Name: diode bias and small-signal response
Uploaded: 2024-07-08T13:20:19.000Z
Duration: 1 min 18 s
Channel: JoVE

다이오드 회로에서 DC 바이어스 전압은 저항기를 통해 다이오드 전류를 구동하여 전류-전압 특성 곡선에서 지수 동작을 나타냅니다.
시간에 따라 변하는 작은 신호가 도입되면 Q 포인트를 중심으로 하는 DC 바이어스 전압과 결합됩니다.
총 순간 다이오드 전류의 지수 항은 바이어스 전류와 신호 전류 모두에 기여합니다.
신호 전압의 진폭이 열 전압보다 현저히 작으면 다이오드는 특성 곡선의 짧고 거의 선형에 가까운 세그먼트 내에서 작동합니다.
이 소신호 근사치에서는 지수 항이 단순화됩니다.
결과적으로 다이오드 전류는 DC 바이어스 전류와 신호 전류의 합이 됩니다.
다이오드 소신호 컨덕턴스는 소신호 전압에 대한 소신호 전류의 비율로 정의되며, 이는 Q 지점에서 I-V 곡선에 대한 접선의 기울기에 의해 결정됩니다.
다이오드 소신호 저항 또는 증분 저항이라고 하는 다이오드 소신호 컨덕턴스의 역은 열 전압을 바이어스 전류로 나눈 값과 같습니다.

소신호 다이오드 모델

Small-signal Diode Model

회로에서 다이오드의 동작을 분석할 때 다이오드를 통과하는 전류와 다이오드를 통과하는 전압 사이의 관계는 특히 직류(DC) 바이어스 전압의 효과를 고려할 때 중요합니다. 적용되면 이 DC 바이어스는 다이오드의 전류-전압(I-V) 특성이 기하급수적인 동작을 나타내는 Q 포인트라고 하는 다이오드의 작동 포인트에 영향을 줍니다. 이 바이어스 위에 시간에 따라 변하는 작은 신호를 도입하면 이 Q 지점 주변의 변동에 대한 다이오드의 응답을 조사하는 데 도움이 됩니다.
<img alt="Figure 1" src="/files/ftp_upload/15717/15717_Figure_1.svg" style="height: 250px;">
이 추가 신호 전압의 진폭이 다이오드의 열 전압(V_T)보다 상당히 작게 유지되면 다이오드의 응답은 특성 곡선의 짧은 마디에서 선형으로 근사화될 수 있습니다. 소신호 근사라고 불리는 이 시나리오는 복잡한 지수 관계를 보다 관리하기 쉬운 선형 관계로 단순화하여 총 순시 다이오드 전류(i_D)를 일정한 바이어스 전류 i_D(DC)와 다양한 신호 전류 i_D(AC)의 합으로 볼 수 있도록 합니다. 
<img alt="Equation 1" src="/files/ftp_upload/15717/15717_Equation_1.svg" style="height: 24px;">
신호 전류를 신호 전압에 연결하는 척도는 전도율(mhos 단위로 측정)로 표현되며 다이오드 소신호 전도율이라고 합니다. Q점에서 I-V 곡선에 대한 접선의 기울기입니다. 반대로, 다이오드의 소신호 또는 증분 저항(rd)은 전도율의 반대입니다. 이는 전류의 작은 변화에 대한 다이오드의 저항을 측정하고 열 전압을 바이어스 전류로 나누어 계산합니다.
<img alt="Equation 2" src="/files/ftp_upload/15717/15717_Equation_2.svg" style="height: 46px;">

<img alt="Equation 3" src="/files/ftp_upload/15717/15717_Equation_3.svg" style="height: 46px;">
 이러한 매개변수는 특히 신호 증폭 또는 감쇠에 대한 정밀한 제어가 필요한 응용 분야에서 다이오드와 관련된 회로를 설계하고 분석하는 데 중요합니다.

다이오드 회로에서 DC 바이어스 전압은 저항을 통해 다이오드 전류를 구동하여 전류-전압 특성에서 지수 동작을 나타냅니다.

