k+p)-th combined output values are output based on the control signal.
11 . The sensor module according to claim 10 , wherein
each of the first to n-th combined output values is a value based on a time stamp difference, and
the storage unit is configured to further store the (k+p)-th count value when the (k+1)-th to (k+p)-th combined output values are stored as the p combined output values, and the (k+1)-th to (k+p)-th combined output values and the (k+p)-th count value are output based on the control signal.
12 . A sensor module comprising:
one or more physical quantity sensors;
one or more count units;
one or more time digital value generation units;
one or more combined output value generation units;
one or more storage units; and
a reference periodic signal generation unit configured to output a reference periodic signal, wherein
the m-th physical quantity sensor is configured to output an m-th measurement target signal whose frequency changes according to a magnitude of a detected m-th physical quantity,
the m-th count unit is configured to count a time event of one of the m-th measurement target signal and the reference periodic signal in synchronization with the other of the m-th measurement target signal and the reference periodic signal to generate first to n-th count values in time series, n being an integer of 2 or more,
the m-th time digital value generation unit is configured to generate first to n-th time digital values, each of which is based on a phase difference between the m-th measurement target signal and the reference periodic signal, in time series,
the m-th combined output value generation unit is configured to generate an i-th combined output value based on the i-th time digital value generated by the m-th time digital value generation unit and the i-th count value generated by the m-th count unit, i being an integer wherein 1≤i≤n, wherein the combined output value satisfies a property of a delta-sigma modulation signal to obtain a noise shaping effect,
the m-th storage unit is configured to store p continuous combined output values among the first to n-th combined output values generated by the m-th combined output value generation unit, and the stored p combined output values are output based on a control signal,
a quantization error of the j-th combined output value generated by the m-th combined output value generation unit is fed back to generation of the (j+1)-th combined output value, j being an integer wherein 1≤j≤n−1, and
a period of a change of the m-th physical quantity, when a frequency at which the detectable m-th physical quantity changes is a maximum frequency in a frequency band, is longer than eight times an average period in which the first to n-th combined output values are generated by the m-th combined output value generation unit, m being an integer of 1 or more.