Voltage source based voltage-to-time converter

Voltage-to-time converter (VTC) circuits are used as the core component of single-slope analog to digital converters (ADCs). These VTC circuits have traditionally depended on the use of a constant current source as part of their implementation in order to have good linearity. An alternative approach is presented where only voltage sources and a few discrete components are needed without sacrificing linearity. This circuit can be realized in hardware using general purpose IO (GPIO) pins that are available on all microcontrollers, FPGAs, and CPLDs. This provides more flexibility than current source based VTCs that rely on specialized hardware, allowing for a full ADC to be built using GPIO pins with no specialized ADC hardware.