Frequency-to-current converter

A frequency-to-current converter for accurately converting a clock frequency to an output current comprising:

• a digitally selectable capacitor having a capacitance value that is digitally selectable;
• a sampling capacitor operatively coupled via a first switch to the digitally selectable capacitor, the first switch operated by a first clock pulse from a clock generator responsive to a reference clock;
• an integrator circuit operatively coupled via a second switch to the sampling capacitor, the second switch operated by a second, non-overlapping clock pulse from the clock generator;
• a current mirror circuit operative for outputting a first current to the digitally selectable capacitor and for outputting a second current;
• and
• a transconductor operatively coupled to the integrator circuit and the current mirror circuit, the transconductor responsive to a comparison by the integrator circuit of a reference voltage and a voltage impressed on the sampling capacitor that is coupled to the integrator circuit by the second switch for conducting the second current from the current mirror circuit at a value related to the comparison,
• wherein in response to continuous operation of the non-overlapping first and second pulses, the value of the first current to the digitally selectable capacitor is controlled as a function of the value of the second current to cause the voltage impressed on the sampling capacitor to be made equal to the reference voltage, and the output current of the frequency-to-current converter is linearly proportional to a frequency of the reference clock and the capacitance value of the digitally selectable capacitor.