“Apple’s products are always released quietly. Affected by the epidemic, the originally planned Apple spring conference could not be held, so several new products such as iPad Pro, MacBook Air and Mac mini were quietly put on the official website.
Apple’s products are always released quietly. Affected by the epidemic, the originally planned Apple spring conference could not be held, so several new products such as iPad Pro, MacBook Air and Mac mini were quietly put on the official website.
Among them, the most popular one is the iPad Pro. Its functional modules are the same as most iPad products. What really makes the iPad Pro a black technology is not the Yuba dual camera behind it, but the dToF lidar mounted next to the camera. The iPad Pro has also become Apple’s first product to use ToF technology.
Many people may not understand what ToF is. ToF is the abbreviation of Time of flight, which literally means flight time. The so-called time-of-flight 3D imaging is to continuously send light pulses to the target, and then use the sensor to receive the light returned from the object, and obtain the target distance by detecting the flight (round-trip) time of the light pulse.
The ToF ranging method is a two-way ranging technology. It mainly uses the flight time of the signal to and from the two asynchronous transceivers (Transceiver) (or the reflected surface) to measure the distance between nodes. The traditional ranging technology is divided into two-way ranging technology and one-way ranging technology.
When the signal level is better modulated or in a non-line-of-sight line-of-sight environment, the estimation result based on the RSSI (Received Signal Strength Indication) ranging method is ideal; in a line-of-sight environment, the ToF distance estimation is based on The method can make up for the deficiency of RSSI-based distance estimation method.
ToF is further divided into iToF (indirect time-of-flight) and dToF (direct time-of-flight). The main difference between the two is the emission and reflection of light.
iToF is a method of indirectly measuring time. Most of the indirect measurement schemes use the method of measuring phase offset, that is, the phase difference between the transmitted sine wave and the received sine wave, the flight time t, that is, the distance Z, is a function of the phase difference, so it can be solved for Z, the sine wave mentioned above: the abscissa is the time, and the ordinate is the light intensity. It is precisely because the time resolution of the photodiode based on forward bias and its measurement circuit is relatively low, in order to avoid the interference of various factors, the method of measuring the phase offset is adopted to achieve the effect of being lower than the time resolution of the hardware system.
Whereas dToF is a direct measurement of time of flight. ToF originally hoped to measure time directly to correspond to distance, but the measurement system that can reach ps-level resolution is slower to mature, namely SPAD+TDC. SPAD single photon avalanche diode, a single photon avalanche diode, which is a device that can generate a response current in ps-level time. Its working principle is to use a reverse-biased photodiode to make it work when it exceeds the breakdown voltage. In a very small voltage range that has not yet broken down, the diode is in a very sensitive working range, so as long as there is a weak light signal, it can cause it to generate avalanche current, and the response speed is extremely fast.