This letter introduces time marker generator (TMG) using operational transconductance amplifier (OTA). It is composed of comparator (i.e. sine wave to square wave converter), integrator and clipper. The performance of the proposed circuit is examined using Cadence and the model parameters of a 180 nm technology process.  Later, the circuit was built with commercially available OTA (LM 13600), passive components used externally and tested at the outputs of comparator, integrator and clipper. Simulations and experimental results are shown that verify the proposed circuit of time marker generator.