RC Coupling When you have completed this exercise, you will be able to determine the frequency response of an oscilloscope. The way in which the gain varies with frequency is called the frequency response. T above 100 khz. 224 FACET by Lab-Volt
a. frequency response. b. bandwidth. c. gain. range has been reached. and 20 khz. a. 20 Hz to 100 Hz. b. 20 Hz to 100 khz. c. 20 khz to 100 khz. d. None of the above. FACET by Lab-Volt 225
RC Coupling The size of the coupling capacitor (C2) can affect frequency response at lower frequencies. The capacitive reactance (X C ) of a 1.0 F capacitor does not appreciably affect the magnitude of the second-stage ac input signal (V i2 ) at frequencies above 50 Hz. The second-stage input (V i2 o1 ). 226 FACET by Lab-Volt
F to 0.01 F), the capacitive reactance (X C ) increases by a factor of 100. If C2 is changed to 0.01 F, X C and the input impedance of Q2 act like a voltage divider, making V i2 o1 at frequencies less than 5 khz. with signals less than 5 khz a. decreases. b. increases. c. remains the same. FACET by Lab-Volt 227
RC Coupling stray capacitance in the circuit elements. The upper frequency limit of the bandwidth is affected by a. b. stray capacitance in the circuit elements. c. Both of the above. d. None of the above. R12 is connected to C4, but R11 is not connected to R10. Measure the supply voltage (V A ) with reference to ground. V A = Vdc (Recall Value 1) 228 FACET by Lab-Volt
While observing the signal on oscilloscope channel 1, adjust the sine wave generator for a 1 khz, 100 mv pk-pk ac input signal (V i1 ) at the base of transistor Q1. Connect the channel 2 oscilloscope probe to the second-stage ac output signal (V o2 ) at C4. Measure V o2 at a frequency of 1 khz. V o2 = mv pk-pk (Recall Value 2) Adjust the sine wave generator for 20 Hz, and if necessary, readjust the input signal (V i1 ) for 100 mv pk-pk. Measure V o2 at a frequency of 20 Hz. V o2 = mv pk-pk (Recall Value 3) Adjust the sine wave generator for 50 Hz, and if necessary, readjust the input signal (V i1 ) for 100 mv pk-pk. Measure V o2 at a frequency of 50 Hz. V o2 = mv pk-pk (Recall Value 4) Adjust the sine wave generator for 50 khz, and if necessary, readjust V i1 for 100 mv pk-pk. Measure V o2 at a frequency of 50 khz. V o2 = mv pk-pk (Recall Value 5) Adjust the sine wave generator for 100 khz, and if necessary, readjust V i1 for 100 mv pk-pk. Measure V o2 at a frequency of 100 khz. V o2 = mv pk-pk (Recall Value 6) FACET by Lab-Volt 229
RC Coupling Calculate the overall loaded circuit gain (Avc L ) with a 100 mv pk-pk input signal at a frequency of 20 Hz. Avc L = V o2 i1 = (Recall Value 7) 20 Hz mv pk-pk (Step 6, Recall Value 3) 50 Hz mv pk-pk (Step 7, Recall Value 4) 1 khz mv pk-pk (Step 5, Recall Value 2) 50 khz mv pk-pk (Step 8, Recall Value 5) 100 khz mv pk-pk (Step 9, Recall Value 6) Calculate Avc L with a 100 mv pk-pk input signal at a frequency of 50 Hz. Avc L = V o2 i1 = (Recall Value 8) Calculate Avc L with a 100 mv pk-pk input signal at a frequency of 1 khz. Avc L = V o2 i1 = (Recall Value 9) Calculate Avc L with a 100 mv pk-pk input signal at a frequency of 50 khz. Avc L = V o2 i1 = (Recall Value 10) Calculate Avc L with a 100 mv pk-pk input signal at a frequency of 100 khz. Avc L = V o2 i1 = (Recall Value 11) 230 FACET by Lab-Volt
gains (Avc (L) ). The X-axis of the frequency response curve is a logarithmic scale for the range of input signal frequencies of about 10 Hz to 1 MHz. FACET by Lab-Volt 231
RC Coupling Do the gains on the frequency curve increase sharply before a frequency of 20 Hz and decrease sharply after 100 khz? a. yes b. no Are the gains with frequencies in the audio frequency range of 20 Hz to 20 khz generally a. yes b. no The way in which gain varies with frequency is the frequency response. The bandwidth is the range of signal frequencies over which the gain is relatively constant. The size of the coupling capacitor affects frequency response at lower frequencies. and stray capacitance in the circuit elements. 232 FACET by Lab-Volt
1. The way in which gain varies with frequency is the a. bandwidth. b. frequency response. c. d. relative frequency. 2. a. bandwidth. b. frequency response. c. d. relative frequency. 3. The size of the coupling capacitor affects frequency response at which frequencies? a. high b. middle c. low d. all 4. a. resistor values are affected at high frequencies. b. the coupling capacitor starts to break down. c. of bias instability. d. 5. F to 5.0 F a. increases the bandwidth. b. decreases the bandwidth. c. does not affect the bandwidth. d. decreases the bandwidth at the higher frequencies. FACET by Lab-Volt 233