Exercise 1: Shunt-Series Current Gain When you have completed this exercise, you will be able to calculate and measure shunt-series current oscilloscope. Resistor R sh provides shunt feedback to the input stage (Q1) while resistor R ef supplies series feedback to the output stage (Q2). The current gain (Ai) equals the shunt resistance (R sh ) divided by the series resistance (R ef ). Ai = R sh ef Festo Didactic 91567-P0 133
Using the given values of R sh and R ef, calculate the current gain. Ai = R sh ef Ai = (Recall Value 1) shown. All ac oscilloscope measurements and accompanying calculations are peak-to-peak (pk-pk) values, unless stated otherwise. Use ac coupling and x10 probes for these measurements. 134 Festo Didactic 91567-P0
Connect the oscilloscope channel 1 probe across output load resistor R11. Adjust the signal generator for a 100 mv pk-pk R11 = 100 V o = 100 mv pk-pk I o = V o I o = ma pk-pk (Recall Value 1) Unless otherwise indicated, all voltage and current readings and calculations are peak-to-peak values. Festo Didactic 91567-P0 135
Connect the oscilloscope channel 1 probe to the junction of C1 and R1, and connect the channel 2 probe to the base of Q1 (the other side of R1). Set both channels of the oscilloscope for ac coupling. oscilloscope channel 2 to INVERT. Measure the peak-to-peak signal voltage (V R1 ) across input resistor R1. V R1 = mv pk-pk (Recall Value 2) I R1 = V R1 I R1 = A pk-pk (Recall Value 3) Calculate the current gain of the circuit by using your measured values of I o ( ma pk-pk [Step 3, Recall Value 1]) and I i ( A pk-pk [Step 6, Recall Value 3]). Ai = I o i Ai = (Recall Value 4) 136 Festo Didactic 91567-P0
You can calculate current gain (Ai) by dividing the shunt feedback resistance (R5) by the series feedback resistance (R7). Using the given values of R5 and R7, calculate the circuit current gain. Ai = (Recall Value 5) Your measured current gain ( [Step 7, Recall Value 4]) and the current gain calculated from the shunt and series feedback resistors ( [Step 9, Recall Value 5]) are a. b. nearly the same. Verify that the output is still set for 100 mv pk-pk. Connect the oscilloscope channel 1 probe to the circuit input at C1, and measure the input signal voltage level. V i = mv pk-pk (Recall Value 6) Festo Didactic 91567-P0 137
V o = 100 mv pk-pk V i = mv pk-pk (Step 11, Recall Value 6) Av = V o i Av = (Recall Value 7) Is the circuit voltage gain much greater or less than the current gain? a. greater than b. less than Connect the oscilloscope channel 1 probe to the output across R11. to 110. You can turn CM 18 off and on by using the Toggle switch provided. 138 Festo Didactic 91567-P0
With CM 18 activated, measure the output signal level. V o = mv pk-pk (Recall Value 8) Calculate the output current with CM 18 activated. V o = mv pk-pk (Step 15, Recall Value 8) I o = V o I o = ma pk-pk (Recall Value 9) Calculate the current gain with CM 18 activated. The input current remains the same as what you measured before. I i = A pk-pk (Step 6, Recall Value 3) I o = ma pk-pk (Step 16, Recall Value 9) Ai = I o i Ai = (Recall Value 10) Make sure all CMs are cleared (turned off) before proceeding to the next section. in shunt with the input stage and in series with the output stage. sh ) to the series feedback resistor (R ef ) determines the current gain (Ai). Festo Didactic 91567-P0 139
1. Adjust the signal generator for an output of 100 mv pk-pk across R11. a. increases because the output increases. b. decreases because the output increases. c. decreases because the output decreases. d. increases because the output decreases. 2. a. b. c. d. None of the above 140 Festo Didactic 91567-P0
3. a. collector resistor (R6). b. base resistor (R1). c. emitter resistor (R4). d. ratio of the shunt resistor (R5) to the series resistor (R7). 4. A current gain of 250 is required, and the series feedback resistor (R7) value is 100. What is the value of the shunt resistor (R5)? a. 250 b. 1000 c. 25,000 d. 150 5. Removing bypass capacitor C4 increases the series feedback resistor value from 220 to a. 4120. b. 3.9 k. c. 41.2 k. d. 1000. Make sure all CMs are cleared (turned off) before proceeding to the next section. Festo Didactic 91567-P0 141