原标题：Silabs Si114x低功耗红外接近传感器解决方案

　　Silabs 公司的Si1141/42/43是低功耗红外接近和环境光传感器,集成了I2C数字接口和可编程事件中断输出. Si1141/42/43无接触传感器包括一个ADC,高灵敏度可见光和红外光电二极管, 数字信号处理器,以及15种可选择驱动水平的一/二/三个红外光LED驱动器,每个LED驱动器的电流从5.6mA到360mA,接近检测距离从1cm到大于1米,LED驱动器的脉宽为25.6 μs,工作电压1.8 - 3.6 V,待机电流小于500nA,可用在手持机如电子书阅读器,笔记本电脑/上网本,音频产品,烟雾检测器,无接触开关和滑动,消费类电子,工业自动化以及显示器背光控制等.本文介绍了Si1141/42/43主要特性, 功能方框图, 单电源和双电源应用电路, 烟雾检测方框图以及开发套件Si1140DK电路图.

　　The Si1141/42/43 is a low-power, reflectance-based, infrared proximity and ambient light sensor with I2C digital interface and programmable-event interrupt output. This touchless sensor IC includes an analog-to-digital converter, integrated highsensitivity visible and infrared photodiodes, digital signal processor, and one, two, or three integrated infrared LED drivers with fifteen selectable drive levels. The Si1141/ 42/43 offers excellent performance under a wide dynamic range and a variety of light sources including direct sunlight. The Si1141/42/43 can also work under dark glass covers. The photodiode response and associated digital conversion circuitry provide excellent immunity to artificial light flicker noise and natural light flutter noise. With two or more LEDs, the Si1142/43 is capable of supporting multiple-axis proximity motion detection. The Si1141/42/43 devices are provided in a 10-lead 2x2 mm QFN package and are capable of operation from 1.8 to 3.6 V over the –40 to +85℃ temperature range.

　　Si1141/42/43主要特性:

　　QuickSense™ integrated infrared proximity detector

　　Proximity detection adjustable from under 1 cm to over 1 m

　　Three independent LED drivers

　　15 current settings from 5.6 mA to 360 mA for each LED driver

　　25.6 μs LED driver pulse width

　　500 mm proximity range with single pulse (<2.5 klx)

　　150 mm proximity range with single pulse (>2.5 klx)

　　Operates at up to 128 klx (direct sunlight)

　　Minimum reflectance sensitivity <1μW/cm2

　　High EMI immunity without shielded packaging

　　QuickSense™ integrated ambient light sensor

　　10 mlx resolution possible, allowing operation under dark glass

　　1 to 128 klx dynamic range possible across two ADC range settings

　　17-bit resolution

　　Accurate lux measurements possible with IR correction algorithm

　　25.6 μs measurement cycle keeps total power consumption duty cycle low without compromising performance or noise immunity

　　Industry’s lowest power consumption

　　1.8 to 3.6 V supply voltage

　　9 μA average current (LED pulsed 25.6 μs every 800 ms at 180 mA plus 3 μA Si114x supply)

　　<500 nA standby current

　　Internal and external wake support

　　Built-in voltage supply monitor and power-on reset controller

　　Serial communications

　　Up to 3.4 Mbps data rate

　　Slave mode hardware address decoding

　　Small-outline 10-lead 2x2 mm QFN

　　Temperature Range

　　–40to +85℃

　　Si1141/42/43应用:

　　Handsets

　　E-book readers

　　Notebooks/Netbooks

　　Portable consumer electronics

　　Audio products

　　Security panels

　　Tamper detection circuits

　　Dispensers

　　Valve controls

　　Smoke detectors

　　Touchless switches

　　Touchless sliders

　　Occupancy sensors

　　Consumer electronics

　　Industrial automation

　　Display backlighting control

　　Photo-interrupters

　　图1.Si114x功能方框图

　　图2.Si1141单电源应用电路

　　图3.Si1143双电源应用电路

　　Both the Si1120 and the Si1141 can be used in smoke detector applications. Although the feasibility study was done using the Si1120, the Si1141 is the recommended device due to its higher measurement sensitivity and lower power. The Si1141 also has the ability to perform measurements autonomously, allowing the C8051F990 to be kept in its sleep state until a significant reflectance has been measured. This lowers overall system power consumption and results in longer battery life.

　　Si1141 is initialized to perform measurement every 1 second in autonomous mode. Therefore, once initialized, an interrupt is received by the C8051F990 on its P0.6 input. Measurement is then read using the I2C bus.

　　Before it is compared to the alarm threshold, this raw data is treated as follows:

　　1. Raw data is first subtracted to the last noise level value. Given the known measurement pace, this value can be compared to its equivalent trend constants.

　　2. If the rate of change is below the minimum trend, it will be flagged as “noise” and exponentially averaged to the previous noise value to get the new noise level.

　　3. If the rate of change is above the maximum trend, it is simply discarded since this is a too fast and, typically, generated by an insect. If this is the first occurrence, it starts a counter to generate a maintenance alarm in case it lasts too long. The counter is reset in all other cases.

　　4. If the rate of change is between the two trend values, the noise level remains untouched and a flag is set to signify that the next measurement should be compared to this value instead of the noise level. This is done until the alarm threshold is trigged or the level falls back to noise.

　　5. Finally, the Si1141 interrupt register is cleared to enable the next wake-up vector.

　　图4.Si1141烟雾检测方框图

　　图5. C8051F990 MCU方框图

　　Si1140开发套件Si1140DK

　　The Si1140DK is intended as an evaluation and development platform for the Si1143 infrared proximity and ambient light sensor. As shown in Figure 1, the main components of the Si1143 Evaluation Board (Si1143_EB) are the Si1143 sensor (U2), the C8051F800 microcontroller (U1), and the infrared emitters (DS1 through DS9). On this PCB, the infrared emitters used are OSRAM part number SFH 4056. These emitters have a power rating of 40 mW and a half-angle of 22 degrees. Other emitters with different characteristics may also be used, depending on the specific application requirements.

　　The example firmware for the kit measures the infrared light energy detected by the Si1143 while each of three infrared emitters are independently activated. The infrared light from these emitters will be reflected back to the Si1143 by any object that is placed in proximity to the sensor. X, Y, and Z positions can be calculated from these measurements. If no object is close enough to the board, the measured signal levels will fall below predetermined thresholds, and the position calculations will not update. The Si1143’s ambient light sensor (ALS) is also monitored by the firmware. The example firmware is intended to be used in conjunction with the QuickSenseTM Performance Analysis Tool to provide user feedback. In addition to calculating the current position, the firmware is able to detect different gestures from the infrared sensor.

　　开发套件Si1140DK包括:

　　The Si1140 Development Kit contains the following items:

　　Si1143 Evaluation Board

　　

　　Si1140DK Quick Start Guide

　　

　　1 USB Cable

　　图6.开发套件Si1140DK外形图

　　图7.开发套件Si1140DK电路图