An inquirer-side circuit of an automotive Ethernet system includes: a hybrid circuit arranged to operably couple with an MDI circuit to conduct data communication with a respondent-side circuit; a transmitting circuit coupled with a hybrid circuit and arranged to operably generate and provide a transmission signal to the hybrid circuit; a receiving circuit coupled with the hybrid circuit and arranged to operably receive and parse a received signal transmitted from the hybrid circuit to generate a data signal; a processing circuit coupled with the receiving circuit and arranged to operably process the data signal; a physical coding sublayer circuit coupled with the processing circuit and arranged to operably conduct a physical coding operation according to the instruction of the processing circuit to control the operations of the transmitting circuit; and an echo cancellation circuit coupled between the transmitting circuit and the receiving circuit.