High voltage amplifier

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Application notes

Application notes
Be sure to read our new application notes about driving MEMS and piezo actuators

Application notes

High voltage amplifiers - How fast are they really?

High voltage amplifier performance in terms of speed is not only determined by the bandwidth and the slew rate, but also by the maximum sustainable current and the capacitance of the load. In this application note we discuss the specifications of high voltage amplifiers required to determine whether they are suitable for a certain amplifier-load combination. The corresponding output current calculator can be used to estimate the current and slew rate required to drive a certain capacitive load.

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High voltage amplifiers - So you think you have noise!

The lowest attainable noise voltage level using a high voltage amplifier is influenced by such factors as the amplifiers' intrinsic (white) noise level, its gain, its capacitively loaded bandwidth, and external interference. In this application note we focus on different aspects of noise, and, in the second half of the application note, interference. Interference is often coupled into the measurement system by electric fields, magnetic fields, and conducted currents. We discuss common pitfalls in amplifier noise assessment, and practical examples and recommendations.

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High voltage amplifiers and the ubiquitous 50 Ohm: caveats and benefits

Every experimental scientist working with electronic measurement equipment will one day or another find him/herself puzzled by an inexplicable factor two in gain. The reason is that almost all electronic equipment for high frequency use (say 1MHz and beyond) is equipped with 50 Ohm in- and/or output resistors. In this application note we discuss correct 50 Ohm interfacing. This prevents reflections and signal distortion caused by the finite speed of light, and the corresponding finite time it takes for an electronic signal to traverse a length of cable.

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Driving piezoelectric actuators with high voltage amplifiers, PART I - Piezo materials, applications, precision, speed, and damping of resonances

In this application note, many piezo-related topics are introduced and discussed briefly. We cover the basic piezoelectric effect, the hysteresis of piezo's, and how different types of piezo actuators are constructed. Application examples are presented, such as scanning probe microscope scanners, stick-slip motors, and piezoelectric transformers. Because piezo's are often used in precision positioning systems, decoupling and damping of external vibrations are also covered. Piezo positioners can have exceptionally high positioning resolution and repeatability. Hysteresis can be reduced by negative feedback using a position sensor signal, and by charge control. Finally, recommendations are given for choosing an optimal network to connect the piezo to the amplifier, in order to damp the resonances of a piezo actuator.

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Driving piezoelectric actuators with high voltage amplifiers, PART II - The theory and practice of optimal electronic damping

The high stiffness and low mass of a piezo actuator make it very fast. But because it has a low internal mechanical damping this also results in the tendency of piezo's to severely resonate, which compromises high-speed operation. It is best not to connect a piezo directly to the piezo driver, but via a suitable coupling network that minimizes the ringing of the piezo. In most cases this coupling network can consist of a single low-valued resistor. The inclusion of this resistor can change the resonance amplitude and time it takes for the resonance to 'die out' by a factor ten or more. This application note is based on research carried out at Falco Systems regarding the exact nature of electronic piezo resonance damping. It serves as a practical introduction to the topic and offers enough information to understand why a damping resistor is necessary and to choose and use an optimum valued resistor.

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The electrostatic actuation of MEMS with high voltage amplifiers - From comb drive levitation and pull-in to dielectric charging and position noise

In this application note, a comprehensive overview is given of the issues to be reckoned with when driving high-performance electrostatic MEMS (micro-electromechanical systems) actuators with high voltage amplifiers. We discuss the manufacturing of MEMS devices, their handling, and reliability. MEMS actuation principles are introduced, and electrostatic comb drive and parallel plate actuators are explored in detail. We deal with the influence of dielectric charging, and how to prevent it. Finally, we discuss how high voltage amplifier noise and thermal noise, and linearity, influence positioning resolution and accuracy.

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Quick and dirty MEMS design

This equations summary form belongs to the Falco Systems application note 'The electrostatic actuation of MEMS with high voltage amplifiers: from comb drive levitation and pull-in to dielectric charging and position noise'. It lists the information required to do a fast reality check for MEMS designs, a 'quick and dirty' method to do a complete design or design assessment, and as a complement to FEM (finite element modeling). If the geometrical values are entered in the Excel sheet, it allows one to calculate actuation voltages, the corresponding forces, and the displacements.

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