Patent ID: 7511545

Claim:
An analog duty cycle replicating frequency converter for pulse width modulated signals comprising: an input for receiving an input signal having an electrical characteristic varying at a first frequency between a first pair of values with a variable duty cycle; a first time/voltage converter providing an output voltage representing a portion of a period of the input signal in which the electrical characteristic has a predetermined one of the two values; a first voltage responsive logarithmic current source coupled to receive the output voltage of the first time/voltage converter and provide a first current representing a logarithm of the portion of a period of the input signal in which the electrical characteristic has the predetermined one of the two values; a second time/voltage converter providing an output voltage representing the period of the input signal; a second voltage responsive logarithmic current source coupled to receive the output voltage of the second time/voltage converter and provide a second current representing a logarithm of the period of the input signal; a current difference responsive voltage source coupled to the first and second voltage responsive logarithmic current sources and adapted to generate an output voltage representing a difference between the first and second currents and thus a logarithm of the duty cycle of the input signal; an exponential voltage/current converter coupled to receive the output voltage of the current difference responsive voltage source and generate a third current exponentially derived therefrom and thus representing the duty cycle of the input signal; and an oscillator responsive to the third current to generate an output signal having an electrical characteristic varying at a second frequency between a second pair of values with the duty cycle of the input signal.