Piezofilm Sensor Amplifier for Thermal Signal Extraction

The design of a reliable and efficient amplifier is crucial when working with high-gain circuits, particularly those that involve piezofilm sensors. One such application is the extraction of thermal signals from these sensors, which can be used to detect temperature changes. In this article, we will explore the concept of piezofilm sensors, their characteristics, and a circuit design that utilizes a differential charge amplifier to extract the thermal signal.

Piezofilm sensors are designed to convert thermal energy into electrical energy, making them suitable for applications such as temperature measurement. They work by converting mechanical stress caused by thermal expansion or contraction into an electrical signal. This conversion process is known as piezoelectricity, where certain materials generate an electric charge when subjected to mechanical stress.

The circuit design presented here consists of a differential charge amplifier followed by a differential-to-single-ended amplifier. The sensor has high output impedance and requires a high-impedance buffer amplifier to drive the subsequent stages. The electrical analog of a piezofilm sensor is a capacitor in series with a voltage source, which makes it essential to use an op amp with low supply current.

The circuit design uses three op amps (IC1) in a classical instrumentation amplifier configuration. This configuration provides high input impedance and excellent common-mode rejection ratio, making it suitable for applications where the input signal is weak and prone to noise interference. The differential stage rejects resistor-generated thermal noise and acts as a first-order high-pass filter, effectively removing low-frequency noise from the signal.

The design also includes alternative configurations that can be used to overcome typical circuit limitations. These include using different component values or modifying the amplifier configuration to achieve better performance in specific applications.

In summary, the article provides an overview of piezofilm sensors and their characteristics, as well as a circuit design that utilizes a differential charge amplifier to extract the thermal signal from these sensors. The design is suitable for applications where high-impedance buffer amplifiers are required, such as temperature measurement systems.