Design considerations for micro sensors

The design of the micro weighing sensor is the crystallization of experience and technology. It is generally understood that the sensor converts a physical quantity into a description that can be expressed in another intuitive way through the circuit. For example, it can be converted into higher voltage and current signals that only depend on the measured physical quantity, and then displayed. Therefore, several points should be noted:

1. Generally, the measured physical quantity is very small, and usually has the inherent conversion noise as the physical conversion element of the sensor. For example, when the signal strength of the sensor is 0.1~1uV at a magnification of 1, the background noise signal has such a large level that it is even annihilated. How to get the useful signal as much as possible and reduce the noise is the first problem to be solved in sensor design.

2. The sensor circuit must be simple and refined. It is assumed that the amplification loop with a 3-stage amplification circuit and a 2-stage active filter amplifies the signal as well as the noise. If the noise does not deviate significantly from the useful signal spectrum, no matter how the filtering is performed, the signal to noise ratio is not improved. Therefore, the sensor circuit must be refined and simple. If one resistor or capacitor can be saved, it must be removed. This is a problem that is easily ignored by many engineers who design sensors. It is known that with the problem of noise, the sensor circuit becomes more and more complex and becomes a strange circle.

3. Power consumption. The sensor is usually at the front end of the subsequent circuit, which may require a long lead connection. When the power consumption of the sensor is large, the connection of the leads will introduce all unnecessary noise and power supply noise, which makes the subsequent circuit more difficult to design. How to reduce the power consumption is also a big test in the case of small enough.

4. Selection of components and power circuit. The selection of components must be sufficient, as long as the device indicators are within the required range, the rest is the circuit design. Power supply is a problem that must be encountered in the design process of sensor circuit. Don't pursue the unattainable power index, but choose an op amp with good common mode rejection ratio. The most common switching power supply and devices designed with differential amplifier circuit can meet your requirements. The decoupling of the power supply must be designed reliably and comply with the requirements of the device manual.