|Laser Diode Driver||请参考：激光驱动器|
|LCC||1. 无引线陶瓷芯片承载封装或无引线芯片承载封装：一种IC封装形式，采用陶瓷材料，没有引线(引脚)。与印刷电路板的连接不是采用传统的芯片边沿的金属焊盘。例如：Maxim的20引脚LCC封装图 (PDF, English only)。
2. 引线芯片承载封装，也称为PLCC或塑料引线芯片承载封装：是一种方形表面贴装芯片封装形式，芯片四周带有引线(引脚)。例如：Maxim的20引脚PLCC封装图 (PDF, English only)。
|LDO Regulator Low Dropout Regulator||请参考：LDO|
|Leaded Chip Carrier||请参考：LCC|
|Leadless Chip Carrier||请参考：LCC|
应用笔记：Driving LEDs in Battery-Operated Applications: Controlling Brightness Power Efficiently详细介绍了LED工作原理，并讨论了电流与LED亮度的关系以及不同类型的多LED驱动方案对LED亮度匹配的影响。
LiDAR (light detection and ranging) is a remote sensing method that uses laser beams to create a 3D scan of the surrounding area. LiDAR is an important means of proximity sensing in autonomous vehicles.
What is LiDAR and how does it work?
LiDAR works by emitting pulses of laser light and measuring the return time between the emitted signal and the signal that is reflected after bouncing off of a nearby object. Since LiDAR uses light signals, the distance to the object is easily calculated by multiplying the time of flight by the speed of light. The use of light also makes for very quick return times.
The distance map in (B) shows the objects detected in (A) by a LiDAR laser/receiver system. The closest object (in red) has the shortest time of flight, while the farthest (in green) has the longest.
By continually emitting these short laser bursts, and in multiple directions, the system can create a distance map of all of the surrounding objects that updates instantly and continuously.
Illustration of autonomous vehicles emitting LiDAR signals in multiple directions to detect objects on the road.
How does a LiDAR laser/receiver system work?
The block diagram above shows a typical operating circuit. The laser driver initiates the light pulse towards the object, and the returned signal reflects into the photodiode D1 which converts the light to current. The transimpedance amplifier TIA1 converts the current to voltage and amplifies the signal to then be sent to the comparator COMP1, which converts the analog signal to a digital one. The D2/TIA2/COMP2 system works similarly to record the initial signal, and all of this information is processed and stored by the MCU.
LiDAR vs. radar
LiDAR and radar are similar in that they both measure time of flight to determine distance from an object, and the difference is what type of signal they use. Where LiDAR is Light Detection and Ranging, radar is Radio Detection and Ranging, and these are the types of waves that each system emits. Light waves are in the nm to μm wavelength range, where radio waves are in the cm to km wavelength range.
LiDAR’s smaller wavelengths make it able to create more precise and accurate distance maps, detecting smaller objects and greater detail. Radar’s longer wavelength range makes it less sensitive to changes in the medium through which it travels (such as poor weather). Because of these differences, the two are often used together (sometimes with cameras) to form vision and driving capabilities that exceed those of humans.
Light sensors are a type of photodetector (also called photosensors) that detect light. Different types of light sensors can be used to measure illuminance, respond to changes in the amount of light received, or convert light to electricity.
What are the different types of light sensors?
Common types of light sensors are photodiodes, photoresistors, phototransistors, and photovoltaic light sensors. These components can be used in applications such as light sensing in mobile devices, automatic outdoor lighting, proximity sensors, and renewable energy.
Photodiodes convert light into an electrical current. They are p-n junction devices that are similar to normal diodes. A p-n junction device consists of a p-type and an n-type semiconducting material. The “p” stands for “positive” due to the material’s excess of electron holes, and the “n” stands for “negative” due to an excess of electrons. This means that current can only flow in one direction through the boundary. In a photodiode, these electron hole pairs are formed when the energy from the incident light is absorbed by the device.
Photoresistors (also known as light-dependent resistors or LDRs) are passive devices that decrease resistance in proportion to the amount of light received. Light forming electron hole pairs increases conductivity and therefore decreases resistivity.
Phototransistors switch or amplify signals similarly to regular transistors, with the current applied to the terminals being created from exposure to light.
Photovoltaic (or solar cells) convert light into electricity by generating voltage and electric current by way of the photovoltaic effect exhibited by its semiconducting components.
How do light sensors work?
Light sensors work by the photoelectric effect. Light can behave as a particle, referred to as a photon. When a photon hits the metal surface of the light sensor, the energy of the light is absorbed by the electrons, increasing their kinetic energy and allowing them to be emitted from the material. This movement of electrons, and therefore charge, is electrical current.
