深入了解电路噪声的那些事

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电路噪声

纹的那些电子信号也称为噪声。可能以说,电路中除目的的信号以外的一切信号,不管它对电路是否造成影响,都可称为噪声。例如,电源电压中的纹波或自激振荡,可对电路造成不良影响,使音响装置发出交流声或导致电路误动作,但有时也许并不导致上述后果。对于这种纹波或振荡,都应称为电路的一种噪声又有。某一频率的无线电波信号,对需要接收这种信号的接收机来讲,它是正常的目的信号,而对另一接收机它就是一种非目的信号,即是噪声。在电子学中常使用干扰这个术语,有时会与噪声的概念相混淆,其实,是有区别的。噪声是一种电子信号,而干扰是指的某种效应,是由于噪声原因对电路造成的一种不良反应。而电路中存在着噪声,却不一定就有干扰。在数字电路中,往往可以用示波器观察到在正常的脉冲信号上混有一些小的尖脉冲是所不期望的,而是一种噪声。但由于电路特性关系,这些小尖峰脉冲还不致于使数字电路的逻辑受到影响而发生混乱,所以可以认为是没有干扰。

当一个噪声电压大到足以使电路受到干扰时,该噪声电压就称为干扰电压。而一个电路或一个器件,当它还能保持正常工作时所加的最大噪声电压,称为该电路或器件的抗干扰容限或抗扰度。一般说来,噪声很难消除,但可以设法降低噪声的强度或提高电路的抗扰度,以使噪声不致于形成干扰。

电子电路中噪声的产生?如何抑制

XX这个东西主要是由于电路中的数字电路和电源部分产生的在数字电路中,普遍存在高频的数字电平,这些电平可以产生两种噪声:1,电磁辐射,就像电视的天线一样,通过发射电磁波来干扰旁边的电路,也就是你说的噪声0.2,耦合噪声,指数字电路和旁边的电路存在一定的耦合,噪声可以直接在电器上直接影响其他的电路,这种噪声更厉害。

电源上存在的噪声:如果是线性电源,首先低频的50Hz的就是一个严重的干扰源由于初级进来的交流电本身就不纯净,而且是波浪的正弦波,容易对旁边的电路产生电磁干扰,也就是电磁噪声。如果是开关电源的话噪声更严重,开关电源工作在高频状态,并且在输出部分存在很脏的谐波电压,这些对整个的电路都能产生很大的噪声。

防止方法:合理地接地,采用差分结构传输模拟信号,在电路的电源输出端加去耦电容,采用电磁屏蔽技术,模拟数字地分开,信号线两边走底线,地线隔离等等其实我说的这些在去除噪声的方面只是冰山一角,就算是玩了30年电子的人也不会完全掌握所有的这类技术,因为理解掌握这类东西需要很强的技术基础和相当丰富的经验,不过我告诉你的这些在大体上已经足够了。

本底噪声是由电路本身引起的,由于电源的不纯净,电路的相位裕度和增益裕度不合适等等电路本身和器件的原因。这部分需要在电路设计时进行改进。

其他噪声是由于电路布局布线不合理等等认为因素,电磁兼容,导线间干扰等等

XXThe elimination of analog circuit noise is more dependent on experience than on scientific basis. The situation that designers often encounter is that after the analog hardware part of the circuit is designed, it is found that the noise in the circuit is too large, and the design and wiring have to be re-designed. This "try it out" design approach will eventually succeed after several twists and turns. However, a better way to avoid noise problems is to follow some basic design guidelines and make use of noise-related fundamentals when making decisions early in the design process.

Design method of low noise preamplifier circuit

The role of the preamplifier in the audio system is critical. This article first explains how an engineer should properly select components when designing a preamplifier for a home audio system or PDA. Subsequently, a detailed analysis of the source of the noise provides guidelines for designing low noise preamplifiers. Finally, taking the preamplifier of the PDA microphone as an example, the design steps and related precautions are listed.

