Active shutter 3D glasses solution based on EFM32

The rise of 3D movies, the hot sales of 3D TVs, and the launch of CCTV's 3D experimental channel further stimulated the collective development of the 3D industry chain in 2012. As an important accessory product for watching stereoscopic images, 3D glasses have also become a big cake, triggering a strong market effect.

3D glasses are mainly divided into three types: chromatic aberration, polarized and active. Among them, active shutter 3D glasses have become the market's first choice because of their excellent viewing effect, easy to achieve full HD and a large number of blue-ray 3D film sources.

At present, active shutter 3D glasses mainly use infrared signals to synchronize with the display screen. Common methods of receiving infrared signals are:

1. Integrated infrared receiver

Currently, many manufacturers integrate photodiodes and filter amplifier circuits into integrated receiver heads. This type of receiver head has a very small size and is widely used in the receiving circuit of infrared remote controllers. However, due to the low time resolution of the received signal, it cannot distinguish the details of the infrared signal, which seriously restricts its application in shutter-type 3D glasses.

2. Photodiode plus op amp

By using discrete photodiodes, resistors and capacitors and op amps to build infrared signal filtering and amplification circuits, it is possible to design circuits with appropriate filtering bandwidth and amplification factor for shutter-type 3D TV signals. The disadvantage is that the addition of op amps and resistors and capacitors increases the circuit board area, making the 3D glasses look bulky.

For the above reasons, we hope to have a solution that is both customizable and takes up as little space as possible.

The EFM32 from Energymicro of Norway is a high-performance, low-power 32-bit microcontroller with internally integrated analog op amps and analog comparators. It is a solution that is both customizable and takes up as little space as possible, making a single-chip signal chain solution possible.

Active shutter 3D glasses solution based on EFM32

EFM32 is designed based on the ARM Cortex-M3 core and has outstanding low power consumption characteristics. It is suitable for "three meters" (electricity meter, water/heat meter, gas meter), industrial control, alarm security system, health and sports application system, handheld medical equipment, smart home control and other fields with very stringent requirements on power consumption.

The following is a block diagram of the structure of active shutter 3D glasses, including the main processor, 3D glasses dedicated power supply, charging and boost driver chips, batteries and LCD lenses.

Active shutter 3D glasses structure diagram

Source: Beigaozhi Technology Team

a. Main controller

EFM32 can work in 5 working modes from EM0 to EM4. The flexible and diverse power consumption configuration can greatly reduce the power consumption of the whole device. When the glasses are in standby mode, the EM4 mode of EFM32 can be used. At this time, the GPIO port can still be used to wake up the MCU, and the power consumption is only 900nA. The wake-up time of only 2us and the peripheral reflex system allow the MCU core to be in the sleep state of EM3 most of the time, thereby further reducing power consumption.

b. Power supply, charging and boost driver chip for 3D glasses

Now some manufacturers on the market have launched driver chips that integrate power supply, charging, boost and analog switch, which not only simplifies the circuit design but also greatly reduces the PCB area.

c. LCD lens

The common LCD lenses on the market generally work at ±10V, so generally require a 10V boost circuit and analog switch to drive, here we use a dedicated chip to achieve this.

d.Battery

You can choose button batteries or lithium batteries.

Advantages of the EFM32 solution

Compared with the active shutter 3D glasses implemented by traditional 8-bit and 16-bit microcontrollers, this solution based on EFM32 has the following advantages:

1. Ultra-low power consumption

EFM32 is the world's lowest power 32-bit microcontroller. When processing synchronization signals, the power consumption in EM0 mode is only 150uA/MHz, and then it can enter the low-power mode of EM3, at which time the core power consumption is as low as 0.59uA. Since active shutter 3D glasses are powered by batteries, they have high requirements for power consumption, so the low power consumption of EFM32 has obvious advantages.

2. High integration and high performance

EFM32 is a Cortex-M3 core, and the core's instruction efficiency and code density are higher than those of traditional 8-bit microcontrollers. The built-in integrated analog op amp and analog comparator, as well as the programmable op amp feedback loop, enable a single EFM32 chip to implement a complete signal chain. The overall design can be completed with only two chips, EFM32 + 3D glasses professional chip.

3. Good scalability

EFM32's TG, G, and GG series have good compatibility, and chips of the same model but different series are pin-pin compatible, ensuring that users can tailor different functional requirements on a unified hardware platform. Flash resources range from the lowest 4KB to 1024KB, and RAM resources range from 2KB to 128KB.

Summarize

EFM32 has excellent low power consumption characteristics, and a single chip peripheral can complete the amplification and processing of the entire signal. It is very suitable for active shutter 3D glasses applications that have certain requirements for low power consumption and space. The EFM32 core adopts the currently popular Cortex-M3 design, which greatly shortens the development time of developers. EFM32 has rich peripherals, which provides conditions for system expansion functions and cost reduction.