The photovoltaic effect is similar to the photoelectric effect in that the light is absorbed by electrons, causing them to be in a higher-energy state. In the photoelectric effect, the electrons are ejected from the material completely. In the photovoltaic effect, the electrons are excited from the valence band into the conduction band, but remain within the same material.
VOUT = k*VIN
|Linear Fan Control||请参考：风扇控制器 - 线性|
|Linear Feedback Shift Register||请参考：LFSR|
请参考应用笔记660："Regulator topologies for battery-powered systems"。
Maxim NV SRAM和时钟产品大多采用扣式、BR (氟化碳)原锂电池(不可充电电池)；在微控制器和数据保持产品中采用扣式、CR (二氧化锰)原电池；在一些新产品中使用了“锂锰” (ML)电池, 其化学特性非常接近CR, 但它是二次扣式锂电池(可充电)。
|Lithium-ion batteries||锂和锂离子: 化学成份基于锂元素(一种具有高活动性的金属元素)的电池。锂电池常常用来为便携式产品供电，如：蜂窝电话、膝上电脑、MP3播放器等，通常用于功耗低、使用寿命长的产品，例如，为存储器、时钟供电。
锂电池有一种典型的扣式封装，常常用于为Maxim的非易失静态RAM (NV SRAM)和时钟电路(如实时时钟)等产品供电。
|Local Interconnect Network||请参考：LIN|
|Local Multipoint Distribution Service||请参考：LMDS|
|Local Temperature Sensor||集成电路内部用于检测本身管芯温度的单元或功能电路。|
|Long Term Evolution||LTE (长期演进)是由第三代合作伙伴计划(3GPP)开发的高速移动通信无线标准。LTE是GSM/UMTS标准的演进。|
|Low Batt. Det.||低电池电量检测器。|
|Low Drop Out||请参考：LDO|
|Low Dropout Linear Regulator||请参考：LDO|
|Low Frequency Gain Boost||请参考：低音增强|
|Low Line O/P||低电压输出。|
|Low Noise Amplifier||请参考：LNA|
|Low Voltage Differential Signaling||请参考：LVDS|
|Low Voltage Emitter Coupled Logic||请参考：LVECL|
|Low Voltage Positive Emitter Coupled Logic||请参考：LVPECL|
|Low Voltage Transistor-Transistor Logic||请参考：LVTTL|
A low-pass filter (LPF) is a circuit that only passes signals below its cutoff frequency while attenuating all signals above it. It is the complement of a high-pass filter, which only passes signals above its cutoff frequency and attenuates all signals below it.
What is a low-pass filter used for?
Low-pass filters have applications such as anti-aliasing, reconstruction, and speech processing, and can be used in audio amplifiers, equalizers, and speakers.
Low-pass filters can also be used in conjunction with high-pass filters to form bandpass, band-stop, and notch filters. A bandpass filter passes a range of frequencies while attenuating all frequencies outside of the band. A band-stop filter (also called a band reject filter) does the opposite, attenuating signals within its stopband while passing all frequencies outside of it. Notch filters are a type of band-stop filter that attenuate a very narrow set of frequencies, which can be created from a combination of low-pass and high-pass filters with cutoff frequencies very close to each other.
What is a low-pass filter circuit?
There are many different low-pass filter circuits, which are characterized by their order and amplitude characteristic or the type of polynomial that describes it (Butterworth, Chebyshev, Elliptic, or Bessel):
Butterworth - response that is flat in the passband and an adequate rate of rolloff.
Chebyshev - frequency cutoff is steeper than that of a Butterworth, at the cost of a variation in amplitude known as ripple in the passband.
Elliptic (or Cauer) - compared to the Chebyshev, the stopband cutoff is sharper (without incurring more passband ripple), but transient response is worse.
Bessel - represents a trade-off in the opposite direction from the Butterworth. Transient response is improved, but at the expense of a less steep cutoff in the stopband.
Amplitude and group delay vs. frequency for various filter types normalized to a 1-rad bandwidth.
For more on first and second order filters, as well as Butterworth, Chebyshev, Elliptic, and Bessel filters, see Tutorial 733: A Filter Primer.
|Luminance||1. 每单位面积发光强度，以cd/m²: (每平方米堪)为单位。一般情况下不能直接换算成“亮度”。
2. 视频信号的黑、白分量，用“Y”分量表示。 Y/C或Y/Pb/Pr视频信号与亮度信号、色度分量组合构成复合信号。