Summary of "Electronic basics" • Analog circuit notes

Analog Circuit Basics

by Ajmer Zhiyuan

Information

#. Transistor effect

The main function of the transistor is the current amplification, in the case of a common emitter (signal from the base input, from the collector output, emitter grounding), when the base voltage UB has a slight change, the base current IB will also have a small change, under the control of the base current IB, the Collector current IC will have a big change, The larger the base current IB, the larger the collector current IC, on the other hand, the smaller the base current, the smaller the collector current, which is the change of the base current control collector current, but the change of the collector current is much larger than the base current, which is the amplification of the transistor, The ratio of changes in the IC to that of the IB is called the magnification of the transistor, and the magnification of the transistor is typically between dozens of and hundreds of times times.

The second function is the switch function, the shape of the switch transistor is the same as the general transistor shape, mainly for the circuit of the switch off and pass. Because it has the function of complete circuit breaker or switch-on, it is widely used in switching circuit, and has the characteristics of fast switching speed and long life, and is widely used in power supply, voltage regulator circuit, driving circuit, oscillation circuit, power amplification circuit, pulse amplifying circuit and line output circuit. Switching transistor due to the different power can be divided into small power switch and high-power switching tube.

#. FET is a voltage control element, while the transistor is a current control element. In the case of only allowing less current from the signal source, the field-effect tube should be chosen, and the transistor should be chosen under the condition that the signal voltage is low and the signal source is allowed to take more current.

I. Basic knowledge of amplification circuit

#. Analog signal: The characteristic of analog signal is that it is continuous in time and amplitude, and may take arbitrary value in a certain dynamic range.

In signal analysis, the signal is divided into 4 categories according to the continuity and dispersion of time and amplitude:

1) time continuous, numerical continuous signal 2) time discrete, numerical continuous signal 3) time discrete, numerical discrete signal 4) time continuous, numerical discrete signal wherein the 1th class is the analog signal

#. Digital circuit systems, which cannot process analog signals, need to be digitally converted, i.e. discretized or quantified. The first step in the conversion is to sample the analog signal, and the second step is to convert the sampled signal to a digital converter, which is implemented by A/D converter.

#. Analog signal amplification reason. Electrical signals from sensors that detect external physical signals are usually very faint. Signals that are too faint for these energies cannot be directly displayed and are generally difficult to analyze further; if the signal is digitized, the signal must be amplified to the volts magnitude to be accepted by a general ADC.

#. Depending on the actual input signal and the desired output signal is voltage or current, the amplification circuit can be divided into four types, namely: voltage amplification, current amplification, transimpedance amplification (the current is converted to the voltage output with the change) and the mutual amplifier (the voltage signal is converted to the corresponding change of the current output).

#. Controlled voltage Source: is a non-independent voltage signal source, its output is controlled by another signal, and with the signal linearly varying.

#. The output resistor of the ideal voltage amplification circuit should be 0 to minimize the attenuation of the signal, and the other link of signal attenuation in the input circuit, the signal source resistance and the amplifier circuit input resistor, here is required to improve the voltage amplification circuit input resistance, ideal voltage amplification circuit input resistance should be infinite.

#. The voltage amplification circuit is suitable for occasions where the internal resistance of the signal source is small and the load resistance is large.

#. Controlled Current Source: is another controlled signal source

#. Current amplification circuit is generally applicable to the situation where the resistance of the signal source is large and the load resistance is small.

#. The above four circuit models can achieve arbitrary conversion between each other, a practical amplifier circuit in principle can take four of the circuit model as its circuit model, but according to the nature of the signal source and load requirements, generally only one of the models in the circuit design or analysis of the concept of the most clear, the most convenient to use.

#. Amplification Circuit Input Indicator

Input resistance: The size of the input resistor determines the magnitude of the signal amplitude that the amplification circuit draws from the signal source. r=v/i. For the input voltage signal amplification circuit, that is, voltage amplification and mutual conduction amplification, the greater the r, the larger the input of the amplifier circuit of the greater V; Conversely, the input is a current signal amplification circuit, that is, current amplification and mutual resistance amplification, the smaller the R, the larger the input current amplification circuit.

Output resistor: The size of the output resistor determines its ability to carry the load. Output is a voltage signal amplification circuit, that is, voltage amplification and mutual resistance amplification, the smaller the R, the change of load resistance to the output voltage, the smaller the effect of this situation, the output power is generally low, the power supply power consumption is also low, more for the signal of the preamplifier and intermediate amplification, the output is a current signal amplification circuit, That is, the current amplification and mutual amplifier, and the controlled current source in parallel with the R, the change in load resistance to the output current of the smaller the impact, the output power is larger, the power supply is also large, usually used in the output stage of the electronic system, can serve as a variety of output physical variable converter drive circuit.

Gain: Voltage gain, current gain, transimpedance gain, mutual-conduction gain, which actually reflects the ability of the amplification circuit to convert power supply energy into signal energy under input signal control.

