Discussion
An 8-bit successive approximation analog to digital converter has full scale reading of 2.55 V and its conversion time for an analog input of 1 V is 20 µS. The conversion time for a 2 V input will be :
Answer: B
The conversion time is still 20 µS.
A successive approximation ADC tests one bit per clock cycle, starting from the most significant bit, so an n-bit conversion always takes n clock cycles, whatever the input voltage. An 8-bit converter that takes 20 µs for a 1 V input therefore also takes 20 µs for a 2 V input.
The options that halve or double the time assume the conversion time depends on the input level. That is true of a counting (ramp) ADC, whose counter must count up to the input, but not of a successive approximation ADC.
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