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MEMS Mirror Steering
What is MEMS?
MEMS (Micro-Electro-Mechanical Systems) is a technology which allows the fabrication of miniature mechanical and electro-mechanical devices using silicon fabrication techniques. Since they are fabricated with the same techniques used to create semiconductor ICs, it is possible to manufacture different MEMS structures in a reliable and cost-effective manner. MEMS systems have found multiple applications in many varied fields like sensors, RF timing, Microfluidics and mirrors for optical signal processing.
What is MEMS Mirror Steering?Mirrors are one of the growing applications for MEMS technology given the proliferation of the use of lasers for multiple applications. MEMS mirror steering uses a MEMS based mirror to deflect a laser beam in both static and dynamic operations. Static operation requires the mirror to deflect to a known angle accurately and maintain the angle almost indefinitely without significant drift. Dynamic operation requires the mirror to be able to track a programmed path accurately with fast response and high resolution
What Are the Trends in MEMS Mirror Steering?
MEMS mirror steering has found multiple applications in recent times.
- Optical networks – MEMS mirrors are used in fiber-to-fiber optical switching
- Projection displays – Head-up displays and laser projectors (pico projectors)
- Automotive safety and autonomous vehicles - LIDAR (Light Detection And Ranging), Laser headlamps
- AR/VR – Tracking and position measurement
- 3D printing
What Does a Typical MEMS Mirror System Look Like?
MEMS mirrors typically need a high voltage driver IC to control the position of the mirror. A typical MEMS mirror, for example, would need drive voltages in the range of 200V – 300V. The high-voltage mirror driver would get its input from a microcontroller or FPGA in the system which is responsible to determining the drive voltages that need to be applied. The same microcontroller also controls the laser diode driver to synchronize the operation of the laser diode and the mirror. A high-resolution Digital to Analog Converter (DAC) is used to interface the digital output of the controller to the analog input of the amplifier. The requirements of the DAC will depend on the resolution and speed requirements of the system. A photo-diode can be used for feedback in case of closed loop systems.
MEMS Mirror Steering Application Challenges
There are multiple blocks that are needed to implement a MEMS mirror steering system successfully.
- The main controller must be capable of processing data at high speeds to enable fast computation based on the feedback signals. It also needs to have Analog to Digital Converters (ADCs) with high sampling rates to collect the feedback signal with sufficient resolution. Sufficiently large memory will allow for larger number of samples which can be stored and processed.
- The DAC should also have sufficient speed and resolution to enable the control of mirror with high speed and precision.
- The high voltage driver needs to amplify a low voltage DAC output to the high voltages required to operate the mirror. Typical voltages needed to operate MEMS mirror are in the range of 200-300V. The amplifiers should also have high bandwidth and slew rates (for fast steering in dynamic operation) as well as a low drift (to maintain mirror position for static operations).
- The high voltage power supply has to generate 200-300V DC voltages from a very low input voltage (eg: 3.3V for a Li-ion battery based pico projector). Since these applications are usually space constrained, the overall solution has to have a small form factor.
- The Laser Driver needs to change the intensity of the laser at the pixel rate, to project high resolution images. This can be quite fast for applications like HDMI video. The driver takes parallel digital data from the external interface and converts this into a controlled analog current for the laser, synchronized with the horizontal and vertical scanning of the MEMS.
MEMS Laser Demo Available:
Introducing the Laser Demo 001, a development tool created by MEMS mirror supplier Mirrorcle Technologies, Inc. featuring control and drive electronics from Microchip Technology, Inc.
The development tool provides a means of evaluating laser beam steering technology, while enabling solutions development for many different consumer, industrial, automotive, and other applications.
The HV265 is a four-channel high-voltage operational amplifier gate array with an optional internal feedback resistor network.
- Four independent high-voltage amplifiers
- 205V output swing
- .02V/µs minimum output slew rate for CLOAD to 200 pF (and ZOUT < 1 kOhm)
- Fixed gain of 82V/V, 30 kHz gain-bandwidth product
- High-value internal feedback SiCr resistors to set gain (if internal gain set used)
- Less than 10 ms settling time
HV264 is a quad high-voltage amplifier array integrated circuit. It operates on a 200V high-voltage supply and a 5.0V low-voltage supply. Each channel has its own input and output.
- Four independent high-voltage amplifiers
- 190V output swing
- 9.0V/µs typical output slew rate
- Fixed gain of 66.7V/V
The HV9150 is a high-output voltage hysteretic mode step up DC/DC controller that has both a built-in charge pump converter and a linear regulator for a wide range of input voltage. The charge pump converter mode is ideal for battery powered applications.
- Low-input voltage: 2.7V
- Wide output voltage range: 6V to 500V
- 5W maximum output power with external MOSFET driver
- Built-in charge pump converter for the gate driver