XScopes
User’s Manual
DS-XScopes-3.5
– December, 2014
Page | 37
8.4
BJT Amplifier
1)
Build the circuit shown on figure 69.
2)
Set the time base to 2ms/div
3)
Move the position on both channels all the way down
(GND reference grid is at the bottom of the screen).
4)
Set CH1 to 0.32V/div, Set CH2 to 1.28V/div.
5)
Set the AWG to Sine wave, 125Hz, 0.250V amplitude.
6)
Increase the AWG offset until the CH2 wave is centered on the display. The display should look like figure 68.
Theory of operation: The transistor needs to be biased in its forward active region; this is what the offset in the AWG is for.
The output voltage will vary according to the BJT transfer curve: changes in the input make large changes in the output.
8.5
Component V/I Curves
1)
Build the circuit shown in figure 72, or flip the CURVE switch on the Portables.
2)
On the Portables, flip the input switches to the DC position.
3)
Set the time base to 500µs/div.
4)
Set the AWG to Sine wave, 125Hz, 4V.
5)
Set the gain on both channels to:
0.64V/div, or 1.28V/div on the Portables.
6)
Enter the CH2 options and select SUBTRACT.
7)
Set the device oscilloscope in XY mode.
Theory of operation: The goal is to plot the component’s voltage, versus the component’s current. Using the integrated
waveform generator and a 1kΩ resistor, we can inject current into the component. The voltage is measured directly using
CH1. The current thru the component is the same as the current thru the resistor, the voltage on the resistor is
proportional to the current. The voltage on the resistor is equal to CH2-CH1. 1V on the scope will represent 1mA on the
component. Figure 70 and figure 77 show examples of V/I curves on components.
8.6
Frequency Plots
The AWG sweep function can be used to plot the frequency response of a circuit. This method is not directly a BODE
plot since the horizontal axis is not logarithmic, it is linear.
1)
Connect the AWG to the input and CH1 to the output.
2)
Set the device to FFT mode.
3)
Change to the desired time base. The maximum
frequency is shown on the top right of the display.
4)
Set the AWG to Sine Wave.
5)
Enable the Frequency Sweep.
6)
Set the AWG Sweep range to 1:255
7)
Set the display to persistent.
Figure 73 shows an RLC circuit, and figure 74 shows the frequency response.
This example shows the vertical scale with the LOG disabled.
Figure 72: Component tester
Figure 71: 1N4148 curve
Figure 70: 100nF Capacitor curve
Figure 69: Amplifier circuit
Figure 68: BJT Measurements
Figure 73: RLC Circuit
Figure 74: Frequency plot
Summary of Contents for XScopes
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