A high-definition multimedia interface circuit uses a high-definition multimedia interface encoder to produce a plurality of channels of data. An output circuit, connected to the high-definition multimedia interface encoder, produces a plurality of channels of high frequency data from the data produced by the high-definition multimedia interface encoder. A multiplexer selects a channel for sampling, and a capacitive coupler capacitively couples the multiplexer to a sampling circuit. The sampling circuit produces sampled data corresponding to the high frequency data having a clock rate less than a clock rate of the high frequency data. A test circuit compares the sampled data with the data produced by the high-definition multimedia interface encoder.