A preamplifier is a circuit or electronic device placed between a source and an amplifier stage, such as an audio preamp placed between a disc player and an advanced audio system power amplifier. The preamplifier is designed to receive weak voltage signals from the source. The received signal is first amplified with a small gain, sometimes even adjusted or corrected before being transmitted to the power amplifier stage, such as audio front. The amplifier can first equalize the signal and perform tone control. Whether it's a home audio system or a PDA design preamplifier, you have to face a very headache, which components should be used properly?

Component Selection Principles

Because of the small size and performance of op amp ICs, many of these preamplifiers use this type of op amp chip. When designing a preamplifier circuit for a sound system, we must clearly know how to select the appropriate specifications for the op amp. System design engineers often face the following issues during the design process.

xx1.是否有必要使用高精度运算放大器?

输入信号电平幅度可能超过运算放大器的误差容差,这对于运算放大器是不可接受的。如果输入信号或共模电压太弱,设计人员应使用具有极低补偿电压(Vos)和极高共模抑制比(CMRR)的高精度运算放大器。是否使用高精度运算放大器取决于系统设计所需的放大增益的次数。增益越大,运算放大器就越精确。

2.运算放大器需要什么样的电源电压?

此问题取决于输入信号的动态电压范围,系统的总电源电压和输出要求。然而,不同电源的不同电源抑制比(PSRR)会影响运算放大器的精度,该运算放大器基于电池供电系统。受影响最大。此外,功耗也与内部电路的静态电流和电源电压直接相关。

3.输出电压是否需要全摆幅?

低电源电压设计通常需要轨到轨输出,以利用整个动态电压范围来增加输出信号摆幅。至于轨到轨输入的问题,运算放大器电路的配置有其自己的解决方案。由于前置放大器通常配置有反相或非反相放大器,因此输入不需要全摆幅,因为共模电压(Vcm)始终小于输出范围或等于零(极少数例外情况,例如浮地接地单电源电压运算放大器)。

4.增益带宽问题更令人担忧吗?

件。

了解有关噪音的更多信息

在设计低噪声前置放大器之前,工程师必须仔细检查放大器的噪声。一般来说,运算放大器的噪声主要来自四个方面:

1. Thermal noise (Johnson): The thermal noise of the broadband characteristic due to the irregular fluctuation of the electron energy of the current in the electric conductor has a direct relationship between the square root of the voltage rms value and the bandwidth, the electrical conductor resistance and the absolute temperature. For resistors and transistors (such as bipolar and field effect transistors), such noise effects cannot be ignored because their resistance values are not zero.

2. Flicker noise (low frequency): Noise generated by the continuous generation or integration of carriers on the crystal surface. In the low frequency range, such flicker appears in the form of low frequency noise, which becomes "white noise" once it enters the high frequency range. The flicker noise is mostly concentrated in the low frequency range, causing interference to resistors and semiconductors, and the bipolar chip is more disturbed than the field effect transistor.

3. Shooting noise (Schottky): Schottky noise is generated by current carriers with particle characteristics in the semiconductor. The square root of the current is directly related to the average bias current and bandwidth of the chip. This noise has the characteristics of broadband.

4. Popcorn frequency: If the surface of the semiconductor is contaminated, it will produce such noise. The effect is as long as several milliseconds to several seconds. The cause of the noise is still unknown. Under normal circumstances, there is no certain pattern. The use of cleaner processes in the production of semiconductors can help reduce such noise.

In addition, since the input stages of different operational amplifiers adopt different structures, the difference in transistor structure makes the noise amount of different amplifiers greatly different. Below are two specific examples.

