Triax transmitter and receiver interfaces and transmission system
View Patent ↗A triax transmitter interface for transmitting a video signal on a triax cable comprises a video signal input port, a first modulator for modulating a luminance component of a video signal received at said input port onto a first carrier and a second modulator for modulating a chrominance component of the video signal onto a second carrier, and a triax output port for outputting said modulated carriers to a triax cable. The first modulator is a quadrature modulator adapted to modulate luminance components of two video image lines simultaneously and in quadrature onto said first carrier. A receiver interface has a quadrature demodulator for restoring the luminance component.
1. A triax transmitter interface for selectively transmitting video signals having a first or a second field or frame rate on a triax cable, the first field or frame rate being lower than the second field or frame rate, comprising:
a video signal input port,
a first modulator for modulating a luminance component of a video signal received at said input port onto a first carrier,
a second modulator for modulating a chrominance component of the video signal onto a second carrier, and
a triax output port for outputting said modulated carriers to a triax cable;
wherein said first modulator is a quadrature modulator adapted to modulate luminance components of two video image lines simultaneously and in quadrature onto said first carrier,
wherein a first and a second memory are provided upstream of I and Q inputs of the first modulator, respectively, for buffering at least one of the two video image lines to be simultaneously modulated;
wherein, when video signals having the first field frame or frame rate are transmitted, the luminance component of each line is applied to a first input of the modulator without being delayed in the memory, a second input of the modulator not receiving a signal, and
wherein, when video signals having the second field or frame rate are transmitted each of the first and second memory receives at least one of the two video image lines to be modulated in quadrature, and outputs the respective video image line to the respective first and second input of the first modulator.
2. The triax transmitter interface according to claim 1 , wherein the data are read from the first and second memory at half the rate at which they are written into the memory.
3. The triax transmitter interface according to claim 1 , comprising means for transmitting phase synchronization signals for I and Q components of said modulated first carrier.
4. The triax transmitter interface according to claim 3 , wherein said phase synchronization signal transmitting means is adapted to transmit I component and Q component synchronization signals in a vertical blanking period of the video signal.
5. The triax transmitter interface according to claim 3 , wherein said synchronization signal is a white line.
6. The triax transmitter interface according to claim 3 , wherein said synchronization signal has a high frequency component.
7. The triax transmitter interface according to claim 6 , comprising a frequency divider for deriving the high frequency component from the first carrier.
8. The triax transmitter interface according to claim 1 , wherein, when video signals having the second field or frame rate are to be transmitted, signal processing means are connected between said video signal input port and said second modulator, which processing means are adapted to receive, in a given time unit, two lines of the chrominance component and to derive therefrom a single line to be supplied to the second modulator.
9. The triax transmitter of claim 1 , wherein, when video signals having the first frame rate are transmitted, the luminance component of each line is applied to the I input of the modulator without being delayed in the memory, the Q input of the modulator not receiving a signal, and wherein, when video signals having the second frame rate are transmitted, each of the first and the second memory receives at least one of the two video image lines to be modulated in quadrature, and outputs the respective video image line to the respective I and Q input of the first modulator.
10. The triax transmitter of claim 1 , wherein the second field or frame rate is twice the first field or frame rate.
11. A triax receiver interface for selectively receiving video signals having a first or a second field or frame rate generated by the transmitter interface according to claim 1 , comprising:
a triax input port for connecting to a triax cable,
a first demodulator for demodulating a luminance component of a video signal from a first carrier received at said input port, and
a second demodulator for demodulating a chrominance component of the video signal from a second carrier received at said input port,
wherein said first demodulator is a quadrature demodulator adapted to demodulate luminance components of two video image lines simultaneously and in quadrature from said first carrier, and
wherein a first and a second memory are provided downstream of I and Q outputs of the first demodulator, respectively, for buffering at least one of the two video image lines to be simultaneously demodulated
wherein, when video signals having the first field frame or frame rate are received, the luminance component of each line is output of the modulator without being delayed in the memory, a second output of the modulator not being used, and
wherein, when video signals having the second field or frame rate are received, each of the first and second memory receives at least one of the two demodulated video image lines from the respective first and second outputs of the first demodulator.
12. The triax receiver interface according to claim 11 , wherein the data are read from the memory first and second at twice the rate at which the data are written into the memory.
13. The triax receiver interface according to claim 11 , comprising means for detecting phase synchronization signals for I and Q components of said modulated first carrier in a signal received at said triax input port.
14. The triax receiver interface according to claim 11 , wherein an amplifier having a frequency dependent gain is connected between said triax input port and said first demodulator.
15. The triax receiver interface according to claim 14 , wherein a gain correction factor of said amplifier is controlled so as to minimize crosstalk between a high frequency component of a synchronization signal of one of said I and Q components and the other of said I and Q components obtained by the first demodulator.
16. The triax receiver interface of claim 11 , wherein, when video signals having the first frame rate are received, the luminance component of each line is output by the I output of the modulator without being delayed in the memory, the Q output of the modulator not providing a signal, and wherein, when video signals having the second frame rate are transmitted, each of the first and the second memory receives at least one of the two demodulated video image lines from the respective I and Q output of the first demodulator.
17. A triax transmission system for selectively transmitting and receiving video signals having a first or a second field or frame rate on a triax cable, the first field or frame rate being lower than the second field or frame rate, the system comprising a triax transmitter interface according to claim 1 .
18. The transmission system of claim 17 , wherein the transmitter interface and the receiver are connected by a triax cable, the system further comprising at least one all-pass filter having a group delay characteristic opposite to that of the triax cable.
19. A triax transmission system for selectively transmitting and receiving video signals having a first or a second field or frame rate on a triax cable, the first field or frame rate being lower than the second field or frame rate, the system comprising a triax receiver interface according to claim 11 .