Patent Description:
A device may determine distances of its surroundings using different active depth sensing systems. In determining the depth, the device may generate a depth map illustrating or otherwise indicating the depths of objects from the device by emitting one or more wireless signals and measuring reflections of the wireless signals from the scene. One type of active depth sensing system is a time-of-flight (TOF) system. For an optical TOF system (such as a Light Detection and Ranging (LIDAR) sensor), a pulsed light is emitted, and a reflection of the pulsed light is received. The round trip time of the light from the transmitter to the receiver is determined from the pulses, and the distance or depth between an object reflecting the emitted light and the TOF system is determined from the round trip time.

<CIT> describes photodetectors to convert detected light, reflected from a three-dimensional object, into electrical charges. Each photodetector includes two groups of switches that collect the electrical charges. The collection of the electrical charges by two groups of switches that may be altered over time, such that the imaging system may determine phase information of the sensed light. The photodetector may be a switched photodetector configured for time-of-flight detection. The photodetector may include a light absorption region including germanium.

<CIT> describes a lidar system operating in a vehicle.

The invention is defined in the appended independent claims, particularly by the apparatus set out in claim <NUM> and by the method set out in claim <NUM>. Optional features are defined in the dependent claims.

Aspects of the present disclosure are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements.

Aspects of the present disclosure may be used for active depth sensing systems, such as a TOF system. TOF systems are used in determining depths, and are found in many applications today, including radio detection and ranging (RADAR), sound navigation and ranging (SONAR), and light detection and ranging (LIDAR). For example, many autonomous vehicles (such as unmanned aerial vehicles (UAVs) and autonomous cars) include one or more LIDAR systems, and the LIDAR systems are used in the detection of obstacles for vehicle guidance.

An optical TOF system may emit and receive reflections of light. Many optical TOF systems, such as some LIDAR systems, may use near-infrared (NIR) light. In some implementations, NIR light may be defined as having a wavelength from <NUM> nanometers to <NUM> nanometers. For example, a LIDAR system may use <NUM> nanometer or <NUM> nanometer wavelength light. An optical TOF system includes one or more photodetectors to receive reflections of emitted light from a transmitter of the TOF system. However, when a TOF system uses light having an <NUM> nanometer or <NUM> nanometer wavelength, reflections of the emitted light may be obscured by ambient light and interference. For example, the sun emits a majority of energy with a wavelength below <NUM> nanometers (such as visible light and infrared light with a sub-<NUM> nanometer wavelength). As a result, reflections as received by a photodetector may be obscured in bright sunlight, and TOF systems may have difficulty in accurately determining depths.

To reduce interference caused by background radiation (such as sunlight), an optical TOF system may use a signal with a wavelength greater than <NUM> nanometers (or greater than <NUM> nanometers). For example, an optical TOF system may emit light having an approximate <NUM> nanometer wavelength (or other wavelength with less interference from ambient light than <NUM> nanometers or <NUM> nanometers). The photosensitive surface of a photodetector, which is configured to absorb photons to provide a current, may be silicon. Silicon loses efficiency in absorbing photons as the wavelength increases above <NUM> nanometers. For example, a silicon-based photosensitive surface photodiode is more efficient in absorbing <NUM> to <NUM> nanometer wavelength light than in absorbing <NUM> to <NUM> (or greater) nanometer light. Indeed, a silicon-based photosensitive surface may be unable to absorb light with a wavelength greater than <NUM> nanometers.

In some implementations, an image sensor may include one or more photodiodes with a different compound than pure silicon for its photosensitive surface. The compound may be configured to absorb light at least with wavelengths greater than <NUM> nanometers. For example, a photodiode may have a photosensitive surface including a silicon germanium compound to increase the absorption efficiency by the photodiode of light with a wavelength greater than <NUM> nanometers. In another example, the photodiode may have a photosensitive surface including germanium crystals without silicon to increase the absorption efficiency by the photodiode of light with a wavelength greater than <NUM> nanometers. In this manner, an optical TOF system may use light with a wavelength greater than <NUM> nanometers (or <NUM> nanometers) for depth sensing.

One advantage of using higher wavelength light is that the TOF system is less impacted by ambient light and interference, which increases the signal to noise ratio of the sensed light at the photodiode and the effective range of the TOF system. Another advantage of using light with a wavelength greater than <NUM> nanometers is that such light is considered safer for eyes than sub-<NUM> nanometer wavelength light (which may be received at the retina and damage the eye). For example, light that may be considered a retinal hazard may have a wavelength in the range of <NUM> nanometers (ultraviolet light) to <NUM> nanometers (which may be SWIR light). Light within such range may be limited in intensity as a result of eye safety concerns. However, the intensity of emitted light with a wavelength greater than <NUM> nanometers may be safely increased over the intensity of, for example, <NUM> nanometer wavelength light for a TOF system because the higher wavelength light would not be absorbed by a retina and cause damage. Increasing the light intensity increases the signal to noise ratio of the sensed light at the photodiode, which may increase the effective range of the TOF system and the quality of the data. Various aspects of a photodetector and image sensor for a TOF system are described herein. While the examples are provided regarding infrared light (such as greater than <NUM> nanometer wavelength light, greater than <NUM> nanometer wavelength light, <NUM> nanometer wavelength light, and <NUM> nanometer wavelength light), any suitable frequency spectrum signals may be used for the TOF system. The light may be in the visible light spectrum (such as visible to the naked eye) or the light may be outside the visible light spectrum (such as ultraviolet and infrared light). Additionally, any suitable infrared light may be used, including NIR, short-wave infrared (SWIR), and far-infrared (FIR). In some implementations, SWIR may refer to wavelengths between <NUM> nanometers and <NUM> nanometers. Infrared may also refer to light in the visible light spectrum and outside the visible light spectrum. As such, the disclosure is not limited to the provided examples of wavelengths for the emitted light.

