Patent Application
20120001841
Many consumer electronic devices include displays such as liquid crystal displays or light emitting diode displays that implement some type of backlight source. In general, these displays can consume a great amount of power, particularly in the realm of portable devices such as cellular telephones, portable digital assistants, videogames and so forth. In addition, many of these same devices include a reflectance based proximity sensor.
To reduce power consumption in such devices, attempts are made to provide a detection mechanism to detect ambient light conditions to aid in determining an appropriate amount of illumination to be provided by the display based on an environment in which the display is located. Such a detector can be implemented using a high quality photodetector that is closely matched to a human photopic response. This optical processor can be integrated with a reflectance proximity sensor which can be used in many display applications to support various display and touch sensor inputs, enabling and disabling them as appropriate to reduce power and prevent spurious inputs (such as disabling the touch display when a cell phone is held to the head). Yet difficulties remain with available detectors.
According to one aspect of the present invention, a method for determining an ambient light type can be performed. The method includes receiving measurement information from multiple photodetectors configured for different light spectra, obtaining a correction value using a color ratio obtained from the measurement information, DC ambient level, and amplitude to DC of frequency components, applying the correction value to at least one of the measurement information to obtain a photopic illuminance value. Using this information, an ambient light type can be determined. Based on the ambient light type, one or more components of a system such as display of a portable device can be controlled accordingly.
Another aspect of the present invention is directed to an apparatus including multiple photodetectors to detect energy in different light spectra, and a controller to receive information from the photodetectors. The controller may calculate a color ratio between information from the first and second photodetectors, and determine an ambient light type present in a proximity of the apparatus based at least in part on the color ratio and measurement information and characteristics of the measurement information from one of the photo detectors. The controller may also perform an algorithm for calculating photopic illuminance value based on color ratio and ambient light type.
The apparatus can further include a multiplexer coupled to receive measurements from the photodetectors and to select for output a measurement, an amplifier to amplify the selected measurement, a comparator to compare the selected measurement to a threshold value, and a buffer coupled to the comparator to output a pulse width modulated signal representative of the comparator output. The apparatus, which may include a proximity detector having the photodetectors, can be included in various systems such as a portable device having a processor to perform application program instructions, a transceiver to transmit and receive radio frequency (RF) signals, a display to display information to a user, and the controller.
In various embodiments, a mechanism for determining a human-perceived brightness may be realized without using photodetectors (such as photodiodes) that are matched to a human eye response. Accordingly, using an embodiment of the present invention, inexpensive photodiodes may be used in an integrated circuit (IC) to provide improved performance with fewer design constraints. In addition, embodiments may further estimate an ambient light type present in a location of the IC.
In various embodiments, an IC may include multiple photodetectors, e.g., two photodiodes, neither of which are matched to a human eye photopic response curve. Such diodes may be configured to operate at different wavelengths. For example, in one embodiment, a first photodiode may be configured to have a response that peaks within a visible light spectrum and a second photodiode may be configured to have a response that peaks within an infrared light spectrum. Information from these two diodes may be used to determine a photopic illuminance value, i.e., a lux value, and an ambient light type. More specifically, using measurement information obtained from the diodes, a color ratio between the visible light and infrared light photodiodes can be calculated. Put another way, the measurement information provides a color ratio, i.e., a ratio between a signal strength of the detected energies, as represented by the visible light measurement and the infrared light measurement. A high color ratio indicates more visible blue weighted response relative to the infrared weighted response. It is noted that this color ratio may be influenced by the type of light present, as each light source includes a characteristic mix of infrared and visible light. For example, when an ambient light source is an incandescent light bulb, the color ratio is low, indicating that most of the light is in the infrared region, rather than in the visible region. If the light type is fluorescent or white LED, the color ratio will be highly weighted towards the visible light region. Thus, blackbody radiator light sources, such as incandescent or halogen lamps, can have significant energy in the infrared spectrum. On the other hand, fluorescent lamps have more energy in the visible light spectrum. The color ratio thus describes the relative strength of the visible photodiode reading relative to the infrared photodiode reading.
Based on the color ratio determination and other information, a correction value may be obtained. This correction value may be a value that acts to correct for the difference in response between a silicon photodiode and the human eye photopic response and thus may act to more closely match the photodiode outputs to a human eye photopic response curve. In one embodiment, this correction value may be based on collected characterization data, which may be data that are dynamically or statically obtained and preprogrammed into a device. For example, a lookup table may include information corresponding correction values with color ratios. Such correction values may be applied to at least one of the photodiode output values to obtain an approximate photopic illuminance lux value.
