In a video phone for transmitting and receiving a video signal and a voice signal by means of a single transmission line, said video phone having a standard telephone having a hook switch, a displaying monitor and a self-camera, an apparatus for transmitting and receiving the voice signal simultaneously with the video signal via the single transmission line, said apparatus comprising:
- filtering means connected between said telephone and said transmission line, for inputting the voice signal from either said telephone or said transmission line and passing only voice signal with a frequency region below a first frequency set within a frequency band of said transmission line;
- video signal receiving means for discriminating if a carrier frequency in the video signal being sent via said transmission line from a counterpart is which of a second frequency or a third frequency set within said frequency band of said transmission line, demodulating the video signal by one of said second and third frequencies depending upon the discriminated result, and outputting the demodulated video signal to said displaying monitor;
- video signal transmitting means for inputting the video signal from said self-camera, modulating the video signal with the other of said second and third frequencies differently from said video signal receiving means and outputting the modulated video signal to said transmission line;
- interfacing means connected among said transmission line, said video signal receiving means and said video signal transmitting means, for separately outputting the video signals to be received and transmitted;
- a hook switch sensor for sensing ON/OFF states of said hook switch;
- a transmitting switch for outputting a control signal for transmission of the video signal;
- wherein said video signal transmitting means further comprises first video signal processing means for inputting the video signal from said self-camera and modulating and band-pass filtering the inputted video signal in response to an external control signal to send the modulated and band-pass filtered video signal to the counterpart;
- wherein said video signal receiving means further comprises second video signal processing means for inputting the video signal from the counterpart via said transmission line and modulating and band-pass filtering the inputted video signal in response to an external control signal to display the modulated and band-pass filtered video signal through said monitor;
- wherein said interfacing means further comprises an interface unit connected among said transmission line, said first video signal processing means and said second video signal processing means, for separately outputting the video signals to be received and transmitted;
- wherein said video signal receiving means further comprises a frequency discriminator for discriminating if the carrier frequency in the video signal from the counterpart is which of said second frequency or said third frequency set within said frequency band of said transmission line and outputting an acknowledge signal depending upon the discriminated result;
- a microprocessor for inputting output signals from said hook switch sensor, said transmitting switch and said frequency discriminator and outputting control signals to said first and second video signal processing means;
- said microprocessor adapted for perceiving by said output signals from said frequency discriminator and said transmitting switch that frequency component of the video signal sent from the counterpart was one of said second or third frequencies, designating the other of said second or third frequencies as the carrier frequency of the video signal for transmission in accordance with the perceived result, and outputting control signals according to the perceived and designated results to said first and second video signal processing means;
- and
- wherein said first video signal processing means further comprises:
- a timing signal generator for generating a clock signal,
- an A/D converter for inputting the video signal from said self-camera and digitizing the inputted video signal to be transmitted, in response to said clock signal from said timing signal generator,
- a memory controller for generating read/write select and address signals in response to the control signal from said microprocessor and said clock signal from said timing signal generator,
- a memory unit for storing the digitized video signal from said A/D converter in response to said read/write select and address signals from said memory controller,
- a carrier generator for generating said second frequency carrier or said third frequency carrier in response to the control signal from said microprocessor,
- a modulator for modulating the digitized video signal stored in said memory unitr146an output signal from said carrier generator,
- a first amplifier for amplifying an output signal from said modulator,
- a first band pass filter for passing only video signal with said second frequency component to said interface unit,
- a second band pass filter for passing only video signal with said third frequency component to said interface unit, and
- a first switching circuit for selectively outputting an output signal from said first amplifier to said first band pass filter or said second band pass filter in response to the control signal from said microprocessor.