Amplitude-Shift-Keying Power Line Modem
Created: Sep 15, 2014
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The TDA5051A is a complete Amplitude Shift Keying (ASK) modem for transmitting and receiving digital signals on standard power line or any two-wire AC or DC network. It is a cost-effective solution that transmits at a rate of 600 baud (typical) and 1200 baud (maximum), operates from a single 5 V supply, and enables easy connection to standard microcontrollers. ASK is a form of amplitude modulation that represents digital data as variations in the amplitude of a carrier wave. In an ASK system, the binary symbol 1 is represented by transmitting a fixed-amplitude carrier wave and fixed frequency for a bit duration.
The use of a digital structure for both transmission and reception part provides an efficient solution for modulating and demodulating low baud rate data signals. A standard quartz crystal is required to set the operation frequency; in transmission mode, it defines the carrier frequency and in reception mode it defines the detection frequency. The coupling network is the interface between the power line and the low voltage TX_OUT and RX_IN pins of the modem. when the insulation with the mains is not required, a double LC network can be used, providing efficiency without any adjustment or tunable components. When an insulation is mandatory, an HF transformer should be used. The filter has two purposes; the reception mode that provides an efficient rejection of the 50Hz signal (high-pass) and anti-aliasing (low-pass) for the digital filter and the transmission mode that provides a rejection of unexpected harmonics in order to comply with the EN50065-1 standard.
In order to reduce the size of the components, a solution could be to use an R-C power supply in association with a switch mode converter. The R-C supply is used to reduce the mains voltage from 230 V AC to 28 V DC, for example, and then the switch mode converter provides the +5 V regulated output.