Ambient light sensing system and method for measuring ambient light during pixel on and off periods
The present disclosure provides an ambient light sensing system including an optical detector located beneath a display and a detector electronics. The detector electronics includes an integrator configured to integrate an output from the detector, at least one counter which is connected to the integrator, and a memory which is connected to the integrator. The at least one counter is synchronized to a synchronization signal of the display. The at least one counter causes values to be periodically written from the integrator into the memory.
1 . An ambient light sensing system comprising an optical detector located beneath a display and detector electronics, wherein the detector electronics comprises:
an integrator configured to integrate an output from the optical detector;
at least one counter which is connected to the integrator; and
a memory which is connected to the integrator;
wherein the at least one counter is synchronized to a synchronization signal of the display, and wherein the at least one counter causes values to be periodically written from the integrator into the memory,
wherein the values periodically written from the integrator into the memory are obtained when pixels above the optical detector are not emitting light,
wherein additional values are periodically written from the integrator into the memory, the additional values being obtained at least partially when pixels above the optical detector are emitting light,
wherein the at least one counter causes values to be written into the memory which alternate between values obtained when pixels above the optical detector are not emitting light and values obtained at least partially when pixels above the detector are emitting light, and
wherein the at least one counter comprises one of:
a pair of counters, one counter providing an integration period corresponding with pixels above the detector not emitting light and the other counter providing an integration period during at least part of which pixels above the detector are emitting light, wherein the counters are configured to cause a value to be written from the integrator into the memory when each integration period ends, or
a single counter which is programmable with an integration period corresponding with pixels above the optical detector not emitting light and programmable with another integration period during at least part of which pixels above the optical detector are emitting light, wherein the counter is configured to cause a value to be written from the integrator into the memory when each integration period ends.
2 . The ambient light sensing system of claim 1 , further comprising a delay counter configured to delay, with respect to the synchronization signal, operation of the at least one counter, the delay depending upon a position of the optical detector beneath the display.
3 . The ambient light sensing system of claim 1 , wherein the at least one counter comprises a pair of counters, one counter providing an integration period corresponding with pixels above the detector not emitting light and the other counter providing an integration period during at least part of which pixels above the detector are emitting light, wherein the counters are configured to cause a value to be written from the integrator into the memory when each integration period ends.
4 . The ambient light sensing system of claim 3 , wherein each counter is configured to provide an output signal at the end of the integration period of that counter, and wherein the output signal from one of the counters is connected to the other counter and causes the integration period of the other counter to start.
5 . The ambient light sensing system of claim 3 , wherein the counters are programmable.
6 . The ambient light sensing system of claim 1 , wherein the at least one counter is a single counter which is programmable with an integration period corresponding with pixels above the optical detector not emitting light and programmable with an integration period during at least part of which pixels above the optical detector are emitting light, wherein the counter is configured to cause a value to be written from the integrator into the memory when each integration period ends.
7 . The ambient light sensing system of claim 5 , wherein when one of the integration periods ends the other integration period is programmed into the counter.
8 . The ambient light sensing system of claim 7 , wherein the integrator is reset after a predetermined number of integration periods.
9 . The ambient light sensing system of claim 1 , wherein the display is driven by a pulse width modulation signal, and wherein an integration period which provides a value to be written into the memory is equal to a low period of the pulse width modulation signal.
10 . The ambient light sensing system of claim 1 , wherein the display is driven by a pulse width modulation signal, and wherein an integration period which provides a value to be written into the memory is shorter than a low period of the pulse width modulation signal.
11 . The ambient light sensing system of claim 1 , wherein the system is configured to provide a continuous measurement.
12 . The ambient light sensing system of claim 1 , wherein the optical detector is a photodiode.
13 . A smartphone or tablet comprising a housing and a processor, and further comprising the ambient light sensing system of claim 1 .
14 . A method of measuring ambient light using an optical detector located beneath a display, the method comprising:
integrating an output from the detector over a first period of time;
when the first period of time ends, writing an integrator output value into a memory and starting a second period of time;
when the second period of time ends, writing an integrator output value into the memory and starting a new first period of time; and
continuing integration of the output detector for additional second and first periods of time in the same alternating manner to obtain and provide additional output values into the memory,
wherein the first periods of time correspond to when pixels above the optical detector are not emitting light,
wherein the second periods of time correspond to when pixels above the optical detector are emitting light, and
wherein the first and second periods of time are configured to be controlled by one of:
first and second counters counting the first and second periods of time respectively, or
a counter which is programmed to alternate between counting the first and second periods of time.
15 . The method of claim 14 , wherein the first and second periods of time are controlled by first and second counters.
16 . The method of claim 14 , wherein the first and second periods of time are controlled by a counter which is programmed to alternate between counting the first period and counting the second period.
17 . The method of claim 15 , wherein the first and second counters are programmed automatically by a pulse width modulation counter which monitors a pulse width modulation signal of the display.
18 . The method of claim 15 , wherein the first and second counters are programmed by a processor via a serial interface.
19 . The method of claim 15 , wherein a continuous measurement of light is provided.
20 . An ambient light sensing system comprising an optical detector located beneath a display and detector electronics, wherein the detector electronics comprises:
an integrator configured to integrate an output from the optical detector;
at least one counter which is connected to the integrator; and
a memory which is connected to the integrator;
wherein the at least one counter is synchronized to a synchronization signal of the display, and wherein the at least one counter causes values to be periodically written from the integrator into the memory,
wherein the values periodically written from the integrator into the memory are obtained when pixels above the optical detector are not emitting light,
wherein additional values are periodically written from the integrator into the memory, the additional values being obtained at least partially when pixels above the optical detector are emitting light,
wherein the at least one counter causes values to be written into the memory which alternate between values obtained when pixels above the optical detector are not emitting light and values obtained at least partially when pixels above the detector are emitting light, and
further comprising a delay counter configured to delay, with respect to the synchronization signal, operation of the at least one counter, the delay depending upon a position of the optical detector beneath the display.