Project: - Active load

Transcription

1 Project: - Active load Objective: This project will show how the use of an active load in a common emitter amplifier can affect the gain open loop gain. Components: 2N2222, (2) 2N3906. Introduction: We have added to the common emitter design negative feedback in the bias circuit to stabilize the bias of the transistor. Rb1 and Rb2 with Cfdc to form the DC negative feedback path. Rb1, Rb2, and Rb3 with the voltage Vce form the voltage divider to bias the transistor Q-point. This is needed because we did not use an emitter resistor to control Ic and provide negative feedback in the DC bias circuit. The selection of the Cfdc needs to set the high frequency cutoff of the feedback network below the amplifier low frequency cutoff. Set Rb1 = Rb2 in your design. Set the current through Rb1and Rb2 to 10 * Ib. Set the current though Rb3 to 9 * Ib. For the AC design assume that the mid point of the feedback network is a ground at the midband frequency. This means that Rb2 is in the input impedance design and Rb1 is in the output impedance design. Design and prelab: Show all work, include schematics, plots and calculations. Common emitter without active load. Include design of all values of components. You must calculate Av, Ai, F L,, Rin, Rout, Cin, Cout for the transistor calculate r π,vb, Vc, Ve, Vce, Ic Circuit figure 1. Q1 = 2N2222 Assume Vbe = 0.7Vdc, β = 150 r o = 80kΩ Vout = 2Vpeak Set Ic1 = 3ma Rload = 1.5k Cfdc = 4.7uf Make Rb1 = Rb2 Rs = combined resistance of Rgen=50 Rfilter= 100 and Ri = 47. Low frequency cut off F L = Hz Simulate your design in Pspice. Include drawings, Transient plot and AC sweep plot. Calculate the Av = Vload / Vin from pspice plots and low frequency cutoff and high frequency cutoff. Mark on plots F L, F H, and Bandwidth. Spring: of 7

2 +9Vdc Cfdc Rc Rb1 Vout Cout Rb2 Rs Vin Cin Q1 NPN Rload AC Rb3 Rout Rin Figure 1. BJT CE amplifier Design common emitter with active load. Include design of all values of components. You must calculate Av, Ai, F L,, Rin, Rout, Cin, Cout for transistor Q1 calculate r π,vb, Vc, Ve, Vce, Ic. Hint: use the same bias design as the first design: Rb1, Rb2, and Rb3. Circuit figure 2. Q1= 2N2222 Q2, Q3 = 2N3906 Asume Vbe =0.7Vdc, β = 150, r o = 80kΩ Vout = 2Vpeak Set from the current source Ic1 = 3ma Rload = 1.5K Cfdc = 47uf. Assume the impedance of the active load is 80kΩ as seen from the collector of Q1. Remember the r 0 =80kΩ for Q1. Spring: of 7

3 Do not change the design of the bias resistors from the first case. Keep Rb1,Rb2 Rb3 and Vce the same. Make Rb1 = Rb2 Rs = combined resistance of Rgen=50 Rfilter= 100 and Ri = 47. Low frequency cut off = Hz Make Re2 = Re3 Set voltage across Re2, Re3 = 1Vdc. Design the current source to provide a current of 3ma into the collector of Q1. Simulate your design in Pspice. Include drawings, Transient plot and AC sweep plots. Calculate the Av = Vload / Vin from Pspice plots and low frequency cutoff and high frequency cutoff. Mark on plots F L, F H, and Bandwidth. +9Vdc +9Vdc Re2 Re3 Q2 PNP Q3 PNP Cfdc Rb1 Rbias Rb2 Cout Rs Vin Cin Q1 NPN Vout AC Rb2 Rout Rload Rin Figure 2. BJT CE Amplifier with active load Spring: of 7