A TOF system may be a direct TOF system or an indirect TOF system. A direct TOF system emits pulses, senses the pulses, and determines a difference in time between emitting a pulse and sensing a reflection of the pulse. The direct TOF system uses the time difference to determine a round trip time, and thus a depth of an object from the TOF system.

<FIG> is a depiction of an example direct TOF system <NUM>. The direct TOF system <NUM> includes a transmitter <NUM> and a receiver <NUM>. The transmitter <NUM> may also be referred to as a "projector" or an "emitter," and is not limited to a specific transmission component. The receiver <NUM> may be referred to as a "detector," "sensor," "sensing element," or "photodetector," and is not limited to a specific receiving component.

The transmitter <NUM> may be configured to emit signals (such as light <NUM>) toward a scene including surface <NUM>. While the emitted light <NUM> is illustrated as being directed to surface <NUM>, the field of the emission by the transmitter <NUM> may extend beyond the size of the surface <NUM>. For example, a TOF system transmitter may have a fixed focal length lens that defines the field of the emission for the transmitter.

The emitted light <NUM> includes light pulses <NUM> at known time intervals (such as a defined period). The receiver <NUM> includes an image sensor <NUM> to sense the reflections <NUM> of the emitted light <NUM>. The reflections <NUM> include the reflected light pulses <NUM>, and the TOF system determines a round trip time <NUM> for the light by comparing the timing <NUM> of the emitted light pulses <NUM> to the timing <NUM> of the reflected light pulses <NUM>. The distance of the surface <NUM> from the TOF system may be calculated to be half the round trip time multiplied by the speed of the emissions (such as the speed of light for light emissions). The depth may be determined using equation (<NUM>) below: <MAT> where D is the depth of the surface <NUM> from the direct TOF system <NUM> and c is the speed of light (based on the transmitter <NUM> emitting light <NUM>).

The image sensor <NUM> may include an array of photodiodes and components to sense the reflections and produce an array of currents or voltages corresponding to the intensities of the light received. Each entry in the array may be referred to as a pixel or cell. The TOF system may compare voltages (or currents) from a pixel over time to detect reflections <NUM> of the emitted light <NUM>. For example, the TOF system may compare the signal to a threshold (corresponding to noise, such as ambient light), and the TOF system may identify peaks greater than the threshold as reflected light pulses <NUM> sensed by the image sensor <NUM>. The threshold may be based on ambient light or other interference. For example, an amount of ambient light may exist (without the emitted light <NUM>), and the threshold may be based on the magnitude of ambient light (such as measured by the image sensor <NUM>). The upper limit of the effective range of a TOF system may be the distance where the noise or the degradation of the signal before sensing the reflections cause the signal-to-noise ratio (SNR) to be too great for the sensor to accurately sense the reflected light pulses <NUM>. To reduce interference (and thus increase range or improve the signal to noise ratio), the receiver <NUM> may include a bandpass filter before the image sensor <NUM> to filter incoming light outside of a wavelength range than the emitted light <NUM>.

Direct TOF systems may be susceptible to interference, such as ambient light or other noise that may obscure pulses in the reflections received at the image sensor <NUM>. As a result, each pixel of an image sensor <NUM> of a direct TOF system may include a single-photon avalanche diode (SPAD) due to its sensitivity and responsivity to enable identifying pulses in the reflections and resolving the arrival time of pulsed light reflections. However, SPAD-based depth sensing suffers from a trade-off between spatial resolution and background light rejection capability. Increasing spatial resolution decreases the ability to differentiate pulses from ambient light. In addition, the area required for readout circuits of the SPADs, time-correlated time-to-digital converters (TDCs) and memory cells of the image sensor <NUM> reduces available space for other components of the direct TOF system or other systems.

Another TOF system is an indirect TOF system (which may also be referred to as a Frequency Modulated Continuous Wave (FMCW) TOF system). An indirect TOF system emits a periodic signal (such as a continuous wave sinusoidal signal or periodic pulsed light), senses a reflection of the signal, and determines a phase difference between the emitted signal and the sensed reflection of the signal. The indirect TOF system uses the phase difference to determine a depth of an object from the TOF system.

<FIG> is a depiction of an example indirect TOF system <NUM>. The indirect TOF system <NUM> includes a transmitter <NUM> and a receiver <NUM>. The transmitter <NUM> may be configured to emit signals (such as light <NUM>) toward a scene including surface <NUM>. While the emitted light <NUM> is illustrated as being directed to surface <NUM>, the field of the emission by the transmitter <NUM> may extend beyond the size of the surface <NUM>. For example, a TOF system transmitter may have a fixed focal length lens that defines the field of the emission for the transmitter.

The emitted light <NUM> includes a sinusoidal signal <NUM> (or other suitable periodic signal) of a defined frequency. The receiver <NUM> includes an image sensor <NUM> to sense the reflections <NUM> of the emitted light <NUM>. The reflections <NUM> include the reflected sinusoidal signal <NUM>. The indirect TOF system <NUM> determines a phase difference <NUM> between the emitted sinusoidal signal <NUM> and the reflected sinusoidal signal <NUM> (as illustrated by emitted sinusoid timing <NUM> and reflected sinusoid timing <NUM>). The phase difference <NUM> may indicate a round trip time and thus may be used to determine the distance of the surface <NUM> from the indirect TOF system. To produce the sinusoidal signal <NUM>, the TOF system <NUM> may be configured to modulate a carrier signal to produce the sinusoid wave. For example, a <NUM> nanometer wavelength light may be modulated to create the sinusoidal signal <NUM>. The frequency of the wave may be referred to herein as a modulation frequency. In comparing the relationship of TOF and phase difference, the TOF may be defined in terms of the measured phase difference (PD) and the modulation frequency (fmod), as depicted in equation (<NUM>) below: <MAT> In a simplified example, if the PD is π and fmod is approximately <NUM> kilohertz (kHz), the TOF is <NUM> microseconds (<NUM> divided by <NUM>). Referring back to equation (<NUM>), the depth D based on the TOF equaling <NUM> microseconds is approximately <NUM> meters.

