Homework#5 for Microelectronics (I)

Transcription

1 Homework#5 for Microelectronics (I) Sections:5.5,5.6,5.7 Deadline:1 月 3 日 ( 四 ) 課堂上繳交 provided by 陳旻珓助教 5.82 The pnp transistor in the circuit of Fig has β = 50. Find the value for R C to obtain V C = 4 V. What happens if the transistor is replaced with another having β = 100? Fig A circuit that can provide a very large voltage gain for a high-resistance load is show in Fig Find the value of I and R B to bias the BJT at I C = 2 ma and V C = 1.5 V. Let β = 90. Fig The circuit in Fig provides a constant current I O as long as the circuit to which the collector is connected maintains the BJT in the active mode. Show that VCC IO = α R [ R /( R + R )] E 2 + ( R R )/( β + 1) V BE Fig. 5.98

2 5.105 A pnp BJT is biased to operate at I C = 1.0 ma. What is the associated value of g m? If β = 50, what is the value of the small-signal resistance seen looking into the emitter (r e )? Into the base (r π )? If the collector is connected to a 3-kΩ load, with a signal of 2-mV peak applied between base and emitter, what output signal voltage results?

3 5.112 The transistor amplifier in Fig (a) is biased with a current source I and has a very high β. Find the dc voltage at the collector, V C. Also, find the value of g m. Replace the transistor with the simplified hybrid-π model of Fig (b) (note that the dc current source I should be replaced with an open circuit). Hence, find the voltage gain v c /v i. Fig (a) Fig (b)

4 5.115 For the circuit shown in Fig , draw a complete small-signal equivalent circuit utilizing an appropriate T model for the BJT (use α = 0.99). Your circuit should show the values of all components, including the model parameters. What is the input resistance R in? Calculate the overall voltage gain (v o /v sig ). Fig 5.115

5 5.116 In the circuit shown in Fig , the transistor has a β of 200. What is the dc voltage at the collector? Find the input resistance R ib and R in and the overall voltage gain (v o /v sig ). For an output signal of ±0.4 V, what values of v sig and v b are required? Fig

6 5.122 When a collector of a transistor is connected to its base, the transistor still operates in the active region because the collector-base junction is still in effect reverse biased. Use the simplified hybrid-π model to find the incremental resistance of the resulting two-terminal device.

7 5.124 The transistor in the circuit shon in Fig (a) is biased to operate in the active mode. Assuming that β is very large, find the collector bias current I C. Replace the transistor with the small-signal equivalent circuit model of Fig (b). Analyze the resulting amplifier equivalent circuit to chow that vo 1 RE = v R + r i v v o2 i E E e αrc = R + r Find the values of these voltage gain (for α = 1). Now if the terminal labeled vo1 is connected to ground, what does voltage gain v o2 /v i become? e Fig (a) Fig (b)

8 5.128 A common-emitter amplifier of the type shown in Fig is biased to operate at I C = 0.2 ma and has a collector resistance R C = 10 kω. The transistor has β = 100 and a large V A. The signal source is directly coupled to the base, and C C1 and R B are eliminated. Find R in, the voltage gain A vo, and R o. Use these results to determine the overall voltage gain when a 10-kΩ load resistor is connected to the collector and the source resistance R sig = 10 kω. Fig

9 5.130 For the common-emitter amplifier shown in Fig , let V CC = 9 V, R 1 = 27 kω, R 2 = 15 kω, R E = 1.2 kω, and R C = 2 kω. The transistor has β = 100 and V A = 100 V. Calculate the dc bias current I E. If the amplifier operates between a source for which R sig = 1 kω and a load of 3 kω, replace the transistor with its hybrid-π model, and find the value of R in, the voltage gain v o /v sig, and the current gain i o /i i. Fig

10 5.137 The BJT in the circuit of Fig has β = 100. (a) Find the dc collector current and the dc voltage at the collector. (b) Replacing the transistor by its T model, draw the small-signal equivalent circuit of the amplifier. Analyze the resulting circuit to determine the voltage gain v o /v i. Fig

11 5.139 Consider the CB amplifier of Fig with R L = 2 kω, R C = 3 kω, V CC = 5 V, and R sig = 100 Ω. To what value must I be set in order that the input resistance at E is equal to that of the source (i.e., 100 Ω)? What is the resulting voltage gain from the source to the load? Assume β is infinite. Fig

12 5.144 For the emitter follower in Fig , the signal source is directly coupled to the transistor base. If the dc component of v sig is zero, find the dc emitter current. Assume β = 100. Neglecting r o, find R in, the voltage gain v o /v sig, the current gain i o /i i, and the output resistance R out. Fig