a The general structure of the prototype. It includes a buck/boost converter as a data transmitter and a receiver sharing a common power line with the buck/boost converter. vin denotes the input voltage of the buck converter. Data are transmitted from the buck/boost converter to the receiver via the dc power line. b Detailed circuit of the buck/boost converter, in which vin denotes the input voltage, Cin denotes the input capacitor while Cout denote the output capacitor. L denotes the inductor and Zload denotes the load. The modulated signal is the gate signal for MOSFET S1, and its complementary signal is the gate signal for MOSFET S2. c The structure of the receiver. It consists of load ZR, a signal conditioning circuit and a DSP with analogue-to-digital converter (ADC) to output digital data. d The signal conditioning circuit in the receiver. This circuit is composed of a dc blocking capacitor, a differential amplifier, an active second-order high-pass filter, an active second-order LPF and a dc voltage bias circuit. R1–R13 denote resistors, and C1–C5 denote capacitors. vripple denotes the conditioned signal voltage. The input signal, which has various frequency components and a large dc bias, is conditioned, and at the output port, a signal with a single frequency (a sinusoidal wave) and a proper dc bias is achieved.