Patent ID: 7349488

Claim:
A system for communicating between two integrated circuits, comprising: a first integrated circuit having a transmitter circuit for converting digital data into a frequency modulated signal, the first integrated circuit positioned on a first printed circuit board for transmission of the frequency modulated signal via a transmission line to a second integrated circuit; the frequency modulated signal representing the digital data as the frequency modulated signal includes signal components having frequencies representing logic states of the digital data; the second integrated circuit electrically coupled to the transmission line and having a receiver circuit for converting the frequency modulated signal back to the digital data, the second integrated circuit positioned on the first printed circuit board or on a second printed circuit board, wherein the second printed circuit board is connected to the first printed circuit board via a common backplane; the frequency modulated signal including an amplitude frequency shift keying (AFSK) signal the modulation circuit comprising; a frequency generator configured to generate a plurality of clock signals, each clock signal of the plurality of clock signals having a predetermined frequency; a modulation circuit configured to receive the digital data and at least one of the plurality of clock signals and configured to generate the AFSK signal; a first multiplexer configured to select a clock signal of the plurality of clock signals using a first bit of the digital data; an amplifier connected to the first multiplexer for amplifying the selected clock signal; and a second multiplexer connected to the amplifier and configured to select the selected clock signal, the second multiplexer controlled by a second bit of the digital data.