전자회로실험 A+ 10주차 결과보고서(BJT Amp Biasing)

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1. Frequency Response of Common Emitter Amplifier

CE amplifier에서 VOUT 은 VIN 과 비교했을 때 Phase difference가 180도이다. VCE의 크기는 IC가 커지면 작아지고, IC가 작아지면 증가한다. VCE = VCC – IC*RC의 공식을 통해 확인할 수 있다. Bandwidth는 연속 주파수 집합에서 상한 주파수와 하한 주파수 간의 차이이다. 일반적으로 Hz 단위로 측정되며 상황에 따라 passband bandwidth, baseband bandwidth을 가리킨다. Passband bandwidth는 대역 통과 필터, 통신 채널 또는 신호 스펙트럼의 상한 하한 cutoff 간의 차이이다. Lowpass filter이나 baseband signal의 경우 대역폭은 upper cutoff 주파수와 동일하다. Bandwidth = fH – fL (in Hz) Cutoff frequency 또는 corner frequency는 회로의 전력 출력이 pass band에서 주어진 전력 비율로 떨어지는 주파수이다. 실험 결과를 통해 일정 주파수를 넘어가면, CE amplifier의 voltage gain이 감소한다는 것을 알 수 있다.
2. Emitter Bypass Capacitor

왜곡되지 않는 증폭을 얻으려면 입력 신호가 트랜지스터의 선형 영역에서 작동하도록 base bias를 조절해야 한다. 그렇지 않으면 출력이 saturation 또는 cutoff region에 있게 된다. 실험 결과를 통해 emitter bypass capacitor는 gain을 늘려주고 안정성을 높여준다는 것을 알 수 있다. CE가 존재하지 않으면 RE는 교류와 직류신호의 감소를 유발하고, 이는 증폭기의 AC Voltage Gain의 감소를 유발한다.
3. Input and Output Impedance

위 공식을 이용해 각각의 값을 구할 수 있었다. Power gain: 부하에 주어지는 신호 전력과, 입력 회로에 의해서 흡수되는 신호 전력과의 비로, 보통 데시벨로 나타낸다.

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1. Frequency Response of Common Emitter Amplifier

The frequency response of a common emitter amplifier is an important characteristic that determines the amplifier's performance across different frequencies. The frequency response is influenced by various factors, including the transistor's parameters, the biasing circuit, and the load impedance. At low frequencies, the amplifier's gain is typically constant, but as the frequency increases, the gain starts to roll off due to the parasitic capacitances and inductances within the circuit. This frequency-dependent gain is known as the amplifier's bandwidth. The bandwidth is an important specification that determines the range of frequencies the amplifier can effectively amplify without significant distortion. Understanding the frequency response of a common emitter amplifier is crucial for designing circuits that require specific frequency characteristics, such as audio amplifiers, radio frequency (RF) amplifiers, and various types of signal processing applications. By analyzing the frequency response, engineers can optimize the amplifier's performance and ensure it meets the desired specifications for a particular application.
2. Emitter Bypass Capacitor

The emitter bypass capacitor is a crucial component in a common emitter amplifier circuit. Its primary function is to provide a low-impedance path for the AC signal, effectively bypassing the emitter resistor. This allows the AC signal to be amplified without being attenuated by the emitter resistor, which would otherwise reduce the overall gain of the amplifier. The emitter bypass capacitor also helps to stabilize the amplifier's bias point, ensuring that the transistor operates in the desired region of its characteristic curve. Without the bypass capacitor, the emitter resistor would introduce degeneration, reducing the amplifier's gain and potentially causing instability. The size of the bypass capacitor is determined by the desired low-frequency response of the amplifier, as well as the impedance of the emitter resistor. A larger capacitor value provides better low-frequency performance, but it also increases the size and cost of the circuit. Careful selection of the emitter bypass capacitor is essential for optimizing the overall performance and stability of the common emitter amplifier.
3. Input and Output Impedance

The input and output impedance of a common emitter amplifier are crucial parameters that determine the amplifier's performance and its ability to interface with other circuit components. The input impedance of the amplifier is primarily determined by the base-emitter junction of the transistor, as well as any additional input circuitry, such as biasing resistors or source impedance. A high input impedance is desirable, as it minimizes the loading effect on the input signal and ensures that the amplifier can effectively amplify the input without significant attenuation. On the other hand, the output impedance of the amplifier is determined by the collector-emitter junction of the transistor, as well as any output circuitry, such as load resistors or impedance-matching networks. A low output impedance is preferred, as it allows the amplifier to effectively drive the load without significant voltage drop or power loss. The input and output impedance of the common emitter amplifier must be carefully designed to match the impedance of the input source and the load, respectively, in order to achieve optimal power transfer and minimize signal distortion. Understanding and properly managing the input and output impedance is crucial for the successful design and implementation of common emitter amplifier circuits in various electronic applications.

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