High Frequency Technique

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1 High Frequency Technique

2 Marchese Guglielmo Marconi [guʎe:lmo mar'ko:ni] (25 April 1874 – 20 July 1937) was an Italian inventor, best known for his development of a radiotelegraph system, which served as the foundation for the establishment of numerous affiliated companies worldwide. He shared the 1909 Nobel Prize in Physics with Karl Ferdinand Braun, "in recognition of their contributions to the development of wireless telegraphy".[1] Later in life, Marconi was an active Italian Fascist[2] and an apologist for their ideology (such as the attack by Italian forces in Ethiopia).

3 Schottky Diode -금속-반도체 접합면에서 생기는 Schottky barrier를 이용
A Schottky diode is a special type of diode with a very low forward-voltage drop. When current flows through a diode, it has some internal resistance to that current flow, which causes a small voltage drop across the diode terminals. A normal diode has between volt drops, while a Schottky diode voltage drop is between approximately – this lower voltage drop translates into higher system efficiency. A Schottky diode uses a metal-semiconductor junction as a Schottky barrier (instead of a semiconductor-semiconductor junction as in conventional diodes). This Schottky barrier results in both very fast switching times and low forward voltage drop. A Schottky barrier is a potential barrier formed at a metal-semiconductor junction which has rectifying characteristics, suitable for use as a diode. The largest differences between a Schottky barrier and a p-n junction are its typically lower junction voltage, and decreased (almost nonexistent) depletion width in the metal. Not all metal-semiconductor junctions form Schottky barriers. A metal-semiconductor junction that does not rectify current is called an ohmic contact. Rectifying properties depend on the metal's work function, the band gap of the intrinsic semiconductor, the type and concentration of dopants in the semiconductor, and other factors. Design of semiconductor devices requires familiarity with the Schottky effect to ensure Schottky barriers are not created accidentally where an ohmic connection is desired. -금속-반도체 접합면에서 생기는 Schottky barrier를 이용 -Forward bias voltage drop이 작다 : 0.15 ~ 0.45 -속도가 빨라서 high frequency 회로에 활용

4 Gunn Diode A Gunn diode, also known as a transferred electron device (TED), is a form of diode used in high-frequency electronics. It is somewhat unusual in that it consists only of N-doped semiconductor material, whereas most diodes consist of both P and N-doped regions. In the Gunn diode, three regions exist: two of them are heavily N-doped on each terminal, with a thin layer of lightly doped material in between. When a voltage is applied to the device, the electrical gradient will be largest across the thin middle layer. Eventually, this layer starts to conduct, reducing the gradient across it, preventing further conduction. In practice, this means a Gunn diode has a region of negative differential resistance. The negative differential resistance, combined with the timing properties of the intermediate layer, allows construction of an RF relaxation oscillator simply by applying a suitable direct current through the device. The oscillation frequency is determined partly by the properties of the thin middle layer, but can be adjusted by external factors. Gunn diodes are therefore used to build oscillators in the 10 GHz and higher (THz) frequency range, where a resonant cavity is usually added to control frequency. The resonator can be based on a waveguide, , , etc. Tuning is done mechanically, by adjusting the parameters of the resonator, or in case of YIG resonators by electric current. Gallium arsenide Gunn diodes are made for frequencies up to 200 GHz, gallium nitride materials can reach up to 3 terahertz. The Gunn diode is named for the physicist J.B. Gunn who, in 1963, produced the first device based upon the theoretical calculations of Cyril Hilsum. -고전압에서는, 전자들이 높은 에너지 준위로 가게 되는데, 이준위에 있는 전자들의 effective mass가 커서 속도가 느려진다. 이에 따라, 전도성이 줄어든다.

