2 Questions
Thursday, 12 July 2018
8:11 AM
Predict the resistance between terminals 1-2 and 2-3 for the potentiometer if the shaft is rotated fully CW.

Answer:



What is the difference between a potentiometer and a rheostat?

Answer:



Sketch of shifted sinusoid and AC component


Set the trigger on the DSO to use Channel 2 with HF Reject selected. HF Reject can be found under the Mode/Coupling key. 

On the FG, apply a “DC offset” of 3 V DC to the sinusoid.

Set the trigger on the DSO to use Channel 1 with HF Reject off.

Sketch the observed waveforms in the correct time relationship below. Show the voltages and time on your plot.

Sketch of square wave and AC-coupled square wave


Note: The AC input coupling capacitor has blocked the DC component of the waveform, allowing us to observe only the AC component.


Sketch of phase-shifted sinusoids



Note: AC coupling should be used with caution, because at low frequencies it can radically alter the observed waveform!


AC coupling will remove the DC component of a waveform

Set the FG frequency to around 3 Hz and measure the FG output on DSO Channels 1 and 2 simultaneously. Adjust the Horizontal Time/Div knob to display approximately 2 cycles of the sinusoid.

On the FG, turn the DC offset ‘off’. (Set to 0 V).
Change the FG to a 20 kHz sinusoid, and adjust the Horizontal Time/Div knob to display 2 cycles of the sinusoid.

Now reduce the amplitude of the sinusoid to 500 mVpp. Turn the Volts/Div knob on Channel 2 to 100 mV/div to display a fairly large sinusoid. We can now get “AC detail” from a waveform that has a large DC component:


Turn Channel 2 on by pressing the 2 key. Set 1 V/div on both channels. the Probe Attenuation Ratio is 1.00:1.

Change the FG to a square wave. Note the significant change in wave shape. Sketch the observed waveforms in the correct time relationship below. Show the voltages and time on your plot.

On the Channel 2 menu, set the Coupling to AC. You should see a “shifted” sinusoid on Channel 2. Sketch the observed waveforms in the correct time relationship below. Show the voltages and time on your plot.

The DSO has the ability to insert a capacitor between the external input and its internal analog acquisition circuitry. This can be represented by the circuit below, known as the input ‘coupling’ circuit:

Set Channel 2 to 1.00 V/div and then turn it off.

We will investigate the effect and use of the input coupling circuit.

Sketch of triangle wave and AC-coupled triangle wave

Change the FG to a triangle wave. Note the significant change in wave shape. Sketch the observed waveforms in the correct time relationship below. Show the voltages and time on your plot.

Table L2.1
Measure a 1 kΩ resistor for R1 and a 10 kΩ resistor for R2 . Record the measured value of resistance in Table L2.1.

Measured
Measured
Computed
A noninverting amplifier is illustrated in the figure below:
Measured
Measured
Measure the output voltage, v2. Record the measured value in Table L2.1.

Questions – Noninverting Amplifier

Calculate v2 using the computed closed-loop gain, and record the value in Table L2.1.

Connect the circuit shown in Figure L2.3 below. Note the polarity of the DC supply’s decoupling capacitors. 

R1
Set the function generator for a 500 mVpp sinusoidal wave at 1 kHz. The sinusoid should have no DC offset.

Figure L2.3 - Noninverting amplifier



Measured
Do not build the circuit in Figure L2.2

Continue down the page, follow the steps and build Figure L2.3
Measure the feedback voltage at pin 2 using Channel 2. Record the measured value in Table L2.1.
v(-)

500 mVpp

Av
In the Lab – Noninverting Amplifier
Noninverting amplifiers have an extremely high input resistance, and a very precise gain. The only disadvantage is that they can only produce a gain greater than or equal to 1.
Computed
R2
v1
Observe the input,  v1 on channel 1 of the DSO and v2 on channel 2.

In all subsequent parts of the lab, observe the input on channel 1 of the DSO and the output on channel 2. 
You may need to adjust the vertical attenuation settings on the DSO to obtain accurate readings.

Figure L2.2 - Noninverting amplifier
STOP: Ask a tutor to check your circuit before proceeding with the activity.
Explain the voltage measured at pin 2.

Answer: 



Using the measured resistances, compute the closed-loop gain of the noninverting amplifier. The closed-loop gain equation is given above.

The closed-loop voltage gain is:
v2
v2
Table L2.1
Express the measured gain of the amplifier in dB.

Answer: 



What is this amplifier called?

Answer: 



If R2 = 0 and R1 = ∞, what is the gain?

Answer: 



Explain the voltage measured at pin 2 of the TL071 IC.

Answer: 



This answer is a fundamental concept! Please have a discussion with a tutor if you don't understand.
8:11 AM
Thursday, 12 July 2018
Questions
Answer:



This answer is a fundamental concept! Please have a discussion with a tutor if you don't understand.
Explain the voltage measured at pin 2 of the TL071 IC.

What is this amplifier called?

Answer:


