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Ch.4 Book Notes.md - # Microelectronic Circuits - Sedra...

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# Microelectronic Circuits -- Sedra Smith Book Notes## Ch. 4 Diodes- First study of non-linear circuits besides op-amp saturation and slew rate.- Fictitious Ideal Diode- Silicon Junction Diode- Analysis of Diode Circuits- Device modeling- This study will form the basis of modeling transistor operation in the next3 chapters### 4.1 The Ideal Diode-#### 4.1.1 Current Voltage Characteristic- The ideal diode is the most fundamental non-linear circuit element. It has acircuit diagram seen in a below with an i-v relationship described in b![]()- If a negative current is applied to this diode (from the + direction seen in a)no current will flow and the diode will act as an open circuit. Also if a negativevoltage is applied to this diode, no current flows either and the diode acts as anopen circuit this can be seen in c. Diodes operated in this mode are said to be**reversed biased**, or operated in the reverse direction. An ideal diode has zerocurrent when operated in this mode and is said to be **cut off** or **off**- When a positive current is applied to the diode (from the + direction seen in a)zero voltage drop occurs across the diode. Therefore the diode is acting as a shortcircuit. Diodes operated in this mode are said to be **forward biased** or operatedin the forward direction. When operated this way they are also said to be **turnedon** or **on**- It also needs to be noted that the external circuit must be designed to limit thecurrent throughout a conducting diode, and the reverse voltage across a cutoffdiode. This point is seen in Figure 4.2 above more clearly. In (a) the diode isobviously conducting therefore the voltage drop across the diode will be 0. In (b)the diode is cutoff therefore the diode behaves as an open circuit, i.e. nocurrent, and the voltage at the cathode relative to the grounded anode will beequal to the input voltage of 10V- Note the positive terminal of the diode is called the **anode** and the negativeterminal is called the **cathode**- It can also be seen from the i-v relationship in b that the diode is nonlinear.However it is referred to as **piecewise linear** because it is linear in thereversed biased mode but and in the forward biased mode, however a discontinuityarises once the voltage hits 0V. Therefore if it is used in an application whereit's only reverse or forward biased then the diode will technically be linear.#### 4.1.2 A Simple Application: The Rectifier- This is a fundamental application of the diode that takes advantage of it'sseverely nonlinear i-v relationship this the basic form of this circuit can be seenbelow![](-6320e2bee9a9/phpVufCJU.png)- Given a the sinusoidal input seen in b. Note that for positive voltages of thiswaveform the diode will act as a short circuit, seen in c, with an ideal voltagedrop of zero and Vo is equal to Vi. However, when the sinusoid oscillates furtherinto the negative voltages the diode then behaves like an open circuit, seen in d,

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Analysis of Diode Circuits

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