The design of a good sensor is the result of experience plus technology. It is generally understood that a sensor is a description that converts a physical quantity into a physical quantity that can be expressed in another intuitive way through a circuit. For example, it is converted into higher voltage and current signals that only depend on the measured physical quantity, and then displayed. Therefore need to pay attention to a few points:
1. The measured physical quantity is generally very small, usually with inherent conversion noise as the physical conversion element of the sensor. For example, the signal strength of the sensor at 1 magnification is 0.1 ~ 1uV, and the background noise signal at this time also has such a large level that it even annihilates it. How to take out the useful signal as much as possible and suppress the noise is the primary problem for the sensor design.
2. The sensor circuit must be simple and refined. Imagine an amplifier circuit with a 3-stage amplifier circuit and a 2-stage active filter that amplifies the signal while amplifying the noise. If the noise does not deviate significantly from the useful signal spectrum, the two will be amplified simultaneously regardless of the filter. The signal-to-noise ratio has 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 many engineers who design sensors easily overlook. The known situation is that the sensor circuit is troubled by the noise problem, and the more modified the circuit is, the more complicated it becomes.
3. Power consumption problem. The sensor is usually at the front end of the subsequent circuit and may require longer lead connections. When the power consumption of the sensor is large, the connection of the leads will introduce all unnecessary noise and power supply noise, making the subsequent circuit more difficult to design. How to reduce power consumption when it is small enough is also a big test.
4. Selection of components and power supply circuit. The selection of components must be good enough, as long as the device index is within the required range, the rest is the circuit design problem. The power supply is a difficult problem that must be encountered in the sensor circuit design process. Do not pursue unreachable power specifications. Instead, choose an op amp with a good common-mode rejection ratio. The use of differential amplifier circuits may be the most common switching power supply and The device can meet your requirements. The decoupling of the power supply must be designed reliably, and follow the requirements of the device manual.
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