In addition to being based on color ratio, the ambient light type may further be a function of signal strength information and electrical waveform properties such as frequency components and AC to DC ratio. Embodiments thus may use signal strength information, frequency, AC to DC ratios, and/or color ratio to determine an ambient light type. Based on this information, an ambient light type in an environment which the IC is located can be determined. For example, based on the color ratio, frequency, AC to DC ratios, and signal strength, the ambient light type may be identified as direct sunlight (e.g., moderate color ratio, low AC, absolute strong DC signal), black body radiator light source (e.g., incandescent and halogen environments—low color, 100-120 Hz frequency component with a 10% peak to peak AC to DC value, small to moderate signal), or fluorescent (e.g., compact fluorescent light or white LED, high color ratio, combination of high frequency waveform from 40 KHz to 120 KHz at several percent peak to peak value with 100 Hz-120 Hz low frequency component, small to moderate signal).
Referring now to
As seen, package 105 includes an infrared emitter 103 which in one embodiment may be a light emitting diode (LED) that receives a signal from a semiconductor die 110 to enable transmission of an infrared signal out of first transparent window 106a. This emitter may be separated from the circuitry of die 110 by an optical block 108 such as a plastic barrier. Reflective infrared energy may be received through transparent window 106b by a photodetector 120, which in one embodiment may be an infrared-configured photodiode. In addition, another photodetector, namely photodetector 125 may receive incoming energy of the visible light spectrum. In one embodiment, photodetector 125 may be a photodiode configured for the visible light spectrum. These two photodiodes may employ different p-n junctions.
In one embodiment, visible light photodiode 125 peaks at around 530 nm. On the other hand, infrared photodiode 120 peaks at around 830 nm. Although the visible-light photodiode peaks near 550 nm (considered the peak wavelength of human perception), the visible photodiode extends to infrared light as well. Similarly, the infrared photodiode detects infrared light as well as part of the visible light spectrum. Note that the photodiodes may treat ultraviolet, visible, and infrared light as a continuous spectrum.
Various signal processing may be performed on die 110. Generally, incoming energy of both infrared and visible light spectra may be captured by the photodetectors and processed to generate output signals, which may be provided to another device such as a microcontroller or other control logic that can further process the information, e.g., to generate ambient light information such as ambient light type and proximity information. In general, the circuitry of die 110 may be controlled by a controller 160 which in one embodiment may be a mode controller. As seen, mode controller 160 is coupled to provide a selection signal to a multiplexer 130 which is configured to receive the outputs from the two photodetectors, which in one embodiment may be currents having a value based upon the received amount of energy. Multiplexer 130 may output the selected signal to an amplifier 135, which may amplify the current and provide it to a comparator 140. Comparator 140 may be configured to perform a comparison between this incoming signal and an output of a ramp generator 165 which in turn is controlled by controller 160. The ramp generator may output threshold values for the comparison based on the type of signal selected for processing by controller 160. The output of comparator 140 is a signal indicative of the measured amount of energy received in the corresponding photodetector. This information is buffered in a buffer 150 and output, e.g., as a pulse width modulated (PWM) signal. As will be discussed further below, the signal may be provided to an associated controller such as a microcontroller unit.
Note that controller 160 may further provide an output to a transmitter 170, which may output a current to drive infrared emitter 103. In one implementation, semiconductor die 110 may be fabricated using a CMOS process, although the scope of the present invention is not so limited. Further, while the detector of
As seen, control information may be sent from controller 210 to detector 100. Such control information may indicate a mode in which the detector is to operate, and may be sent to mode controller 160 (shown in
Referring now to
As seen in
R=Visible Photodiode Output/Infrared Photodiode Output.
In some embodiments, the IR detector may be configured at multiple wavelengths (e.g., a low and high IR spectrum) and a selected one of the resulting ratios may be used as described below.
Still referring to
Illuminance=(V−AV/R*IR)
where V=Visual photodiode output, IR=IR photodiode output, and AV/R is the correction factor from the look up table, where the inputs to access the table include the color ratio of V/IR, absolute IR level, frequency components and their peak-to-peak amplitudes.