While <FIG> illustrates the emitted signal as having a sinusoidal waveform, any suitable waveform may be used. For example, the TOF system may be configured to stepwise increase and decrease the intensity of the emitted light in a periodic pattern. In this manner, the waveform of the emitted light may approximate a square wave (such as for a periodic pulsed signal). Other waveforms may be used, including a saw waveform and so on. As used herein, a sinusoid waveform or wave may refer to any suitable waveform for the signals (including an approximated square wave).

In some implementations, the indirect TOF system <NUM> may include a demodulation circuit for each pixel of the image sensor <NUM> (referred to herein as a demodulation pixel or a lock-in pixel). Each demodulation pixel may include a demodulation photodetector and be configured to generate and store one or more voltages corresponding to a phase or phase difference of the reflected sinusoidal signal received at the photodiode of the array and the emitted sinusoidal signal. The phase difference may be determined from the one or more stored voltages. For example, a demodulation pixel may generate a voltage signal (such as using a current from a photodiode to determine whether to send a pixel voltage (such as a rail voltage) or a low voltage as the voltage signal). An example image sensor <NUM>, using the demodulation pixels, may generate an array of voltages for a single capture by the image sensor <NUM>. The array of voltages may be processed to generate a PD for each pixel. <FIG> illustrates an example indirect TOF image sensor, and <FIG> illustrates a demodulation pixel of an example image sensor.

<FIG> is a depiction of an indirect TOF image sensor <NUM>. The image sensor <NUM> may be an example implementation of the image sensor <NUM> in <FIG>. The image sensor <NUM> includes an array <NUM> of pixels <NUM>, column amplifiers <NUM>, a column comparator <NUM>, a column counter <NUM>, a column multiplexer (MUX) <NUM>, a digital controller <NUM>, a transmit (TX) delay controller <NUM>, a TX driver / row controller <NUM>, a reference signal / ramp generator <NUM>, and a bias circuit <NUM>. The array <NUM> may be of size M rows by N columns of pixels <NUM>. In some implementations, the array <NUM> may be <NUM> x <NUM> pixels in size. Each pixel <NUM> may include a demodulation pixel. The pixels <NUM> may be arranged such that the array includes a <NUM> micrometer x <NUM> micrometer pitch. In some other implementations, the pitch may be <NUM> micrometers x <NUM> micrometers (such as for a <NUM> x <NUM> pixel array <NUM>).

The image sensor <NUM> may be configured to drive pixel rows of the array for absorbing photons and generating a voltage corresponding to the photons absorbed. For example, the TX driver / row controller <NUM> may receive a signal from a digital controller <NUM>, and provide a signal to one or more of the rows of the array <NUM> to drive those pixels <NUM> for readout from the array <NUM>. The driven pixels <NUM> may provide the stored voltages to the column amplifiers <NUM>, which amplify the received signals from the driven row of pixels <NUM>. The amplified signals are provided to the column comparator <NUM>, the column counter / latch <NUM> and the column MUX <NUM> for processing before being output by the image sensor <NUM>. The digital controller <NUM> may be configured to control operation of the comparator <NUM>, counters <NUM> and MUX <NUM>.

The column comparator <NUM> may be configured to compare the amplified signals from the pixels <NUM> to a threshold voltage to determine a value for the voltage from the pixel <NUM>. For example, the reference / ramp generator <NUM> may provide a ramp voltage to the comparator <NUM> for each readout from the array <NUM>. If the ramp voltage is ascending, the comparator may compare the received voltage from the pixel <NUM> to the ramp voltage until the ramp voltage is greater than the voltage from the pixel <NUM>. In this manner, the comparator <NUM> may convert the voltage from the pixel <NUM> to a value corresponding to the ramp voltage when the two voltage levels cross each other. The values may be provided to the counter <NUM> to add the values over multiple readouts, and the added value may be provided to the MUX <NUM> at a determined time. The MUX <NUM> may then combine the values for output from the image sensor <NUM>, and the output may be used by the TOF system (such as a signal processor or controller)to determine a depth of an object from a corresponding pixel <NUM> of the image sensor <NUM>.

The TOF emitter may have a delay in emitting the modulated light. The image sensor <NUM> may be configured to delay driving the rows of the array <NUM> to compensate for the delay. For example, the digital controller <NUM> may control the TX delay controller <NUM> to delay the TX driver / row controller <NUM> from driving one or more rows of the array <NUM> for amount of time corresponding to the delay.

The intensity of the emitted light decreases as it travels through the scene and is reflected by one or more objects. As a result, the intensity of the reflected light received at the image sensor <NUM> is less than the intensity of the emitted light at the transmitter of the TOF system. To compensate, the image sensor <NUM> may combine a bias voltage with the voltages from the pixels <NUM>. For example, the reference / ramp generator <NUM> may provide a reference signal (such as a bias current) to the bias circuit <NUM>, and the bias circuit <NUM> may convert the reference signal to a bias voltage applied to the columns of the array <NUM>.

As noted above, each pixel <NUM> may be a demodulation pixel. A demodulation pixel may sample multiple times per wavelength to prevent ambiguity in determining the phase of the reflected signal (since a value may occur two times within a π wavelength of a sinusoid wave). For example, a <NUM>-phase demodulation pixel may sample two times every wavelength (such as at <NUM> and π), a <NUM>-phase demodulation pixel may sample three times every wavelength (such as at <NUM>, <NUM>/<NUM>π, and <NUM>/<NUM>π), and a <NUM>-phase demodulation pixel may sample four times every wavelength (such as at <NUM>, <NUM>/<NUM>π, π, and <NUM>/<NUM>π).

