lesson
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Your microphone creates a smooth, continuous electrical voltage whenever you speak, but a computer processor can only understand discrete streams of binary ones and zeros. To bridge this gap, an analogue-to-digital converter (ADC) measures the analogue voltage and converts it into a digital binary number.
What is the simplest way to find an unknown voltage? Let's build a circuit that starts at zero and counts upward until it matches the input.
The Four Core Building Blocks
A digital ramp ADC (also called a staircase ADC) connects four fundamental electronic modules in a closed feedback loop: a square-wave clock generator, an N-bit binary counter, a digital-to-analogue converter (DAC), and an analogue voltage comparator.
πInteractive diagram
An analogue comparator is a high-gain differential amplifier that outputs a logic HIGH (1) whenever the analogue input voltage Vinβ at its non-inverting terminal exceeds the feedback voltage VDACβ at its inverting terminal, and switches to logic LOW (0) when VDACββ₯Vinβ.
Now that we see all four components wired together, how do they actually interact when a conversion begins?
The Sequential Operating Cycle
The sequential operating cycle begins when a reset/start pulse resets the counter to zero (00β¦02β), setting the DAC analogue output to VDACβ=0Β V.
The comparator then tests the analogue input against the DAC output (Vinβ>VDACβ), producing a logic HIGH that enables the AND gate to pass clock pulses to increment the counter.
πInteractive diagram
As the counter counts up, the DAC generates an escalating staircase/ramp voltage VDACβ.
When VDACββ₯Vinβ, the comparator output switches to logic LOW (End-of-Conversion, EOC). This LOW signal gates off the clock pulses, stopping the counter and triggering the output latch to capture the digital binary word corresponding to Vinβ.