An ultrasound sensor produces an output that needs to be amplified to 3.0 V - AQA - A-Level Physics - Question 2 - 2018 - Paper 8
Question 2
An ultrasound sensor produces an output that needs to be amplified to 3.0 V.
The amplifier used has a voltage gain of 40.
Calculate the input voltage $V_{in}$ to th... show full transcript
Worked Solution & Example Answer:An ultrasound sensor produces an output that needs to be amplified to 3.0 V - AQA - A-Level Physics - Question 2 - 2018 - Paper 8
Step 1
Calculate the input voltage $V_{in}$ to the amplifier from the sensor.
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Answer
To find the input voltage, we use the formula:
Vout=Vinimesextgain
Given that the output voltage Vout is 3.0 V and the gain is 40:
3.0=Vinimes40
Rearranging gives:
Vin=403.0=0.075 V
Step 2
Complete the circuit diagram in Figure 3 by adding and labelling two resistors, $R_{in}$ and $R_f$, so that the operational amplifier is correctly configured in its non-inverting mode.
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Answer
To configure the operational amplifier in non-inverting mode:
Connect Rin between the input signal and the non-inverting terminal (+).
Connect Rf between the output and the inverting terminal (-).
Ground the other end of Rf to ensure proper feedback.
Step 3
Determine, using resistors selected from the list below, how the voltage gain of 40 can be achieved by the non-inverting amplifier of Figure 3.
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Answer
The formula for the gain of a non-inverting amplifier is given by:
extgain=1+RinRf
Setting this equal to 40:
40=1+RinRf
This simplifies to:
39=RinRf
Choosing Rin=1kΩ gives:
Rf=39kΩ.
Step 4
Discuss whether this operational amplifier is suitable for amplifying the sensor’s output voltage.
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Answer
Given the ultrasound frequency of 50 kHz, we can calculate the required gain-bandwidth product:
gain×bandwidth=40×50 kHz=2.0 MHz
However, since the amplifier specification shows a maximum bandwidth of 1.0 MHz, this amplifier would not be suitable for this application, as it would not provide the necessary amplification without distorting the signal.
