Voltage to frequency converter (VFC) is an oscillator whose frequency is linearly proportional to control voltage. The charge balanced VFC may be made in asynchronous or synchronous (clocked) forms. The synchronous charge balanced VFC or "sigma delta" (Σ-Δ) VFC (SVFC) is used when output pulses are synchronized to a clock. The charge balance VFC is more complex, more demanding in its supply voltage and current requirements, and more accurate. It is capable 16 to 18 bit linearity. The synchronous behaviour is good in many applications, but the output of SVFC is not a pure tone (plus harmonics) like a conventional VFC, but it contains components harmonically related to the clock frequency. In this paper, the new SVFC (NSVFC) is described. This NSVFC works similarly as conventional SVFC but it has a pure tone on output (for constant input voltage). Therefore, it is possible to measure the period of NSVFC output (this does not possible for SVFC).
Keywords:
A/D converters, voltage to frequency converter, sigma delta modulator