<FIG> is a depiction of a demodulation pixel <NUM> of an indirect TOF system. The demodulation pixel <NUM> is an example of a <NUM>-phase demodulation pixel. The demodulation pixel <NUM> may be an implementation of a demodulation pixel of the image sensor <NUM> in <FIG>. The demodulation pixel <NUM> may be illustrated in a simplified form to explain aspects of the pixel. For example, while not shown, the demodulation pixel <NUM> may include one or more read out lines, filtering components, voltage rails, reset switches, and other components.

The demodulation pixel <NUM> includes a photodiode <NUM>, a first transistor <NUM>, a second transistor <NUM>, a first capacitor <NUM>, and a second capacitor <NUM>. The photodiode <NUM> is configured to convert received light (including the reflected light from the emitter and ambient light) to a current. If the pixel <NUM> samples during the first half of a phase of the reflected signal (such as when the reflected sinusoidal signal has a phase of <NUM>/<NUM>π), the current may be higher that if sampled during the second half of the phase.

The first transistor <NUM> is configured to receive the current from the photodiode <NUM> and output a voltage V1 to be stored in capacitor <NUM> based on the current. In some implementations, the voltage V1 may be a voltage from a voltage rail (not shown) of the demodulation pixel <NUM> when the current from the photodiode <NUM> is high and the first transistor <NUM> is closed. Operation of the first transistor <NUM> is controlled by a representation of the emitted signal <NUM>. In this manner, the transistor <NUM> may enable the capacitor <NUM> when the phase of the emitted signal <NUM> is between <NUM> and π, and the transistor <NUM> may disable the capacitor <NUM> when the phase of the emitted signal <NUM> is between π and 2π. As used herein for a demodulation pixel, the emitted signal may be a voltage signal with a frequency corresponding to the modulation frequency of the emitted light.

The second transistor <NUM> is configured to receive the current from the photodiode <NUM> and output a voltage V2 to be stored in capacitor <NUM>. In some implementations, the voltage V2 may be a voltage from a voltage rail (not shown) of the demodulation pixel <NUM> when the current from the photodiode <NUM> is high and the second transistor <NUM> is closed. Operation of the second transistor <NUM> is controlled by a representation of the inverted emitted signal <NUM> (such as the emitted signal <NUM> shifted by π). In this manner, the transistor <NUM> may disable the capacitor <NUM> when the phase of the inverted emitted signal <NUM> is between <NUM> and π, and the transistor <NUM> may enable the capacitor <NUM> when the phase of the inverted emitted signal <NUM> is between π and 2π. Voltages V1 and V2 can be read out and compared to determine the phase difference between the reflected signal and the emitted signal. For example, if V1 switches from low to high when the emitted signal <NUM> is high, the phase difference may be between <NUM> and π. If V2 switches from low to high when the inverse emitted signal <NUM> is high, the phase difference may be between π and 2π. The demodulation pixel <NUM> may include additional transistor and capacitor pairs (not shown) to increase the number of phases for sampling. For an example <NUM>-phase demodulation pixel, one additional transistor and capacitor pair may be coupled to the photodiode <NUM> (similar to the transistors <NUM> and <NUM>), and the transistors may be controlled by the emitted signal with different phase offsets (such as the emitted signal <NUM>, <NUM>/<NUM>π phase offset from the emitted signal <NUM>, and <NUM>/<NUM>π phase offset from the emitted signal <NUM>). For an example <NUM>-phase demodulation pixel, two additional transistor and capacitor pairs may be coupled to the photodiode <NUM> (similar to the transistors <NUM> and <NUM>), and the transistors may be controlled by the emitted signal with different phase offsets (such as the emitted signal <NUM>, <NUM>/<NUM>π phase offset from the emitted signal <NUM>, π phase offset from the emitted signal <NUM>, and <NUM>/<NUM>π phase offset from the emitted signal <NUM>). An implementation of a <NUM>-phase demodulation pixel is illustrated in <FIG>, an implementation of a <NUM>-phase demodulation pixel is illustrated in <FIG>, and an implementation of a <NUM>-phase demodulation pixel is illustrated in <FIG>.

<FIG> is a depiction of an implementation of a <NUM>-phase demodulation pixel <NUM>. The demodulation pixel <NUM> may be an implementation of the demodulation pixel <NUM> in <FIG>. The demodulation pixel <NUM> includes a photodiode <NUM>, a first phase sampling circuit <NUM>, and a second phase sampling circuit <NUM>. In some implementations, the first phase sampling circuit <NUM> may have the same configuration as the second phase sampling circuit <NUM>. The difference between the first phase sampling circuit <NUM> and the second phase sampling circuit <NUM> may be Tap <NUM> receiving an emitted signal with a first phase offset (such as <NUM> phase offset) to enable the circuit <NUM> and Tap <NUM> receiving an emitted signal with a second phase offset (such as π phase offset) to enable the circuit <NUM>. In some implementations, higher phase demodulation pixels (such as a <NUM>-phase demodulation pixel or a <NUM>-phase demodulation pixel) may include additional sampling circuits.

<FIG> is a depiction of an implementation of a <NUM>-phase demodulation pixel <NUM>. The <NUM>-phase demodulation pixel <NUM> includes a photodiode <NUM>, a first sampling circuit <NUM>, a second sampling circuit <NUM>, and a third sampling circuit <NUM>. The <NUM>-phase demodulation pixel <NUM> may be similar to the <NUM>-phase demodulation pixel <NUM> in <FIG>, except that the <NUM>-phase demodulation pixel <NUM> includes an additional sampling circuit <NUM>. The third sampling circuit <NUM> may be enabled based on the tap <NUM> receiving the emitted signal with the third phase offset. In this manner, sampling by the three sampling circuits <NUM>, <NUM>, and <NUM> may be performed for different phase offsets of the emitted signal.

