Editing Analog-to-digital converter (section)

===Ramp-compare===
A ramp-compare ADC produces a [[Sawtooth wave|saw-tooth signal]] that ramps up or down then quickly returns to zero.<ref>Couch - 2001 - Digital and analog communication systems - Prentice Hall - New Jersey, USA</ref>
When the ramp starts, a timer starts counting. When the ramp voltage matches the input, a comparator fires, and the timer's value is recorded. Timed ramp converters can be implemented economically,{{efn|A very simple (nonlinear) ramp converter can be implemented with a microcontroller and one resistor and capacitor.<ref>{{cite web |url=http://www.atmel.com/dyn/resources/prod_documents/doc0942.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.atmel.com/dyn/resources/prod_documents/doc0942.pdf |archive-date=2022-10-09 |url-status=live |title=Atmel Application Note AVR400: Low Cost A/D Converter |website=atmel.com}}</ref>}}  however, the ramp time may be sensitive to temperature because the circuit generating the ramp is often a simple analog [[integrator]]. A more accurate converter uses a clocked counter driving a DAC. A special advantage of the ramp-compare system is that converting a second signal just requires another comparator and another register to store the timer value. To reduce sensitivity to input changes during conversion, a [[sample and hold]] can charge a capacitor with the instantaneous input voltage and the converter can time the time required to discharge with a [[constant current]].