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A Johnson decade counter uses a Johnson counter together with decoding logic - AQA - A-Level Physics - Question 4 - 2021 - Paper 8
Question 4
A Johnson decade counter uses a Johnson counter together with decoding logic. This arrangement produces a single logic 1 at a series of outputs Q0–Q9 in a continuous... show full transcript
Worked Solution & Example Answer:A Johnson decade counter uses a Johnson counter together with decoding logic - AQA - A-Level Physics - Question 4 - 2021 - Paper 8
Step 1
Describe one functional difference and one functional similarity between how a Johnson decade counter and a BCD counter output their counts.
Answer
Functional Difference: A Johnson decade counter outputs a sequence of binary codes, resulting in only one output being high at a time, whereas a BCD counter outputs multiple bits representing a binary number continuously in a 4-bit format.
Functional Similarity: Both counters recycle their outputs to represent the count up to 10, with both resetting when reaching their maximum count of 9.
Step 2
Determine the duty cycle and frequency of the signal.
Answer
Duty Cycle: From the oscilloscope, the time high = 5 div x 50 μs/div = 250 μs The time low = 3 div x 50 μs/div = 150 μs Thus, total period = 250 μs + 150 μs = 400 μs
Duty Cycle = (Time High / Total Period) x 100% = (250 μs / 400 μs) x 100% = 62.5%.
Frequency: Using the frequency formula, f = 1/T, where T = Total Period is 400 μs, f = 1 / (400 x 10^-6) = 2.5 kHz.
Step 3