Flash (parallel) ADC operation – do flash converters require an external input clock pulse for each conversion, or do they resolve input levels combinationally with optional output latching?

Introduction / Context:
Flash ADCs are the fastest architecture for moderate resolutions, using many parallel comparators to encode the input level instantly. This question evaluates whether a flash ADC inherently depends on an input clock to perform a conversion.

Given Data / Assumptions:

• N-bit flash uses 2^N - 1 comparators and a resistor ladder.
• The thermometer code is encoded into binary.
• Designs may add latches/registers for timing alignment.

Concept / Approach:
A pure flash front-end resolves the input level as soon as the analog comparators settle—no explicit “start conversion” clock is required for the analog decision. However, practical converters often include clocked latches or pipelines at the outputs to synchronize data to a system clock. The conversion itself is combinational; the clock is used for capturing and transferring results, not for performing the analog comparison process.

Step-by-Step Solution:

Verification / Alternative check:
Datasheets describe “track-and-hold” and output register clocks but do not require a “start conversion” clock as in SAR or successive-approximation loops.

Why Other Options Are Wrong:
Claiming a conversion clock is mandatory confuses output synchronization with the analog decision mechanism. Nonoverlapping clocks or PLLs are unrelated to the basic flash principle.

Common Pitfalls:
Assuming all ADCs step through time-sequenced algorithms; flash is inherently parallel and instantaneous within analog settling limits.

Final Answer:
Incorrect