1. Single point grounding
The low operating frequency (<1MHz) adopts single point grounding (that is, one structural point in the whole circuit system is regarded as the reference point of grounding, all ground connection is connected to this point and a safety ground bolt is set) to prevent the electrical coupling of common ground impedance caused by two point grounding.The single point connection mode of multiple circuits can be divided into series connection and parallel connection. Because of the circuit coupling of the common ground impedance generated by the series grounding, it is better to adopt the single point grounding mode of parallel connection for the low-frequency circuits.In order to prevent the power frequency and other stray current from causing interference on the signal ground wire, the signal ground wire should be insulated from the power ground wire and the machine case ground wire.And only connect to the power ground wire, the chassis ground wire and the safety ground bolt of the ground wire (except floatation).
2. Multi-point grounding
With high operating frequency (>30MHz), multi-point grounding is adopted (i.e., in this circuit system, a ground plate is used to replace the ground loop of each part of the circuit).Because the inductive resistance of the ground lead is proportional to the frequency and length, the common ground impedance will be increased when the working frequency is high, so the electromagnetic interference caused by the common ground impedance will be increased, so the length of the ground wire is required to be as short as possible.When using multi-point grounding, try to find the nearest low resistance value ground grounding.
3. Mixed earth
The circuit with working frequency between 1 and 30MHz adopts mixed ground type.When the length of the grounding wire is less than 1/20 of the working signal wavelength, the single-point grounding is adopted; otherwise, the multi-point grounding is adopted.