4 1/10 Voltage divider 470 Ω Low-pass filter Shunt resistor Input of amplifier 100 Ω 47 Ω Cin Function generator internal impedance 50 Ω 56 Ω Filter resistor.0047uf.0047uf Shunt resister used to measure input current Function generator voltage source AC Figure 3. Front end low-pass filter. Lab Procedure: Build the two amplifiers Note: Add the input high-pass filter and bypass the supplies with 0.1uF and uF capacitors. Construct the common emitter amplifier without active load. Figure 1. Use Vcc = +9Vdc. Construct the Front end low-pass filter with 10 : 1 voltage divider 1. Measure the Q-point of the transistor. 2. With the load resistor connected adjust the output voltage to 2Vpeak at the midband frequency. Measure Vin and Vout and calculate the voltage gain. Save the plot and print the input and output waveform. 3. Measure Rout at midband frequency. Rout =( Vov- Vload)/Iload Note check that the output signal Voc is not clipping if it is decrease the input signal to make your measurements. 4. Measure Rin at midband frequency. Rin = Vin/Iin where Iin = Vri/Ri 5.. Measure at midband frequency Av = Vload/Vin voltage gain and Ai = Iload/Iin current gain 6. Sweep the input signal 10Hz to 1 MHz. save plot and print. With the function generator set such that the output voltage is 2Vpeak. Mark on the frequency plot the F L (low frequency cutoff) F H (high frequency cutoff) and BW(band width). Spring: of 7

5 Construct the common emitter amplifier with active load. Figure 2. Use Vcc = +9Vdc. Construct the Front end low-pass filter with 10: 1 voltage divider. 1. Measure the Q-points of the transistors. 2. With the load resistor connected adjust the output voltage to 2Vpeak at the miodband frequency. Measure Vin and Vout and calculate the voltage gain. Save the plot and print the input and output waveform. 3. Measure Rout at midband frequency. Rout =( Vov- Vload)/Iload Note check that the output signal Voc is not clipping if it is decrease the input signal to make your measurements. 4. Measure Rin at midband frequency. Rin = Vin/Iin where Iin = Vri/Ri 5.. Measure at midband frequency Av = Vload/Vin voltage gain and Ai = Iload/Iin current gain 6. Sweep the input signal 10Hz to 1 MHz. save plot and print. With the function generator set such that the output voltage is 2Vpeak. Mark on the frequency plot the F L (low frequency cutoff) F H (high frequency cutoff) and BW(band width). Spring: of 7

6 Name: Partner: Date: Report : Common emitter amplifier with Rc. Component value use to build the circuit. Figure 1 Rc= Rload= Rb1= Rb2 Rb3= Cin= Cout= Cfdc= 4.7uF 1. measure the Q-pint of Q1. Vbe= Vce= Ic= calculated from Rc. 2. Adjust the input function generator such that the output voltage is 2Vpeak at the midband frequency. Include plot of Vin, and Vout Vgen= Vin= V out= Av=Vload / Vin= 3. Measure Rout. Vload= Iload= Voc= non-clipping Rout = (Voc Vloaf)/ Iload = 4. Measure Rin. Vin= V47 Iin= Rin= Vin/Iin = 5. Av= Vload / Vin = Ai= Iload / Iin = 6. Plot frequency response. Sweep the voltage input from 10Hz to 1mega Hz. Save plot and mark on plot the low frequency and high frequency cutoff. Calculate the band width. Fl = Fh BW = Print the plot and include in report. Spring: of 7

7 Name: Partner: Date: Common emitter amplifier with active load. Component value use to build the circuit. Figure 2. Rload= Rb1= Rb2 Rb3= Re2= Re3= Rbais= Cin= Cout= Cfdc= 47uF 1. Measure the Q-pint of Q1. Vbe= Vce= Ic= calulated from Rc. Measure the Q-pint of Q2. Vbe= Vce= Ic= calulated from Re2 Measure the Q-pint of Q3. Vbe= Vce= Ic= calulated from Re3 2. Adjust the input function generator such that the output voltage is 2Vpeak at the midband frequency. Include plot of Vin, and Vout Vgen= Vin= V out= Av=Vout/Vin= 3. Measure Rout. Vload= Iload= Voc= non-clipping Rout = (Voc Vloaf)/ Iload = 4. Measure Rin. Vin= V47 Iin= Rin= Vin/Iin = 5. Measure Av= Vload / Vin = Ai= Iload / Iin = 6. Plot frequency response. Sweep the voltage input from 10Hz to 1mega Hz. Save plot and mark on plot the low frequency and high frequency cutoff. Calculate the band width. Fl = Fh BW = Print the plot and include in report. Before you leave: Shut down Windows, return cables to racks, return parts to correct drawer bins, return adapters to container, turn off bench power, clear bench, and place seat under bench. (5 points) Spring: of 7