SCART interface design for European encrypted TV receivers

SCART is an interconnection interworking interface mandated by Europe to complete satellite television receivers, televisions, video recorders and other audio and video equipment. The standard SCART interface is a 21-pin connector that defines both audio and video signal transmission channels.

For DVRs (disc/hard disk recorders) exported to Europe, since they usually have the requirement to receive encrypted TV channels, an external encryption descrambling box must be connected during design, thus proposing the design of the SCART interface. New requirements. The schematic diagram of the entire system connection is shown in Figure 1. TVs, DVRs, and crypto descrambling boxes need to be interconnected via the SCART interface on a DVR (disc/hard disk recorder) and require the following functions:

(1) When a user watches a free channel program through a television, the channel can be simultaneously recorded by the DVR or a television program of other free channels.

(2) When the user watches the free channel program through the TV, the DVR can simultaneously record the programs of other premium channels (the pay TV channel signal is processed by the encryption descrambling box first).

figure 1

    The signal path to complete this function is: the TV receives the free channel program and plays it through its own tuner without switching with the SCART interface. At the same time, the DVR-TUNER signal is input to the SCART interface 2 through the two-selection switch, and output to the encrypted descrambling box, and then restored to a normal video signal through the encrypted descrambling box, and then transferred back to the input end of the DVR via the SCART interface 2 Complete the recording.

(3) The user watches the pay channel program through the TV (the pay TV channel signal is processed by the encryption descrambling box first), and the DVR can simultaneously record other free channels.

The signal path is: firstly connect the TV-TUNER signal to the SCART interface 1, and then enter the SCART interface 2 through the second selection switch and output it to the encrypted descrambling box, and then recover the normal video signal through the encrypted descrambling box, and then The SCART interface 2 is switched to the second selection switch, and finally connected to the SCART interface 1 to which the television is connected, and returned to the input end of the television. The DVR can then receive free channel programming and video recording through its own tuner without switching with the SCART interface.

figure 2

(4) The user watches the pay channel program through the TV (the pay TV channel signal is processed by the encryption descrambling box first), and the DVR can simultaneously record the pay channel (the pay TV channel signal is processed by the encryption descrambling box first). The signal path of this function is the encrypted signal path in the 2 and 3 modes.

(5) The user watches the program recorded by the DVR through the television. Under this function, the output signal of the DVR is first connected to the SCART interface 1 connected to the TV through a second selection switch, and finally connected to the input end of the TV.

Among the above five functions, except for the first function, which does not require the SCART interface to switch and connect directly in the TV and DVR (disc/HDD recorder), other functions need to design special audio and video that conforms to the SCART definition. Switch the circuit. The complexity of the entire SCART interface circuit is greatly increased by the addition of an encrypted descrambling box, so that the circuit can be more complicated if implemented with discrete analog switches.

The MAX4399 is Maxim's audio and video switch that provides three SCART interfaces. Its basic application is the satellite receiver SCART interface design. Figure 2 shows the internal block diagram of the MAX4399. Figure 3 shows a typical application circuit for the MAX4399. In a typical application circuit, an audio and video port of the MAX4399 is unidirectional and can be designed to be connected to the encoder output of a satellite receiver. The other three are bidirectional, standard audio and video SCART interfaces. Audio and video signals from all ports can be switched to any port for input/output within the MAX4399. A slight modification to this typical application circuit can form a perfect single-chip solution for the above applications.

image 3

    The TUNER inside the DVR (disc/HDD recorder) only outputs audio and video signals in one direction, and should be connected to the STB ENCODER one-way input port in Figure 3. The TV is connected to the TV SCART two-way audio and video input and output SCART port. The input and output of the DVR (disc/HDD recorder) are respectively connected to the VCR bidirectional audio and video input and output SCART port. The encryption descrambling box is connected to the auxiliary bidirectional audio and video input and output SCART port.

According to the MAX4399 internal switching matrix and switch design, we can see that each signal path needs to be realized. It can be seen that the implementation circuit of the above single-chip solution can completely solve the SCART interface design problem of the encrypted TV receiver.