Light source monitoring
A system such as an imaging system may include an illumination module. The illumination module may include a light source monitoring system. The light source monitoring system may sample a light source signal and aggregate the samples into data chunks. The light source monitoring system may selectively aggregate the data chunks to form groups of a monitoring time window. The light source monitoring system may detect a fault based on a value characterizing light source performance during the monitoring time window.
1 . An imaging system comprising:
a sensor module having an image sensor pixel array; and
an illumination module having a light source, driver circuitry coupled to the light source, and a light source monitoring system coupled to the light source and configured to receive a light source signal, wherein the light source monitoring system comprises:
a data chunking circuit that produces a plurality of data chunk values based on samples from the light source signal;
a grouping circuit that produces a plurality of group values each aggregating at least some of the plurality of data chunk values; and
a failure detection circuit that produces an output signal indicative of a fault based on a monitoring time window characterized by at least some of the plurality of group values.
2 . The imaging system defined in claim 1 , wherein the plurality of data chunk values each comprise information about multiple samples.
3 . The imaging system defined in claim 2 , wherein the information about multiple samples comprises times at which the light source signal is asserted.
4 . The imaging system defined in claim 2 , wherein the plurality of group values each comprise a sum of multiple data chunk values.
5 . The imaging system defined in claim 4 , wherein the failure detection circuit produces an additional sum for the monitoring time window that adds the at least some of the plurality of group values.
6 . The imaging system defined in claim 5 , wherein the failure detection circuit performs a comparison of the additional sum with one or more threshold levels and produces the output signal based on the comparison.
7 . The imaging system defined in claim 6 , wherein the monitoring time window is a rolling time window that changes over time and wherein the additional sum is a rolling sum that changes over time.
8 . The imaging system defined in claim 1 , wherein the failure detection circuit monitors the monitoring time window for a first monitoring channel of the light source signal and monitors one or more additional monitoring time windows for one or more additional monitoring channels of the light source signal.
9 . The imaging system defined in claim 1 , wherein the light source monitoring system is electrically connected to a path between the light source and the driver circuitry that conveys a drive signal from the driver circuitry to the light source and wherein the light source signal is the drive signal.
10 . The imaging system defined in claim 1 , wherein the light source monitoring system comprises a light detector and wherein the light source signal is based on light emitted by the light source and detected by the light detector.
11 . An illumination module comprising:
a light source; and
a light source monitoring system coupled to the light source and configured to receive a light source signal, wherein the light source monitoring system comprises:
a counter configured to produce samples of the light source signal;
a plurality of averaging circuits coupled to the counter;
a multiplexer having a plurality of inputs coupled to the plurality of averaging circuits and having an output;
a first summation circuit coupled to the output of the multiplexer;
a memory circuit coupled to the first summation circuit;
a second summation circuit coupled to the memory circuit and the first summation circuit; and
a comparison circuit coupled to the second summation circuit.
12 . The illumination module defined in claim 11 , wherein a given averaging circuit of the plurality of averaging circuits produces a set of average values over time and wherein the first summation circuit produces a set of group values over time based on the set of average values.
13 . The illumination module defined in claim 12 , wherein the memory circuit stores the set of group values, and wherein the second summation circuit produces a rolling sum over time based on the set of group values.
14 . The illumination module defined in claim 11 further comprising:
an adder circuit; and
a multiplier circuit, wherein the adder circuit and the multiplier circuit are coupled between the counter and the plurality of averaging circuits.
15 . The illumination module defined in claim 14 further comprising:
a plurality of ceiling circuits that perform a ceiling function on outputs of the plurality of averaging circuits and that are coupled between the plurality of averaging circuits and the multiplexer.
16 . The illumination module defined in claim 15 further comprising:
a group value shifting circuit that changes a number of bits of an output of the first summation circuit and that is coupled between the first summation circuit and the memory circuit.
17 . A time-of-flight sensor comprising:
a sensor module having an image sensor pixel array; and
an illumination module having a light source, driver circuitry coupled to the light source, and a light source monitoring system coupled to the light source and configured to receive a drive signal provided from the driver circuitry to the light source, wherein the light source monitoring system comprise:
a first monitor configured to detect one or more faults using the drive signal and using a first observation time window having a first duration; and
a second monitor configured to detect the one or more faults using the drive signal and using a second observation time window having a second duration.
18 . The time-of-flight sensor defined in claim 17 , wherein the first monitor produces a first value for the first observation time window based on a first set of average values aggregated from samples of the drive signal and wherein the second monitor produces a second value for the second observation time window based on a second set of averages values aggregated from the samples of the drive signal.
19 . The time-of-flight sensor defined in claim 18 , wherein the first set of average values has average values that each contain information about a first number of samples and wherein the second set of average values has average values that each contain information about a second number of samples greater than the first number of samples.
20 . The time-of-flight sensor defined in claim 18 , wherein the second set of average values has a greater number of average values than the first set of average values.