<FIG> is a depiction of an implementation of a <NUM>-phase demodulation pixel <NUM>. The <NUM>-phase demodulation pixel <NUM> includes a photodiode <NUM>, a first sampling circuit <NUM>, a second sampling circuit <NUM>, a third sampling circuit <NUM>, and a fourth sampling circuit <NUM>. The <NUM>-phase demodulation pixel <NUM> may be similar to the <NUM>-phase demodulation pixel <NUM> in <FIG>, except that the <NUM>-phase demodulation pixel <NUM> includes an additional sampling circuit <NUM>. The fourth sampling circuit <NUM> may be enabled based on the tap <NUM> receiving the emitted signal with the fourth phase offset. In this manner, sampling by the four sampling circuits <NUM>, <NUM>, <NUM>, and <NUM> may be performed for different phase offsets of the emitted signal (such as <NUM>, <NUM>/<NUM>π, π, and <NUM>/<NUM>π). While evenly spaced phase offsets are described in some of the examples, any suitable phase offsets (and spacing of such phase offsets) may be used.

Each of the photodiodes <NUM>, <NUM>, and <NUM> in <FIG>, respectively, are coupled to the corresponding sampling circuits of the demodulation pixel. A photodiode of a demodulation pixel may provide, to each of the sampling circuits, a current corresponding to the photons received at a photosensitive surface of the photodiode. As noted above, a photodetector (such as a photodiode) having a pure silicon photosensitive surface may inefficiently absorb photons to generate a current when the wavelength of the light received at the photosensitive surface is greater than <NUM> nanometers. In some implementations, a photodetector may include a photosensitive surface including a non-silicon element to improve the absorption of light having a wavelength greater than <NUM> nanometers. For example, a p-i-n photodiode may include a photosensitive intrinsic layer that is not purely silicon. In some implementations, the photosensitive surface may include germanium. For example, the intrinsic layer of a p-i-n photodiode may include a combination of silicon and germanium. In some other implementations, the photosensitive surface may be crystalline germanium. For example, if the wavelength of the emitted light to be received is greater than <NUM> nanometers, the intrinsic layer of a photodiode may be crystalline germanium without silicon or other elements.

<FIG> is a depiction of a portion of a circuit <NUM> including a photodiode <NUM> configured to be coupled to one or more sampling circuits. As depicted, the photodiode <NUM> is a vertical p-i-n photodiode including a p- doped region <NUM>, an n-doped region <NUM>, and an intrinsic region <NUM> between regions <NUM> and <NUM>. In some implementations, two contacts from a metal <NUM> (M1) layer may be coupled to the photodiode <NUM> to control operation.

For a p-i-n photodiode <NUM>, the intrinsic layer <NUM> may be exposed to incoming light (at the demodulation pixel), and the intrinsic layer <NUM> is configured to absorb the received photons to cause the photodiode <NUM> to generate a current to the n- well in a p epitaxial layer <NUM> on a substrate <NUM> of a silicon chip. When the transmit (TX) field effect transistor (FET) <NUM> is enabled, the current from the photodiode <NUM> is provided to contact <NUM> via an n+ well. The n+ well may store a floating charge from the photodiode <NUM> when the contact <NUM> is open. Contact <NUM> may be coupled to the one or more sampling circuits (such as depicted in <FIG>), and the current from the photodiode <NUM> may be provided to the sampling circuit when the sampling circuit is enabled.

The circuit <NUM> may also include a contact <NUM> for resetting the charge from the photodiode <NUM>. The reset signal may enable the reset (RST) FET <NUM> to drain the floating charge from the n+ well coupled to the contact <NUM> to the other n+ well. As shown, the n+ wells may be included in a p- well. To isolate the portion of the silicon chip corresponding to the photodiode <NUM> from other components (such as to prevent parasitic interference or leaching), the p- wells may include shallow trench insulators (STIs). As illustrated, one or more contacts (such as contacts <NUM> and <NUM>, or the contacts coupled to the photodiode <NUM>) may be coupled to one or more metal layers of the circuit (such as the M1 layer and/or the metal <NUM> (M2) layer).

As noted, <FIG> depicts a vertical p-i-n photodiode <NUM> where the layers are stacked vertically. In some other implementations, a photodiode may be a horizontal p-i-n photodiode. For a horizontal p-i-n photodiode, the layers are stacked horizontally.

<FIG> is a depiction of a portion of a circuit <NUM> including a horizontal p-i-n photodiode <NUM> configured to be coupled to one or more sampling circuits. As shown, the circuit and silicon chip configuration may be the same for the photodiode <NUM> and the photodiode <NUM> in <FIG>. The photodiode <NUM> includes a p- doped region <NUM>, an intrinsic region <NUM>, and an n- doped <NUM> stacked horizontally. The intrinsic layer <NUM> is exposed to the light received at the demodulation pixel, and the intrinsic layer <NUM> is configured to absorb the received photons to cause the photodiode <NUM> to provide a current to the n- well.

To increase absorption at the intrinsic region <NUM> (in <FIG>) and <NUM> for higher wavelength light than <NUM> nanometers or <NUM> nanometers (such as greater than <NUM> nanometer wavelength light), the material of the intrinsic layer may include an element in addition to, or alternative to, silicon. For example, the material may be a silicon germanium compound. In some implementations, during manufacture of the photodiode, the intrinsic region may be silicon that is doped with germanium. In another example, the material may be a crystalline germanium.

