Non-contact ultra-low power infrared proximity sensing technology

Infrared proximity sensing is a non-contact gesture proximity roller technology that allows users to quickly sense the user's approach without actual touch. The technology is also increasingly used in a variety of consumer electronic devices, such as mobile phones , computers and other home electronic products. However, most of the proximity sensors on the market currently have a short detection distance of 1~10cm, and infrared LEDs mainly emit infrared rays in a long-term multi-pulse mode, resulting in considerable power consumption and a large amount of waste.

For infrared proximity sensing, Silicon Laboratories (Silicon Labs) of the United States has launched a high-sensitivity infrared proximity sensor Si1143 based on the original Si1120. It not only performs well in long-distance detection and low power consumption, but also adds an SMBus communication interface with three LED drivers, making it more flexible in application.

1. Silicon Labs' infrared proximity sensor series

The Si1143 infrared proximity sensor consists of three infrared LED drivers , infrared photodiodes , an ambient light sensor and a control logic IC . The external transmitting LED can be flexibly installed and configured according to the needs of the user. As shown in Figure 1.

Figure 1

How it works

Si1143 comes with three infrared LED drivers. The main control MCU can control their functions through the I2C interface. When the infrared light emitted by the LED is reflected by the approaching object and received by the built-in infrared photodiode , the light intensity signal is converted into a digital signal through analog-to-digital conversion. The calculated value can be compared with the set threshold value. If the set threshold value is exceeded, an interrupt signal is output from the INT port to the main MCU, and specific operation functions are implemented through corresponding software. For example, a mobile phone application may allow users to zoom in and out on the map or drag the map when changing the distance between the finger and the phone.

Figure 2 Internal block diagram of Si1143

Figure 3 Application schematic diagram of Si1143

2. Advantages of Si1143 Infrared Proximity Sensor

In the field of consumer products, like the Si1120, the Si1143 infrared proximity sensor has two features that people are very concerned about:

1. Low power consumption

Unlike competing infrared LEDs that must be pulsed multiple times over long periods of time to achieve accurate measurements, the Si1143 infrared proximity sensor family uses a patented single-pulse proximity measurement technique (shown in Figure 4) that achieves a 5000- fold improvement in power efficiency , extending battery life.

In addition, when the object approaches a very small distance or is outside the detection range (not working), it can automatically enter low-power mode. The typical power consumption in low-power mode is only 20nA, which is a key feature for portable applications.

Figure 4 Comparison of LED operation methods of Silicon Labs and competitors

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2. High sensitivity

All LEDs have a specific viewing angle. A narrow viewing angle LED means that the energy emitted is more concentrated and can be irradiated farther than a wide viewing angle LED. This means that using a narrow viewing angle IR LED will form a longer detection range in a narrow detection area, as shown in Figure 5. In addition, the LED current of the Si1143 can be set to any value between 6.5mA and 416mA through software. When used in close-range applications, appropriately reducing the LED emission power can save power consumption. At the same time, increasing the LED light power can more stably detect objects at a longer distance, which is more flexible and reasonable in application and energy utilization.

Figure 5 The difference between narrow viewing angle and wide viewing angle IR LED

The Si1143 infrared proximity sensor can detect proximity ranges up to 50cm. If a suitable narrow-angle lens and an infrared filter are used together, the emission half angle of the infrared LED can be small enough to fully converge the emission beam. At the same time, when the infrared LED emission power is large enough, the maximum proximity range can reach 1m. This application is not only limited to handheld electronic products such as mobile phones, but can also be widely used in some security detection equipment or large-screen instruments and equipment.

Unlike Si1120, Si1143 has three LED drivers. When connecting multiple infrared LEDs, if there is only a single LED driver (as shown in Figure 6), the MCU needs to control the MOS tube to drive the LED in time. However, Si1143 (as shown in Figure 7) already has three LED drivers, so it can be directly connected to different LED pins without adding any peripheral devices, which saves cost for hardware design. In addition, Si1143 uses an SMBus interface, which is compatible with I2C communication, has stronger versatility, and is also convenient for software design.

Figure 6

Figure 7

The performance comparison between the Si1140 series infrared proximity sensor and its competitors (as shown in Figure 8):

Figure 8

In summary, the Si1143 infrared proximity sensor series products launched by Silicon Labs can be widely used in various consumer electronic products, such as mobile phones, copiers, scanners, and hygiene products, etc.; at the same time, they can also be widely used in industrial fields such as touch-free panels, machine safety devices, security systems, and ATMs.

Shiqiang Telecom is an authorized agent of Silicon Labs in Greater China and can provide corresponding DEMO boards as well as complete and feasible software, information and technical support for this series of products and related applications.