Circuit noise - electrical performance test

Date：2021-11-02 16:19:32Views：2199

For the nominal noise in electronic circuits, it can be generally considered that it is a general term for all signals except the destination signal. At first, people called the electronic signals that caused the noise emitted by audio equipment such as radios noise. However, the consequences of some non purposeful electronic signals on electronic circuits are not all related to sound. Therefore, people gradually expanded the concept of noise. For example, those electronic signals that cause day shift stripes on the video screen are also called noise. It may be said that all signals in the circuit other than the target signal, whether it affects the circuit or not, can be called noise.

The term interference is often used in electronics, which is sometimes confused with the concept of noise. In fact, it is different. Noise is an electronic signal, and interference refers to a certain effect, which is an adverse reaction to the circuit caused by noise. There is noise in the circuit, but there is not necessarily interference. In digital circuits. It can often be observed with an oscilloscope that it is undesirable to mix some small spikes on the normal pulse signal, but a kind of noise. However, due to the circuit characteristics, these small spike pulses will not affect the logic of the digital circuit and cause confusion, so it can be considered that there is no interference.

When a noise voltage is large enough to interfere with the circuit, the noise voltage is called interference voltage. The maximum noise voltage applied by a circuit or a device when it can still maintain normal operation is called the anti-interference tolerance or immunity of the circuit or device. Generally speaking, the noise is difficult to eliminate, but we can try to reduce the intensity of the noise or improve the immunity of the circuit so that the noise will not form interference.

Introduction to noise types

Thermal noise (or Johnson noise or white noise) is directly related to the temperature reflected by the thermal disturbance of electrons in the resistance. In the case of a speaker or microphone, the noise source is the thermal movement of air molecules.

Shot noise is caused by random fluctuations of a large number of charged carriers emitted from the surface or diffused from the node. The noise is always associated with the DC current and independent of temperature. It mainly exists in bipolar transistors.

Scintillation noise (or 1 / f noise or pink noise) is mainly caused by silicon surface contamination and lattice defect related traps. These traps randomly capture and release carriers and have process related time constants, resulting in noise signals with energy concentrated at low frequencies.

The generation of frying noise (popcorn noise) is due to the contamination of heavy metal ions, which can be found in some integrated circuits and separation resistors. In some bipolar integrated circuits, the explosion noise is caused by too much doping in the emission region. Reducing the doping level may completely eliminate the frying noise. This is another type of low frequency noise.

Avalanche noise is a kind of noise produced by Zener phenomenon or avalanche breakdown phenomenon in PN junction. When avalanche breakdown occurs, holes and electrons in the depletion layer of reverse biased PN junction collide with silicon atoms to obtain enough energy to produce hole electron pairs.

TDMA noise ("hum") originates from the 217hz frequency waveform generated in the GSM cellular phone. When it is coupled to the audio path and transmitted to the speaker, earpiece or microphone, it will produce audible noise.

Noise test method

The performance of integral average sound level meter or automatic environmental noise monitoring instrument with accuracy of type 2 or above shall comply with the provisions of gb3785 and GB / T 17181 and be calibrated regularly. Use an acoustic calibrator to calibrate the measuring instrument before and after measurement, and the indication deviation of the measuring instrument shall not be greater than 0.5 dB, otherwise the measurement is invalid. The acoustic calibrator shall meet the requirements of GB / T 15173 for level 1 or level 2 acoustic calibrators. The microphone shall be equipped with a wind shield during measurement.

According to the monitoring object and purpose, the following three measuring point conditions (referring to the location of the microphone) can be selected to measure the ambient noise:

1. General outdoor

Measure at least 3.5 m away from any reflector (except the ground) and more than 1.2 m above the ground. If necessary, it can be placed on a high-rise building to expand the monitoring sound receiving range. The microphone shall be fixed at the height of 1.2m at the top of the vehicle.

2. Outdoor noise sensitive buildings

Outside noise sensitive buildings, 1 m from walls or windows and more than 1.2 m from the ground.

3. Indoor noise sensitive buildings

At least 1 m away from the wall and other reflective surfaces, about 1.5 m away from the window, and 1.2 m ~ 1.5 m high from the ground.

Standard for circuit noise

ITU-T g.228 spanish-1993 measurement of circuit noise in cable system using uniform spectrum random noise load

ITU-T g.228 french-1993 measurement of circuit noise in cable system using uniform spectrum random noise load

ITU-T g.228-1993 measurement of circuit noise in cable system using uniform spectrum random noise load

ITU-T h.34-1989 frequency band redistribution of telephone type circuits between Telegraph and other services - Characteristics of impulse noise measuring instruments for non telephone signal line transmission - sound programs and television signals

ITU-T h.42-1989 telephone type circuit facsimile telegraph transmission series - Characteristics of impulse noise measuring instruments for non telephone signal line transmission - sound program and television signal transmission (Study Group XV)

ITU-T h.41-1989 telephone type circuit facsimile telegraph transmission - Characteristics of impulse noise measuring instruments for non telephone signal line transmission - sound program and television signal transmission (Study Group XV)

ITU-T j.16-1989 measurement of weighted noise in sound program circuits - line transmission without telephone signals - transmission of television and sound programs and other media (Study Group 15) 9

ITU-T h.43-1989 fax transmission of leased telephone circuit documents - Characteristics of impulse noise measuring instruments for non telephone signal line transmission - sound program and television signal transmission (Study Group XV)

ITU-T h.32-1989 simultaneous communication by telephone and Telegraph on telephone type circuits - Characteristics of impulse noise measuring instruments for non telephone signal line transmission - sound programs and television signals

ITU-T o.71-1988 impulse noise measuring equipment, telephone type circuit - Research Group 4 with specifications for measuring equipment 4 pages in total At the same time, as recmn h.13

ITU-T j.16 spanish-1988 measurement of weighted noise in sound program circuit

ITU-T j.16 french-1988 measurement of weighted noise in sound program circuit

ITU-T o.71 spanish-1988 noise measuring equipment for telephone type circuits

ITU-T g.228-1988 measurement of circuit noise in cable system by uniform spectrum random noise load international analog carrier system (Study Group 15) 11pp

ITU-T j.16-1988 measurement of weighted noise in sound program circuit

ITU-T o.71 french-1988 noise measuring equipment for telephone type circuits