<FIG> is a depiction of a vertical p-i-n photodiode <NUM>. The vertical p-i-n photodiode <NUM> may be an implementation of photodiode <NUM> in <FIG>. The photodiode <NUM> includes a p- layer <NUM>, an n- layer <NUM>, and an intrinsic layer <NUM> stacked vertically. The intrinsic layer <NUM> includes silicon doped with germanium or an exclusively germanium material (as indicated by the depicted atomic structure Si<NUM>-xGex where x is greater than <NUM> and x is less than or equal to <NUM>). In some implementations, the p- layer <NUM> and the n- layer <NUM> are not doped with germanium or otherwise include germanium. In this manner, the germanium intrinsic layer <NUM> is between silicon layers without germanium. <FIG> is a depiction of a horizontal p-i-n photodiode <NUM>. The photodiode <NUM> includes a p- layer <NUM>, an n-layer <NUM>, and an intrinsic layer <NUM> stacked horizontally. The horizontal p-i-n photodiode <NUM> may be an implementation of photodiode <NUM> in <FIG>. The intrinsic layer <NUM> includes silicon doped with germanium or an exclusively germanium material (as indicated by the depicted atomic structure Si<NUM>-xGex where x is greater than <NUM> and x is less than or equal to <NUM>). In some implementations, the p- layer <NUM> and the n-layer <NUM> are not doped with germanium or otherwise include germanium. In this manner, the germanium intrinsic layer <NUM> is between silicon layers without germanium. For germanium doped silicon, the amount of germanium doped into the silicon may be any suitable amount such that the ratio of silicon atoms to germanium atoms may be any suitable ratio. In some other implementations, the intrinsic layer may be a material excluding silicon (such as germanium or germanium doped with another element). Through the introduction of another element (such as germanium), the photodiode is able to more efficiently absorb photons from light with a wavelength greater than <NUM> nanometers (such as a wavelength of <NUM> to <NUM> nanometers for germanium doped silicon in the photodiode or a wavelength of greater than <NUM> nanometers for crystalline germanium in the photodiode).

An image sensor may include, for one or more pixels, a photodetector having a photosensitive surface including germanium. For example, each demodulation pixel of an image sensor array may include a photodiode, and the photodiode may include an intrinsic layer of silicon doped with germanium (or pure germanium without silicon). While the examples are described regarding a germanium doped silicon photosensitive region, the examples also apply to other materials, including germanium crystals (as described herein).

The image sensor may be included in a receiver for active depth sensing. For example, the image sensor may be included in a receiver of a TOF system (such as an indirect TOF system) for determining a depth of one or more objects' surfaces from the TOF system. The demodulation pixel may be any suitable configuration to determine a phase difference between light emitted by an indirect TOF system's emitter and reflections of the light received at the indirect TOF system's receiver. For example, the demodulation circuit may be a <NUM>-phase demodulation circuit, a <NUM>-phase demodulation circuit, a <NUM>-phase demodulation circuit, or another suitable phase demodulation circuit. The demodulation circuit may include filtering or processing components (such as for background light cancellation or reduction, wave drift compensation, and so on).

The active depth sensing system (such as an indirect TOF system) including the image sensor may be included in any suitable device. For example, the image sensor including one or more demodulation pixels having a germanium doped intrinsic layer photodiode may be included in a LIDAR system coupled to a vehicle (such as a car or UAV) for autonomous operation of the vehicle. In another example, the image sensor may be included in a wireless communication device (such as a smartphone, tablet, and so on). In a further example, the image sensor may be included in a handheld device (such as a digital camera, a range finder, and so on). The image sensor may be included in any suitable device for active depth sensing.

<FIG> is a block diagram of an example device <NUM>. The example device <NUM> may include an active depth sensing system. In some other examples, the active depth sensing system may be coupled to the device <NUM>. The example device <NUM> may include a transmitter <NUM>, a receiver <NUM>, a processor <NUM>, a memory <NUM> storing instructions <NUM>, and a controller <NUM> (which may include one or more signal processors <NUM>). The device <NUM> may optionally include (or be coupled to) a display <NUM> and a number of input/output (I/O) components <NUM>. The device <NUM> may include additional features or components not shown. For example, the device <NUM> may include a wireless interface, which may include a number of transceivers and a baseband processor for wireless communication. The device <NUM> may also include a power supply <NUM>, which may be coupled to or integrated into the device <NUM>.

The transmitter <NUM> and the receiver <NUM> may be part of an active depth sensing system. For example, the transmitter <NUM> may be a transmitter <NUM> and the receiver <NUM> may be a receiver <NUM> of an indirect TOF system <NUM> in <FIG>. The active depth sensing system may be controlled by the controller <NUM> (such as signal processor <NUM>) and/or the processor <NUM>. The transmitter <NUM> may include or be coupled to one or more power sources for adjusting a power to cause pulses or modulation of an emitted light. The receiver <NUM> may be configured to receive reflections of the emitted light from the transmitter <NUM>.

The receiver <NUM> may include one or more image sensors including a photodetector with a photosensitive surface including germanium. For example, the receiver <NUM> may include an image sensor having an array of pixels, and each pixel may include a demodulation circuit having p-i-n photodiode with a germanium doped intrinsic layer. In some implementations, the photosensitive surface of a photodetector of a pixel may have a normal incidence for receiving light (the angle of incidence being <NUM>).

While the active depth sensing system is depicted as including one receiver and one image sensor, any number of receivers or image sensors may be included in the active depth sensing system. For example, the active depth sensing system may include multiple image sensors for light sensing from different perspectives. Additionally, while the device <NUM> is depicted as including one active depth sensing system, the device <NUM> may include or be coupled to additional active depth sensing systems, and the disclosure is not limited to a device including one active depth sensing system. In some other implementations, the active depth sensing system may be a structured light system, and the transmitter <NUM> and the receiver <NUM> may be separated by a baseline for performing depth sensing.

The memory <NUM> may be a non-transient or non-transitory computer readable medium storing computer-executable instructions <NUM> to perform all or a portion of one or more device operations. The processor <NUM> may be one or more suitable processors capable of executing scripts or instructions of one or more software programs (such as instructions <NUM>) stored within the memory <NUM>. In some aspects, the processor <NUM> may be one or more general purpose processors that execute instructions <NUM> to cause the device <NUM> to perform any number of functions or operations. In additional or alternative aspects, the processor <NUM> may include integrated circuits or other hardware to perform functions or operations without the use of software. For example, a TOF system may be a LIDAR system, and the device <NUM> may be an apparatus for controlling navigation of a vehicle (such as a car or a UAV). A processor <NUM> may execute instructions <NUM> to cause the device <NUM> to control navigation of the vehicle (such as speed, steering, acceleration, altitude, and so on) based on depth sensing from the active depth sensing system. The device <NUM> may also be configured to alert a user (such as a driver or UAV operator) of obstacles or other events based on the depth sensing.

