Electronic devices with electromagnetic interference correction
An electronic device may have a sensor and may have a radio-frequency signal transmitter. The sensor may be vulnerable to electromagnetic interference (EMI) from the radio-frequency (RF) signals. Therefore, circuitry in the device may determine whether measurements from the sensor have been impacted by EMI. To make this determination, a digital filter may be used. In particular, the digital filter may be a digital persistence filter that generates a signal if the sensor measurement is high for a time that corresponds with the known emission time of the RF signals. Alternatively, the digital filter may receive the sensor measurements in the digital domain and compare the sensor measurements to time-delayed sensor measurements to determine whether the sensor measurements have been impacted by EMI. Control circuitry may discard any of the sensor measurements, or measurements from one or more other sensors, in response to the sensor measurements being impacted by EMI.
1 . An electronic device, comprising:
a sensor configured to generate sensor measurements;
a transmitter configured to transmit radio-frequency signals; and
a digital filter configured to generate a signal in response to detecting electromagnetic interference in the sensor measurements, wherein the digital filter comprises an up-counter that is configured to be reset to a given value and to be clocked at a given frame rate, wherein the up-counter is configured to be reset to the given value when the sensor measurements are below a threshold, and wherein the up-counter is configured to overflow when the sensor measurements are above the threshold for a period of time longer than the given value divided by the given frame rate.
2 . The electronic device of claim 1 , further comprising:
control circuitry configured to discard the sensor measurements in response to the signal from the digital filter.
3 . The electronic device of claim 1 , wherein the digital filter comprises a digital persistence filter, the electronic device further comprising:
a comparator between the sensor and the digital filter.
4 . The electronic device of claim 3 , wherein the up-counter is configured to be incrementally increased at the given frame rate when the sensor measurements are above the threshold.
5 . The electronic device of claim 4 , wherein the overflow of the up-counter is configured to form the signal generated by the digital filter.
6 . The electronic device of claim 3 , wherein the sensor is configured to generate the sensor measurements at a given burst rate, and wherein the up-counter comprises a marked-frame counter.
7 . The electronic device of claim 6 , wherein the marked-frame counter is configured to be incrementally increased in response to a number of the sensor measurements being over a frame threshold.
8 . The electronic device of claim 7 , wherein the signal from the digital filter is configured to be output in response to the marked-frame counter being over a marked-frame threshold after an observation window has elapsed.
9 . The electronic device of claim 3 , further comprising:
a hysteresis circuit coupled between an output of the comparator and an input of the comparator.
10 . The electronic device of claim 1 , wherein the digital filter is configured to receive the sensor measurements directly.
11 . The electronic device of claim 10 , wherein the digital filter is configured to compare the sensor measurements to time-delayed sensor measurements to determine whether there is electromagnetic interference in the sensor measurements.
12 . The electronic device of claim 11 , wherein the digital filter is configured to generate the signal in response to a difference between the sensor measurements and the time-delayed sensor measurements being greater than a difference threshold.
13 . An apparatus, comprising:
a sensor configured to generate sensor measurements at a given burst rate;
a comparator configured to output a respective indicator in response to each of the sensor measurements; and
a digital persistence filter configured to determine, based on the respective indicator, whether there is electromagnetic interference in each of the sensor measurements, wherein the digital persistence filter comprises a marked-frame counter that is configured to be reset to a given value and to be clocked at a given frame rate.
14 . The apparatus of claim 13 , wherein the sensor is selected from the group consisting of: a temperature sensor, an accelerometer, a gyroscope, an ambient light sensor, a humidity sensor, a heart rate sensor, and a blood oxygen sensor.
15 . The apparatus of claim 13 , further comprising:
control circuitry that is configured to discard given sensor measurements in response to the digital persistence filter determining that the given sensor measurements have been subject to electromagnetic interference.
16 . The apparatus of claim 13 , wherein the marked-frame counter is configured to be incrementally increased in response to a number of the sensor measurements being over a frame threshold.
17 . The apparatus of claim 16 , wherein the digital persistence filter is configured to output a signal in response to the marked-frame counter being over a marked-frame threshold after an observation window has elapsed.
18 . An electronic device, comprising:
a transmitter configured to transmit radio-frequency signals;
a circuit, comprising:
a sensor configured to generate sensor measurements; and
a digital persistence filter configured to generate a signal in response to detecting electromagnetic interference in the sensor measurements, wherein the digital persistence filter comprises an up-counter that is configured to be reset to a given value and to be clocked at a given frame rate, wherein the up-counter is configured to be reset to the given value when the sensor measurements are below a threshold, and wherein the up-counter is configured to overflow when the sensor measurements are above the threshold for a period of time longer than the given value divided by the given frame rate; and
control circuitry configured to disregard given sensor measurements in response to the signal.