Patent ID: 7250777

Claim:
A device for measuring a resistance, comprising: a comparator having an inverting input, a non-inverting input and an output, a flip-flop having a D input connected to the output of the comparator, a latch input for receiving a pulse signal at a fixed pulse repetition rate, and a Q output, the flip-flop being responsive to a pulse applied to the latch input to provide a signal level corresponding to the signal level at its D input to its Q output, a means for determining a proportion of time for which the Q output of the flip-flop is at the signal level corresponding to a first signal level at its D input, a reference voltage source connected to a first of the inputs of the comparator, and an integrator coupled between an output of the flip-flop and the second of the two inputs of the comparator, the integrator including a resistor whereby the integrator develops a voltage at the second input of the comparator that depends on said pulse repetition rate and on the resistance of said resistor, and wherein the comparator, the integrator and the flip-flop are connected in a negative feedback loop such that at steady state the voltage developed by the integrator at the second input of the comparator is substantially equal to the reference voltage.