While shown to be coupled to each other via the processor <NUM> in the example of <FIG>, the processor <NUM>, the memory <NUM>, the controller <NUM>, the optional display <NUM>, and the optional I/O components <NUM> may be coupled to one another in various arrangements. For example, the processor <NUM>, the memory <NUM>, the controller <NUM>, the optional display <NUM>, and the optional I/O components <NUM> may be coupled to each other via one or more local buses (not shown for simplicity).

The display <NUM> may be any suitable display or screen allowing for user interaction and/or to present items to a user (such as a depth map, a preview image of the scene, an alert, and so on). In some aspects, the display <NUM> may be a touch-sensitive display. In some examples, the display <NUM> may be a heads up display or center console display in an automobile, the display <NUM> may be a display of a smartphone, digital camera, or other electronic device, or the display may be a display on a user controller for UAV.

The I/O components <NUM> may be or include any suitable mechanism, interface, or device to receive external input and to provide output. In some implementations, the I/O components <NUM> may include an interface to receive requests or commands from a user or to provide feedback to the user. In some other implementations, the I/O components <NUM> may include an interface to receive feedback regarding operation of a device (such as a speed and other measurements of a vehicle). For example, the I/O components <NUM> may include (but are not limited to) a graphical user interface, keyboard, mouse, microphone and speakers, squeezable bezel or border of a handheld device, physical buttons, an interface coupled to a communication network of an automobile, a UAV controller, and so on.

The controller <NUM> may include a signal processor <NUM>, which may be one or more processors to process measurements provided by the receiver <NUM> or control operation of the transmitter <NUM> and the receiver <NUM>. In some aspects, the signal processor <NUM> may execute instructions from a memory (such as instructions <NUM> from the memory <NUM> or instructions stored in a separate memory coupled to the signal processor <NUM>). In other aspects, the signal processor <NUM> may include specific hardware for operation. The signal processor <NUM> may alternatively or additionally include a combination of specific hardware and the ability to execute software instructions.

As noted, an image sensor of an active depth sensing system may include one or more photodetectors. Each photodetector may include a photosensitive surface that includes germanium to improve absorption of photons at higher wavelengths (such as greater than <NUM> nanometer wavelength) than a pure silicon photosensitive surface. Operation of a photodetector including germanium may be similar to operation of a photodetector not including germanium. For example, a p-i-n photodiode with an intrinsic layer doped with germanium may operate in a similar manner than a p-i-n photodiode with an intrinsic layer not doped with germanium, except that the p-i-n photodiode with the germanium doped intrinsic layer may have a higher absorption efficiency of photons of specific wavelength light (such as a wavelength greater than <NUM> nanometers). A p-i-n photodiode with an intrinsic layer of germanium crystals may have a higher absorption efficiency, than a photodiode including silicon in the intrinsic layer, of photons of wavelength light greater than <NUM> nanometers.

<FIG> is a flow chart depicting an example operation <NUM> of an image sensor. The example image sensor includes a pixel including a photodetector with a photosensitive surface including germanium. At <NUM>, the photosensitive surface of the photodetector receives light. In some implementations, the light includes a reflection of emitted light for an active depth sensing system. For example, the light may include one or more reflections of a frequency modulated light having a first wavelength that is emitted for indirect TOF depth sensing. In some implementations, the photodetector may include a photodiode, and the photodiode may receive light at an intrinsic layer.

In some implementations, the intrinsic layer may be a silicon layer doped with germanium. In some other implementations, the intrinsic layer may be a germanium crystal layer. The intrinsic layer may be between a p- layer and an n- layer not doped with germanium or otherwise including germanium.

The photosensitive surface of the photodetector may absorb photons of the light (<NUM>). In some implementations, the germanium doped intrinsic layer may absorb photons of the received light (<NUM>). At <NUM>, the photodetector may generate a current based on the absorbed photons. For example, a photodiode may generate the current (such as described above with reference to <FIG>). As noted, the current may vary depending on the intensity of the light received. If the light includes a reflection of the frequency modulated emitted light, the intensity of the light received varies based on the phase of the reflected light as received by the pixel.

In some implementations, an image sensor may enable one or more sampling circuits coupled to the photodiode (<NUM>). Enablement may be based on a phase of the emitted light (such as from an indirect TOF transmitter). For example, referring back to <FIG>, the transistors <NUM> and <NUM> may be activated based on a phased of the emitted signal <NUM> or the inverse emitted signal <NUM> (which may be a phase offset of the emitted signal <NUM>). The one or more enabled sampling circuits may then generate a voltage indicating a phase difference between one or more reflections of the emitted light (as received in the received light) and the emitted light from the indirect TOF transmitter (<NUM>). For example, if the current from the photodiode is below a threshold, an enabled sampling circuit may generate a low voltage signal. If the current from the photodiode is above the threshold, the enabled sampling circuit may generate a high voltage signal. Whether the current is above or below the threshold may correspond to the phase of the reflection of the emitted signal as received by the pixel. In this manner, the voltages may indicate a phase difference between the reflection of the emitted light and the emitted light.

In some implementations, an apparatus may determine a phase difference between the emitted light and a reflection of the emitted light as received at the pixel (such as at the intrinsic layer of the photodiode) (<NUM>). Determining the phase difference is based on the voltages generated by the one or more sampling circuits. For example, for a four-phase demodulation pixel, the voltages generated by the four sampling circuits may be compared (such as which voltages are a low voltage and which voltages are a high voltage). A phase difference may then be determined based on the comparison.