Noise of the bipolar input op amp: The noise voltage is mainly caused by the thermal noise of the resistor and the high-frequency shot noise of the input base current. The level of the low-frequency noise depends on the low-frequency noise generated by the base current of the input transistor flowing into the resistor. The noise current is mainly generated by the noise of the input base current and the low frequency noise of the resistor.

xxCMOS输入运算放大器噪声:噪声电压主要是由高频通道电阻的热噪声和低频区域的低频噪声引起的。 CMOS放大器的转角频率高于双极放大器的转角频率,宽带噪声远优于双倍放大器。极点放大器很高;噪声电流主要是由输入栅极泄漏的射击噪声引起的。 CMOS放大器的噪声电流远低于双极放大器的噪声电流,但每增加10(C)温度,噪声电流增加约40%。/P>

工程师必须先了解噪声问题并进行大量计算才能准确表示为数字。为了避免使问题复杂化,此处仅使用音频规范的最关键参数。

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上式中的S和N都是幂。

PDA麦克风前置放大器电路

在这里,我们将讨论如何为PDA设计麦克风前置放大器。如上所述,我们必须理解源是来自输入前置放大器的信号。首先,我们必须知道以下信息:

您计划使用的麦克风类型

?麦克风输出信号电平

麦克风阻抗和指定阻抗的频率

增益调节,增益可能受运算放大器增益带宽积的限制

?输入信号频率范围

?噪音规定

例如,陶瓷麦克风的技术规格如下:

阻抗:2.2k(以1kHz频率工作)

?输出信号:200(Vpp

?音频输入频率范围:100Hz至4kHz

热噪声:2nV /(Hz

The gain of the preamplifier is 500 (non-inverted), the first stage can achieve 5 times gain, and the second stage can achieve 100 times gain.

We quote Formula 1:

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Equal Input Noise (EIN)=Total Input Reference Noise () × Input Frequency Range

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Output noise=equal input noise × gain=545.81nV × 5=2.73uV (for level 1 gain) or 545.81nV × 100=54.58uV (for level 2 gain).

Total output noise of two amplifier stages

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Signal-to-noise ratio level of 1 volt output voltage=20 × log (1V ÷ 54.58uV) ≈ 85.3dB

The total output noise of the circuit is approximately the square root of the sum of the mean squared values of the root mean square of each noise source. In addition, the output noise is usually mostly from the source with the largest amount of noise. The actual circuit is shown in Figure 2.

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Figure 2 MIC preamplifier circuit diagram

Please note that this circuit is only suitable for single-supply designs where the input and output capacitors (C1 and C4) are optional and can be selected by the engineer based on actual conditions. Applicability depends on how the input and output of the user system are connected. If the microphone output is DC compensated, then a C1 input capacitor is required to block the DC signal. The output capacitor can also perform the same function.

xx目前市场上的大多数麦克风都基于2k(高阻抗麦克风和仅几百个(低阻抗麦克风)。两种类型的麦克风都可以使用上述前置放大器设计。高阻抗和高输出麦克风前置放大器更常见。可以使用简单的,非反相或反相放大器配置。由于其平坦的频率响应,无需专门化均衡,输入电平较大,放大器噪声要求低,但高 - 阻抗麦克风具有未知噪声。磁场非常灵敏。低阻抗,低输出麦克风前置放大器也可以使用同相或反相放大器放大输入信号,频率响应和均衡要求大致为与高阻抗,高输出前置放大器相同。麦克风的输出电平很低,工程师必须注意使用低噪声运算放大器。例如,具有更好性能的低噪声运算放大器应产生较低的输入参考电压噪声,噪声不应超过10nV /((Hz)。/P>

运算放大器电路中本征噪声的分析与测量

设备下面有多少噪音,并找到降低噪音和测量技术的方法,以准确确认其设计的可行性。

噪声包括固有噪声和外部噪声,这两者都会影响电子电路的性能。外部噪声来自外部噪声源,典型示例包括数字开关,60 Hz噪声和功率开关。本征噪声由电路元件本身产生,最常见的例子包括宽带噪声,热噪声和闪烁噪声。本系列文章将向您展示如何预测电路的固有噪声水平,如何使用SPICE仿真技术以及噪声测量技术。

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