In other embodiments, a dual approximation based on color ratio may occur. Specifically for a color ratio of visible light (VIS)/infrared (IR) an illuminance value may be determined as follows:
lux=(VIS−IR*k1)*k2 where VIS/IR>=th
lux=(VIS−IR*k3)*k4 where VIS/IR<th
where th is a threshold level, and k1-k4 are coefficient pairs. More specifically, the coefficients k1-k2 and k3-k4 pairs are two different linear approximations for improved ALS correction depending on color ratio; k2-k1 for one approximation and k3-k4 for the other. Having two different approximations may optimize the approximation based on light source type. In this embodiment, the type of light source can be identified based on color ratio (and/or waveform in general). Note that it is possible to generate more than two approximations and select the most appropriate (e.g., most accurate) based on color ratio and waveform properties.
In addition to this determination of an illuminance value, embodiments may further determine an ambient light type. More specifically, at block 350 an ambient light type may be determined based on the color ratio, the signal strength information which may be the compensated or uncompensated photodiode output of either of the photodiodes, and in some embodiments further based on the above-described characteristics. Note that not all of the above inputs are required for the correction table. Generally, color ratio and absolute level (which determines sunlight levels) if used as inputs to the table will result in less than 10% luminance error over standard white light sources.
While the above discussion is with regard to an implementation in which information from multiple photodetectors is used, in some embodiments it may be possible to use information from just a single photodetector to determine an ambient light condition as well as an approximate luminance value. One application for such an embodiment may be with regard to automatic light switches that enable or disable lighting operations based on whether some light is present. In these embodiments, information regarding the measurement taken from a single photodetector can be used, along with characteristics of the information such as frequency and amplitude. Based on all of this information an approximate lux value can be determined based on the photodiode output itself and a correction factor. This correction factor may be obtained from a table which is accessed based on the absolute level of the photodiode output and/or its frequency components. For example, if the absolute value is greater than a given threshold, a first correction factor may be used, while for measurements below this threshold, frequency information obtained from the measurement information may be used to access a correction factor. Thus an approximate lux value may be determined based on the photodiode output and this correction factor. Still further, using the approximate lux value, an ambient light determination may be made. From all of this information, e.g., for a smart light switch an approximate illumination value itself may be used to determine the presence of daylight such that the switch can be turned off.
Referring back to
The active modes can be set by clocking the state of MD and STX on the falling edge of SC and then setting MD to the given state. Since setting SC high forces shutdown, SC is held low for the selected mode to remain active. The timing diagram of
In proximity mode, an LED (e.g., LED 103 of
An offset calibration mode works the same way as the other proximity modes but without turning on the LED. This allows precise measurement of the environment and internal offsets without any LED light being reflected. The offset calibration mode also allows compensation of drifts due to supply and temperature changes.
Choosing between which color ratio to use depends on the light intensity. In general, a ratio that uses a low IR measurement (VAMB/VIRL) may be used if the signal strength of the IR detector is below a threshold level, since this measurement may have higher sensitivity. For higher light intensities (e.g., above the threshold level), a ratio that uses a high IR measurement (VAMB/VIRH) ratio may be used.
Note that VAMB, VIRH, and VIRL pulse widths are used as dividends and divisors in these ratios. The pulse width offsets (at 0 lux) may be removed prior to usage in the above color ratios. These offsets may be obtained by taking VAMB, VIRH, and VIRL measurements at 0 lux and using actual measured values. Or predetermined values (e.g., 7.1 μs, 11.3 μs, and 9.9 μs) may be removed respectively from VAMB, VIRH, and VIRL (then assigning 0 μs to any resulting negative value).
Because VAMB arises from a small photodiode, and also has low response and may have significant amplification, it has significant noise and variable offset. Below a certain light level, it is more accurate to use VIRL but correct it for its infrared level by multiplying its output by a coefficient dependent on the infrared component of the light source. The light source can be identified or the correct coefficient in the lookup table can be determined by the ratio of DC to AC and/or the frequency components in the signal.
Once a color ratio has been determined, the light type(s) and lux ratios are also identified. The lux ratio describes the ratio between the desired lux value and VAMB, VIRL, or VIRH (depending on the situation). The appropriate lux ratio, when multiplied with the applicable measurement, yields the final calculated lux value. Without any calibration, it should be possible to arrive within 50% (or 50 lux) of the absolute lux value.
Referring now to
Furthermore, as shown in
Thus one example of a proximity detection application is controlling the display and speaker of a portable device such as a cellular telephone. In this type of application, the cellular telephone turns off the power-consuming display and disables the loudspeaker when the device is next to the user's ear, then reenables the display (and, optionally, the loudspeaker) when the phone moves more than, e.g., a few inches away from the ear. However, the scope of the present invention is not so limited, and other examples of display control include enabling and disabling a touch display to prevent “ear” dialing.
While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.