As noted, an apparatus may determine a depth of a surface of an object from the pixel based on the phase difference. In some implementations, the depth may be used to control operation of a device. For example, the indirect TOF system may be a LIDAR system, and the LIDAR system may be used in controlling navigation of a vehicle (such as an automobile or a UAV). In some other implementations, depths may be determined to generate a depth map, provide depths to users, or other suitable applications for active depth sensing systems.

In the description, numerous specific details have been set forth, such as examples of specific components, circuits, and processes to provide a thorough understanding of the present disclosure. The term "coupled" as used herein means connected directly to or connected through one or more intervening components or circuits. Also, in the description and for purposes of explanation, specific nomenclature is set forth to provide a thorough understanding of the present disclosure. However, it will be apparent to one skilled in the art that these specific details may not be required to practice the teachings disclosed herein. In other instances, well-known circuits, systems, and devices are shown in block diagram form to avoid obscuring teachings of the present disclosure. Some portions of the detailed descriptions are presented in terms of procedures, logic blocks, processing and other symbolic representations of operations on data bits within a computer memory. In the present disclosure, a procedure, logic block, process, or the like, is conceived to be a self-consistent sequence of steps or instructions leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, although not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated in a computer system.

Unless specifically stated otherwise, it is appreciated that throughout the present application, discussions utilizing the terms such as "accessing," "receiving," "sending," "using," "selecting," "determining," "normalizing," "multiplying," "averaging," "monitoring," "comparing," "applying," "updating," "measuring," "deriving," "settling" or the like, refer to the actions and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.

In the figures, a single block may be described as performing a function or functions; however, in actual practice, the function or functions performed by that block may be performed in a single component or across multiple components, and/or may be performed using hardware, using software, or using a combination of hardware and software. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps are described below generally in terms of their functionality. Also, the example systems and devices may include components other than those shown, including well-known components such as a processor, memory and the like.

Aspects of the present disclosure are applicable to active depth sensing (such as TOF ranging), and may be included in or coupled to any suitable electronic device or system (such as security systems, smartphones, tablets, laptop computers, digital cameras, vehicles, drones, virtual reality devices, or other devices that may utilize depth sensing). While described with respect to a device having or coupled to one TOF system, aspects of the present disclosure are applicable to devices having any number or type of suitable active depth sensing systems.

The term "device" is not limited to one or a specific number of physical objects (such as one smartphone, one controller, one processing system and so on). As used herein, a device may be any electronic device with one or more parts that may implement at least some portion of this disclosure. While the description and examples use the term "device" to describe various aspects of this disclosure, the term "device" is not limited to a specific configuration, type, or number of objects. Additionally, the term "system" is not limited to multiple components or specific embodiments. For example, a system may be implemented on one or more printed circuit boards or other substrates, have one or more housings, be one or more objects integrated into another device, and may have movable or static components. While the description and examples use the term "system" to describe various aspects of this disclosure, the term "system" is not limited to a specific configuration, type, or number of objects.

The techniques described herein may be implemented in hardware, software, firmware, or any combination thereof, unless specifically described as being implemented in a specific manner. Any features described as modules or components may also be implemented together in an integrated logic device or separately as discrete but interoperable logic devices. If implemented in software (such as a device altering the spatial pattern for an included structured light system), the techniques may be realized at least in part by a non-transitory processor-readable storage medium (such as the memory <NUM> in the example device <NUM> of <FIG>) comprising instructions <NUM> that, when executed by the processor <NUM> (or the controller <NUM> or the signal processor <NUM>), cause the device <NUM> or the depth finding system to perform one or more of the methods described. The non-transitory processor-readable data storage medium (computer readable medium) may form part of a computer program product, which may include packaging materials.

The non-transitory processor-readable storage medium may comprise random access memory (RAM) such as synchronous dynamic random access memory (SDRAM), read only memory (ROM), non-volatile random access memory (NVRAM), electrically erasable programmable read-only memory (EEPROM), FLASH memory, other known storage media, and the like. The techniques additionally, or alternatively, may be realized at least in part by a processor-readable communication medium that carries or communicates code in the form of instructions or data structures and that can be accessed, read, and/or executed by a computer or other processor.

Some of the various illustrative logical blocks, modules, circuits and instructions described in connection with the embodiments disclosed herein may be executed by one or more processors, such as the processor <NUM> or the signal processor <NUM> in the example device <NUM> of <FIG>. Such processor(s) may include but are not limited to one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), application specific instruction set processors (ASIPs), field programmable gate arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. The term "processor," as used herein may refer to any of the foregoing structures or any other structure suitable for implementation of the techniques described herein. In addition, in some aspects, the functionality described herein may be provided within dedicated software modules or hardware modules configured as described herein.

Claim 1:
An apparatus (<NUM>; <NUM>), comprising:
an image sensor including one or more pixels, wherein each pixel of the one or
more pixels includes a photodetector, wherein the photodetector includes a photodiode (<NUM>; <NUM>; <NUM>; <NUM>) including:
a p- layer (<NUM>; <NUM>; <NUM>; <NUM>) of silicon not including germanium;
an n- layer (<NUM>; <NUM>; <NUM>; <NUM>) of silicon not including germanium; and
a photosensitive intrinsic (<NUM>; <NUM>; <NUM>; <NUM>) layer positioned between the player and the n- layer, wherein the photosensitive intrinsic layer includes at least one of the group consisting of :
silicon doped with germanium; and
germanium crystals without silicon to absorb light at least with wavelengths greater than <NUM> nanometers and is configured to generate a current;
an n- well in a p- epitaxial layer (<NUM>), the n-well coupled to the photosensitive intrinsic layer or to the n- layer, wherein the n- well is configured to receive the current; and
a transmit field effect transistor (<NUM>) configured to output the current from the n-well.