Frequency response and bandwidth: There are always some reactance elements in the actual amplification circuit, such as capacitance, inductance, the capacitance of electronic devices and wiring capacitance and wiring inductance, so the relationship between the output and input of the amplifier circuit must be related to the signal frequency. The frequency response of the amplified circuit refers to the steady-state response of the output in the case of an input sinusoidal signal with continuous changes in frequency.

#. Direct-coupled amplification circuit: Some amplification circuit frequency response, if the flat portion of the region has been extended to the DC, that is, the lower frequency is zero, this amplification circuit is called DC (direct coupling) amplification circuit. Most modern analog integrated circuits are amplified by direct coupling.

#. Amplitude Distortion: bandwidth constrained, the fundamental gain is large, and the two harmonic gain is small, so the output voltage waveform produces distortion

#. Phase distortion: The amplification circuit produces a phase shift to different frequency signals and also produces distortion.

#. Frequency Distortion | Linear distortion: Regardless of the spectral function or phase spectrum function changes, the corresponding time function waveform will be distorted, amplitude distortion and phase distortion is always called frequency distortion, they are caused by linear reactance element, so called linear distortion

#. In order to limit the frequency distortion of the signal to the extent permissible, it is required to correctly estimate the effective bandwidth of the signal when designing the amplification circuit, that is, the spectral width of the main energy or information of the signal, in order to match the bandwidth of the amplification circuit with the signal bandwidth.

Two. Semiconductor diodes and their basic circuitry

2.1 Basic knowledge of semiconductors

#. Semiconductor Materials: Silicon is one of the most commonly used semiconductor materials, and when the semiconductor is stimulated by external light and heat, its conductivity will change significantly, adding trace impurities in pure semiconductors, its conductivity will also increase significantly

#. Intrinsic semiconductors: A completely pure, structurally complete semiconductor crystal

Valence electrons: electrons in the outermost atom orbit, the chemical properties of the substance are determined by the valence electrons, and the semi-conductive properties are also related to valence electrons, so valence electrons are the object of our study.

#. Intrinsic semiconductors: A completely pure, structurally complete semiconductor crystal. The important physical characteristic of a semiconductor is its conductivity, which is related to the number of charge carriers contained in the unit volume within the material. The higher the concentration of charge carrier, the higher the conductivity.

#. The presence of holes is an important feature of semiconductors that differ from conductors

The direction of the hole movement and the direction of the electron movement are reversed, so that the current generated by the hole movement can be used to represent the current generated by the bound electron movement.

#. The root cause of the current generated by a hole or bound electron movement in a covalent bond is caused by the presence of a hole in the covalent bond. Only when a hole in the covalent bond occurs does it begin to conduct electricity.

# The greater the number of carriers in the semiconductor, the greater the resulting current

#. Impurity semiconductors can be divided into two major categories: Hole (P) type semiconductor and electronic (N) type semiconductor.

#. P-type semiconductor: mixed with a small amount of three-valence element impurity, which formed a covalent bond with the surrounding silicon atoms, resulting in a vacancy in the crystal due to the absence of an electron; in the P-type semiconductor, the hole number is much larger than the free electron number, in this kind of semiconductor, the hole is conductive mainly, so the hole is the majority

#. N-Type semiconductor: electronic semiconductor or N-type semiconductor, in the N-type semiconductor, the electron is the majority carrier, the hole is a minority carrier, after adding impurities, the number of carriers has a considerable degree of increase

#. Semiconductor doping is the most effective way to improve the conductivity of semiconductors

The formation and characteristics of 2.2 PN Junction

#. PN Junction Formation: P-type semiconductor containing the main impurities, at room temperature, by the main impurities are ionized into positively charged holes and negatively charged by the main ions; n-type semiconductors contain donor impurities, at room temperature, the donor impurity is ionized to negatively charged electrons and positively charged donor ions.

#. The number of positive and negative charges in semiconductors is equal, and their effect is offset by each other, thus maintaining electrical neutrality.

#. In the combination of P-type semi-conductive and N-type semiconductors, the concentration difference of electrons and holes occurs at the junction of the vacancy. Electrons and cavities are electrically charged, and the result of their diffusion is that the electrical neutrality of the P and N regions is destroyed.

The ions in the semiconductor are electrically charged, but because of their physical structure, they cannot move arbitrarily and therefore do not participate in conducting electricity. These electrically charged particles, which cannot be moved, are often referred to as space charges, which are concentrated near the junction of P and N, forming a very thin space charge area, known as the PN Junction.

In the space charge area, an electric field is formed, which is directed from the positive n-zone to the negatively charged P-zone, called the internal electric field. The direction of the internal electric field is to stop the spread of

The result of drift motion is the narrowing of the space charge area, which acts just as opposed to the diffusion motion.

#. Diffusion movement and drift movement are interrelated and contradictory, diffusion makes space charge area widen, electric field is enhanced, the resistance to majority carrier diffusion increases, but the drift of minority carrier is enhanced, and the drift makes the space charge area narrow, the electric field weakens, and the diffusion is easy to carry out. When the drift motion is equal to the diffusion motion, it is in a dynamic equilibrium state.