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Decibel Measurements
19 questions By Tony R. Kuphaldt
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Question 16 of 19
Calculate the overall voltage gain of this cascaded amplifier circuit, where the output of one voltage amplifier feeds into the input of another:
Also, convert the voltage gains of each amplifier into units of decibels, then convert the overall voltage gain ratio into units of decibels as well.
What do you notice about the overall gain of this circuit in relation to the individual amplifier gains, compared as ratios versus compared as decibel figures?
Reveal answerCascaded voltage gains expressed as ratios:
AV = 12 ×1 = 12 Cascaded voltage gains expressed a decibel figures:
AV = 21.58 dB 0 dB = 21.58 dB Notes:Besides providing practice with ratio-to-decibel conversions, the purpose of this question is for students to realize that gains multiply as ratios but add as decibels.
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Question 17 of 19
In this cascaded voltage divider circuit, determine the overall voltage gain ratio (from first input to last output), and also calculate the overall voltage gain in decibels, as well as the decibel figure for each divider’s voltage gain:
What do you notice about the ratio figures versus the decibel figures, regarding how the individual stage gains compare with the overall gain?
Reveal answer
Notes:Discuss with your students the nature of cascaded gain figures in both ratio and decibel formats. Which format is easier to calculate manually (without using a calculator)? Why is this?
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Question 18 of 19
In this circuit, one amplifier feeds into an attenuator circuit, which then feeds into a second amplifier stage. Calculate the “gain” of the attenuator, and then calculate the overall voltage gain of this three-stage circuit:
Also, convert the voltage gains of each stage into units of decibels, then convert the overall voltage gain ratio into units of decibels as well.
What do you notice about the overall gain of this circuit in relation to the individual amplifier gains, compared as ratios versus compared as decibel figures?
Reveal answerCascaded voltage gains expressed as ratios:
AV = 5 × ( 1 2) ×4 = 10 Cascaded voltage gains expressed a decibel figures:
AV = 13.98 dB (−6.02 dB) 12.04 = 20 dB Notes:Besides providing practice with ratio-to-decibel conversions, the purpose of this question is for students to realize that gains multiply as ratios but add as decibels.
