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This paper presents a First Order Noise Shaping Local-Oscillator Based Time-to-Digital Converter (LO TDC). The architecture and governing equations of the LO TDC are described. In order to show the effect of noise shaping on the resolution of the TDC, the system “LO TDC plus moving average filter” is introduced. An equation to predict the resolution of the system “LO TDC plus filter” is given. Then, the Matlab model of the system “LO TDC plus filter” is illustrated briefly, and some example of simulated input-output characteristics are shown. Afterwards, the implementation of the LO TDC on an FPGA is described. A comparison between the predicted, simulated and measured values of the resolution of the system “LO TDC plus filter” is reported. Finally, we show spectra of the output signals of the LO TDC from experiments and simulations.