5 Tunnel Diode -PN junction에서 tunneling 효과를 이용
A tunnel diode or Esaki diode is a type of semiconductor diode which is capable of very fast operation, well into the microwave frequency region, by using quantum mechanical effects. It was invented in 1958 by Leo Esaki, who in 1973 received the Nobel Prize in Physics for discovering the electron tunneling effect used in these diodes. These diodes have a heavily doped p-n junction only some 10 nm (100 Å) wide. The heavy doping results in a broken bandgap, where conduction band electron states on the n-side are more or less aligned with valence band hole states on the p-side. Tunnel diodes were manufactured by General Electric and other companies from about 1960, and are still made in low volume today. [1] Tunnel diodes are usually made from germanium, but can also be made in gallium arsenide and silicon materials. They can be used as oscillators, amplifiers, frequency converters and detectors. [2] -PN junction에서 tunneling 효과를 이용

6 Amplification by Negative Resistance
-Vb : 전압을 negative resistance 영역(differential resistance = -r)으로 유지 -R < r -AC 신호에 대해서, Voltage divider로 생각해서 식을 세우면 -따라서, gain G = v0/vi는

7 Negative Resistance를 이용한 Resonator
-Kirchhoff's voltage loop rule에 따르면, -이 방정식의 해는, -r과 R 값에 따라서, r<R r=R r>R

8 Varicap Diode -다이오드에 reverse bias를 걸고 구동
In electronics, a varicap diode, varactor diode, variable capacitance diode or tuning diode is a type of diode which has a variable capacitance that is a function of the voltage impressed on its terminals. Varactors are principally used as a voltage-controlled capacitor, rather than as rectifiers. They are commonly used in parametric amplifiers, parametric oscillators and voltage-controlled oscillators as part of phase-locked loops and frequency synthesizers. Varactors are operated reverse-biased so no current flows, but since the thickness of the depletion zone varies with the applied bias voltage, the capacitance of the diode can be made to vary. Generally, the depletion region thickness is proportional to the square root of the applied voltage; and capacitance is inversely proportional to the depletion region thickness. Thus, the capacitance is inversely proportional to the square root of applied voltage. All diodes exhibit this phenomenon to some degree, but specially made varactor diodes exploit the effect to boost the capacitance and variability range achieved - most diode fabrication attempts to achieve the opposite. -다이오드에 reverse bias를 걸고 구동 -reverse bias의 크기가 커지면, depletion region의 두께가 두꺼워져서, capacitance가 줄어듦

9 Varicap 기반 Frequency Modulation
Oscillator 외부 신호로 varicap에 전압 -varicap을 포함한 Oscillator 제작 -오디오 등 낮은 주파수 신호를 이용하여 Varicap의 전압을 변화시켜서, Oscillation frequency 조절

10 라디오 신호 측정 : 광석 라디오 방송국 (고주파에 저주파 신호를 얹어서 방송) -안테나 : dipole wire
LC회로 (특정 주파수 선정) 마이크로폰 (저항) 반파 정류 Capacitor를 통해서 고주파를 없애버리는 Low Pass Filter 방송국 (고주파에 저주파 신호를 얹어서 방송) -안테나 : dipole wire -LC회로를 이용하여 특정 주파수 선정 -다이오드를 통해 반파정류 -RC회로를 통해 고주파 제거

11 Non-inverting amplifier
라디오 신호증폭 회로 라디오 신호 측정/정류/검파 회로 Non-inverting amplifier for AC

12 Transmission Line : Cable
Characteristic Impedance Z0=(L/C)1/2 L,C : inductance(capacitance)/length Coaxial cable : 50 ~ 100  Parallel conductor line : 300 ~ 100 

13 Characteristic Impedance of Transmission Line
Z0 = V/I (Z0가 크면, 신호전달(I)이 약함) -저항이 거의 없을 경우(R ~0, G large), Sinusoidal Wave를 가정하면, -저항이 있는 일반적인 경우

14 by the way 평면판 도체에서, 단위길이당 마찬가지로 평면판 전류 sheet에서 단위 길이당
따라서, impedance는 또한 로 쓰여질 수 있다.

15 Coaxial Cable -저항이 거의 없는 경우일지라도, AC 신호에 대한 impedance가 있을 수 있다.

16 Capacitance of Coaxial Cable

17 Inductance of Coaxial Cable
따라서 coaxial cable의 characteristic impedance는 50옴 정도!!