6/18/2023 0 Comments Piezo crystal op ampTaking integration further, another alternative is to use devices that employ MEMS technology to put a piezo sensor and its associated circuitry in a single package. This is important because high-impedance circuits can be very sensitive to subtle design and layout issues. (Source: Texas Instruments)Īlthough the circuit using this op amp still requires a handful of support components, the overall circuit design is simpler and has a much less critical physical placement than one based on the JFET alone. This CMOS-input op amp features 360-mV input offset voltage, 17 nV/√Hz input noise voltage, and 2-pA input bias current-specifications that are a good match when using a piezo transducer for high-accuracy, high-resolution measurements in medical, scientific, and industrial applications.įigure 2: The TLV2775 CMOS-input op amp from Texas Instruments is well-suited for use in signal-conditioning front-end circuits for high-impedance sources such as piezo transducers. The JFET must be properly biased, and often needs added temperature-compensation to ensure accuracy and stability if the ambient environment is not controlled or stable.įor this reason, many designers instead prefer to use a high-impedance op amp such as the TLV2771 series from Texas Instruments (Figure 2). While using a JFET is a viable solution, it is only a partial answer to the overall interface-circuit requirement. This discrete device typically has an input impedance at least 1 GΩ (109 Ω) along with bandwidth into the high kHz and even higher, which is needed for high-frequency vibration measurements. One way to satisfy these interface requirements is to connect the piezo sensor to a junction field-effect transistor (JFET). This impedance matching is a consequence of the power-transfer law, where the impedance of a source and its load must be complex conjugates to achieve maximum power transfer. Due to its inherently high electrical impedance, it can only deliver a sufficiently strong signal to the electronic circuitry if the interfacing signal-conditioning circuit also has very high impedance. Using Piezo Devices as Strain SensorsĪs a basic transducer, the piezo-based unit is very simple and rugged, but it has a unique electrical aspect. Depending on material, these sensors can withstand and work at accelerations of several thousand g. For this reason, they are often used as transducers for sensing pressure-related physical parameters, which includes pressure itself, as well as its related manifestations: acceleration, impact, altitude (air pressure), and vibration. Since they have a crystalline structure, many piezoelectric materials are quite hard and can withstand a great deal of stress without changing their basic characteristics or failing. This spark ignites the gas and initiates a flame (but the current level is so low that there is no danger of shock). (Source: Seiko Epson Corp.)Įven a gas-fired grill can have a piezoelectric element, using a built-in crystal that generates a spark of several hundred volts when the user turns a knob and so squeezes the crystal. Piezo materials are also used as actuators that can be directed to move in precise nanometer-size steps, such as for micromotors in applications ranging from high-end scientific instruments down to autofocusing in mass-market consumer cameras.įigure 1: The piezoelectric effect has a dual nature: a) applying stress on a crystal causes it to generate a voltage while b) applying a voltage to the crystal causes it to deform, both in predictable and repeatable relationships. These two principles have been adapted to many applications the best-known one is use of quartz as a resonant element in an oscillator circuit.
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