Education

교육

JoVE Core

Electrical Engineering

전기공학

Unit 1

제1단원

Diodes

다이오드

KEY TERMS AND CONCEPTS

주요 용어 및 개념

diode bias and small-signal response

Diode bias and small-signal response describe how a diode behaves when a steady DC voltage and a tiny changing signal act on the same circuit. The DC bias sets the diode’s operating point, or Q point. Around that point, the diode current and voltage follow an exponential I-V relationship.

A small time-varying signal can be added on top of the DC bias to study how the diode responds to small changes. When the signal voltage is much smaller than the thermal voltage, the diode’s behavior can be treated as linear over a short part of its curve. This is called the small-signal approximation.

With this approximation, the total diode current can be written as the sum of a constant DC part and a varying AC part. The signal current is linked to the signal voltage by the diode small-signal conductance, which is measured in mhos. This conductance is the slope of the tangent to the I-V curve at the Q point.

The inverse of conductance is the diode’s small-signal, or incremental, resistance, r d. It shows how much the diode resists small changes in current. It is found by dividing the thermal voltage by the bias current. These ideas are useful when analyzing and designing circuits that use diodes for signal amplification or attenuation.

Diode Bias and Small-Signal Response

the ideal diode

Ideal Diode I-V Curve and Rectification

An ideal diode is a simple model of a semiconductor diode used to show how current moves through circuits. A diode has two terminals. The anode is positive, and the cathode is negative. In this model, current can flow only in one direction. When a positive voltage is applied to the anode relative to the cathode, the diode is forward-biased. In that state, it conducts current. When the cathode is at a higher potential than the anode, the diode is reverse-biased. It then blocks current and acts...

diode: forward bias

Diode Current in Forward Bias

Diode current in forward bias depends on how the p-type and n-type regions are connected to a battery. When the p-type region is tied to the positive terminal and the n-type region to the negative terminal, the diode is forward-biased. This setup lowers the potential barrier inside the diode and lets current move easily from the p-type side to the n-type side. The current-voltage behavior of a forward-biased diode is described by its I-V characteristics. These characteristics depend on the...

diode: reverse bias

Diode Reverse Current and Breakdown

A diode in reverse bias blocks current flow and widens its depletion region. In this setup, the positive terminal of the power source connects to the n-type material, and the negative terminal connects to the p-type material. The reverse connection also raises the barrier potential, so current stays very small. The small reverse current is called leakage current. It comes mainly from minority charge carriers. At room temperature, once the reverse voltage is above the thermal voltage, the...

zener diodes

Zener Diode Voltage Regulation

Zener diodes are semiconductor devices used to hold voltage steady in reverse bias. In reverse breakdown, current flows into the cathode and makes it positive relative to the anode. This behavior is different from a conventional diode and is the reason Zener diodes are useful in voltage regulation. A Zener diode has a nearly vertical current-voltage, or I-V, curve above a threshold called the knee current. That shape lets it keep a fairly stable voltage over a wide range of currents.

modeling of diode forward characteristics

modeling-of-diode-forward-characteristics

Diode Forward Bias: I-V Curve and Models

Diode forward bias is analyzed with the current-voltage, or I-V, curve and two common circuit models. These models help describe how a diode behaves when current flows in the forward direction. They are useful for electronic circuit design and analysis. The exponential diode model is used when the source voltage rises above 0.5 volts. At that point, the diode current increases exponentially above the saturation current. The I-V curve shows this nonlinear response as the forward voltage...

small-signal diode model

Diode bias and small-signal response describe how a diode behaves when a steady DC voltage and a tiny changing signal act on the same circuit. The DC bias sets the diode’s operating point, or Q point. Around that point, the diode current and voltage follow an exponential I-V relationship. A small time-varying signal can be added on top of the DC bias to study how the diode responds to small changes. When the signal voltage is much smaller than the thermal voltage, the diode’s behavior can be...

modeling of diode reverse characteristics

modeling-of-diode-reverse-characteristics

Zener Diode Load-Line Modeling

Zener diode load-line modeling shows how a reverse-biased diode sets a steady voltage in a circuit. Zener diodes use reverse breakdown in a controlled way, so they can hold a fixed voltage across their terminals. This makes them useful for voltage regulation. When the reverse voltage rises above the Zener voltage, or VZ, the diode enters the breakdown region. In this region, the current-voltage, or I-V, curve becomes nearly vertical after the knee current, IZ, is reached. That means the...

