Question

Laboratory 2: Transistor circuit characteristics A. Objectives: 1. To study the basic characteristics of a transistor circuit. 2. To study the bias circuit of a transistor circuit. B. Apparatus: 1. DC Power supply 2. Experimental boards and corresponding components 3. Electronic calculator (prepared by students) 4. Digital camera (prepared by students for photo taking of the experimental results) 5. Laptop computer with the software PicoScope 6 and Microsoft Word installed. 6. PicoScope PC Oscilloscope and its accessories. 7. Digital multi-meter. C. Theoretical Background Transistors are wildly applied to many electronic applications in not only the amplifier circuit but also the digital switch circuits. Basically, transistors have three operation modes, namely, cutoff mode, saturation mode and active mode. In order to apply a transistor into an amplifier circuit, resistor networks are required in both input and output stages of the amplifier and biased the transistor into its active mode Figure1 depicts a typical transistor biasing circuit which is called common emitter amplifier. At the input stage of the amplifier, a voltage divider is used and the following circuit parameter can be calculated. Input equivalent resistance: RTh RR2 Input equivalent voltage: Eh -VocV Input base current:rtDRE -v By KCL, 12 At the output stage, a load line with the equation: VCEVcc c(Rc RE) can be constructed in the lc vs VCE graph. By fixing the base current lB and ß, the Q point of the transistor can be determined by finding the intercept of the load line and the corresponding characteristic curve as shown in Figure 2 After the transistor is biased in its action mode, the gain of the amplifier can be analysed by using the small signal equivalent circuit, shown in Figure 3. The voltage gain, input impedance and output impedance of the amplifier can be calculated by using the following equations. (1) Connect up the circuit shown in Figure 1 without any AC input. Measure the DC voltages: VB, Vc and VE, by using the digital multi-meter (2) By the results obtained in part (1), calculate the transistor parameters: 1, Ic, VBE, VCE, VBC and β using the equations provided in section C and other necessary equations. (3) Connect the signal generator to the amplifier input, and the CRO to the amplifier output. Adjust the voltage of the signal generator to sine wave, 0.25 V and frequency of 30 kHz. Capture the output waveform and hence measure the peak output voltage 4) By the results obtained in part (3), calculate the magnitude of the voltage gain (5) Repeat steps (3) and (4) when the bypass capacitor, i.e. 4.7 puF, at the emitter is removed H. Question (1) Comment on the experimental results with the theoretical calculations. (2) How is the voltage gain affected by the presence of the bypass capacitor? (3) Design a small signal common emitter amplifier using a npn transistor with ro of 2 MQ, re of 40 Ω and a gain of-150. Show your component values and calculations when necessary.

Answer 1

R, 22 Rth= 15-24 K-S- So Rit R2 牙*T 8.33-o. 8-33-D,斗 e. 1キイ HAL六

Lot h 니D Rc2 )200 m RcRe