Editing Analog-to-digital converter (section)

===Intermediate FM stage===
An ADC with an intermediate FM stage first uses a [[voltage-to-frequency converter]] to produce an oscillating signal with a frequency proportional to the voltage of the input signal, and then uses a [[frequency counter]] to convert that frequency into a digital count proportional to the desired signal voltage. Longer integration times allow for higher resolutions. Likewise, the speed of the converter can be improved by sacrificing resolution. The two parts of the ADC may be widely separated, with the frequency signal passed through an [[opto-isolator]] or transmitted wirelessly. Some such ADCs use sine wave or square wave [[frequency modulation]]; others use [[pulse-frequency modulation]]. Such ADCs were once the most popular way to show a digital display of the status of a remote analog sensor.<ref>
[http://www.analog.com/static/imported-files/tutorials/MT-028.pdf Analog Devices MT-028 Tutorial: "Voltage-to-Frequency Converters"] by Walt Kester and James Bryant 2009,
apparently adapted from Kester, Walter Allan (2005) [https://books.google.com/books?id=0aeBS6SgtR4C&pg=RA2-PA274 ''Data conversion handbook''], Newnes, p. 274, {{ISBN|0750678410}}.</ref><ref>
[http://ww1.microchip.com/downloads/en/AppNotes/00795a.pdf Microchip AN795 "Voltage to Frequency / Frequency to Voltage Converter"] p. 4: "13-bit A/D converter"
</ref><ref>Carr, Joseph J. (1996) [https://books.google.com/books?id=1yBTAAAAMAAJ ''Elements of electronic instrumentation and measurement''], Prentice Hall, p. 402, {{ISBN|0133416860}}.</ref><ref>[http://www.globalspec.com/reference/3127/Voltage-to-Frequency-Analog-to-Digital-Converters "Voltage-to-Frequency Analog-to-Digital Converters"]. globalspec.com</ref><ref>Pease, Robert A. (1991) [https://books.google.com/books?id=3kY4-HYLqh0C&pg=PA130 ''Troubleshooting Analog Circuits''], Newnes, p. 130, {{ISBN|0750694998}}.</ref>