half wave rectifier

Single-Diode AC to DC Conversion

Single-diode AC to DC conversion uses a half-wave rectifier to change alternating current into a unidirectional voltage. The circuit is simple. It uses one diode in series with a load resistor and an AC power source. The diode controls the current because it allows flow in only one direction. During the positive half-cycles of the AC input, the diode is forward-biased. When the input voltage is greater than the diode threshold, current flows and an output voltage appears across the load...

full wave rectifier

AC to DC Conversion with Full-Wave Rectifiers

A full-wave rectifier converts alternating current, or AC, into direct current, or DC. It is more efficient than a half-wave rectifier. The circuit usually uses a center-tapped transformer, two diodes, and a load resistor. The center-tapped transformer is the key part of the circuit. Its secondary winding is split into two equal voltages with opposite polarities. That split lets the rectifier use both halves of the AC input waveform. During the positive half-cycle of the AC signal, diode D1...

bridge rectifier

AC to DC Conversion with Bridge Diodes

A bridge rectifier converts alternating current (AC) into direct current (DC) using four diodes arranged in a bridge layout. It is used to turn both halves of the AC waveform into a single-direction output. That makes it an important part of many electronics circuits. During the positive half-cycle, diodes D1 and D2 conduct. Current then flows through the load resistor R. At the same time, D3 and D4 are reverse-biased, so they do not conduct. The action switches during the negative half-cycle.

clipper circuit

Dual Diode Wave Clipping

Dual diode wave clipping uses diodes and biasing batteries to reshape an AC signal. A clipper circuit is a wave-shaping device that changes waveform parts without changing the whole signal. It is commonly used in television and radar communication systems to improve waveform modulation in transmitters and receivers. A dual-clipper setup uses two ideal diodes, two biasing batteries, and a resistor connected in parallel. The circuit works by responding to the phase of the input AC signal. The...

clamper circuit

DC Restorer for Waveform Level Shifting

A clamper circuit, or DC restorer, shifts a waveform up or down by adding a DC level. It is a special form of rectifier circuit. In this setup, the output is taken across the diode instead of across the capacitor. The circuit works well with square wave inputs and other pulse signals. The diode direction lets the capacitor charge to the most negative peak of the input signal. After that, the diode stops conducting. The capacitor then holds that voltage at a steady value. As a result, the...

voltage doubler circuit

How a Voltage Doubler Raises AC Output

A voltage doubler circuit raises the output voltage by using a clamping section and a rectifier section. The clamping section includes a capacitor, C1, and a diode, D1. The rectifier section includes a second diode, D2, and a capacitor, C2. The circuit starts working when a sinusoidal input signal enters the clamping section. Under ideal conditions, this stage clamps the positive peaks at zero volts. It also lets the negative peak reach a magnitude that is twice the input amplitude. That...

schottky barrier diode

Fast Switching in Schottky Diodes

Schottky barrier diodes use a metal-semiconductor junction to control current flow. They are built by combining a metal layer with a moderately doped n-type semiconductor. This contact creates the Schottky barrier, which gives the diode its one-way current behavior. When the metal touches the semiconductor, charge transfer occurs. The Fermi levels of the two materials align, and a depletion region forms near the contact area. In an n-type semiconductor, this region contains uncompensated...

key terms and concepts

Learn how DC bias sets a diode Q point and how small AC signals can be modeled with conductance and incremental resistance for circuit analysis.

Diode Bias and Small-Signal Response | JoVE K12

JoVE Core Electrical Engineering offers easy-to-understand animated videos that cover fundamental concepts of electric circuits along with circuit analysis techniques. It incorporates first-order and second-order circuits using operational amplifiers and circuit transformation concepts. The inclusion of practical design examples and real-world applications through scientist-in-action videos adds significant educational value, making complex concepts accessible.

electrical engineering

Diode Bias and Small-Signal Response

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