Sensor Circuit Design Considerations

It is generally understood that a sensor is a circuit that converts a physical quantity through a circuit into a description that can be expressed in another intuitive, physical quantity. For example, the signal is converted to a higher voltage/current signal that depends only on the measured physical quantity and then displayed. Therefore need to pay attention to several points:

1, the sensor circuit must be simple and refined. Envisage an amplifying circuit with a 3-stage amplifying circuit with a 2-stage active filter, which amplifies the signal and also amplifies the noise. If the noise is not significantly deviated from the useful signal spectrum, no matter how the two filters are simultaneously amplified, the result The signal to noise ratio has not improved. Therefore, the sensor circuit must be refined and simple. Can save 1 resistor or capacitor must be removed. This is a problem that many engineers designing sensors easily overlook. The known situation is that the sensor circuit is plagued with the problem of noise, and the more complex the circuit is, the more complicated it becomes, and it becomes a vicious circle.

2. The physical quantity measured in general is very small, and usually also has the conversion noise inherent to the physical conversion element of the sensor. For example, the signal intensity of the sensor at the magnification of 1 is 0.1~1uV. At this time, the background noise signal has such a large level, and even annihilates it. How to remove the useful signal as much as possible and suppress the noise is the most important problem for the sensor design.

3, the selection of components and power circuit. The selection of components must be sufficient, as long as the device specifications are within the required range, and 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 power supply targets that cannot be achieved. Instead, select an op amp with a good common-mode rejection ratio and use the differential amplifier circuit design to design the most common switching power supply. The device will meet your requirements. The decoupling of the power supply must be a reliable design, and follow the requirements of the device manual, rather than less.

4, power consumption. Sensors are usually at the front of subsequent circuits and may require longer lead connections. When the power consumption of the sensor is large, the connection of the leads will introduce all the unnecessary noise and power noise to make the subsequent circuit more difficult to design. How to reduce power consumption in a small enough situation is also a big challenge.