Test system and method for testing a circuit

1. A test-device for testing an electric circuit, comprising:

a data stream generator for generating a first data stream to be fed to an electric circuit which generates a second data stream in response to said first data stream;

a comparison-device which is configured to compare a first data stream and a second data stream and to generate a corresponding signal;

an output-device configured to output said signal;

a self-test device configured to generate a third data stream which is used to test said comparison-device; and

a gate which blocks feeding said first data stream to said comparison-device, if said first data stream matches said third data stream;

said test-device being configured to operate in a first operation mode and in a second operation mode, wherein said comparison-device compares said first data stream with said second data stream during said first operation mode and compares said first data stream with said third data stream during said second operation mode.

2. The test-device of claim 1 , comprising a switching-device configured to switch said test-device between said first operation mode and said second operation mode.

3. The test-device of claim 1 , wherein at least one of said first, second, and third data streams has a width of four bits.

4. The test-device of claim 1 , wherein said signal is output as a one-bit-wide erroneous signal or error-free signal.

5. The test-device of claim 1 , comprising a transmission-device configured to transmit said second data stream from said electric circuit to said comparison-device.

6. The test-device of claim 1 , wherein said data stream generator is configured to adapt said first data stream in accordance to said electric circuit.

7. A method for testing an electric circuit, comprising the steps of:

generating a first data stream with a data stream generator;

feeding the first data stream to an electric circuit which generates a second data stream in response to said first data stream;

comparing said first data stream with said second data stream using a comparison-device during a first operation mode;

obtaining a signal based on said comparison of said first data stream with said second data stream;

outputting said signal using an output-device;

generating a third data stream using a self-test device during a second operation mode;

comparing said first data stream with said third data stream using said comparison-device;

checking if said first data stream matches said third data stream;

blocking feeding said first data stream if said first data stream matches said third data stream using a gate;

determining if the comparison-device is functional during said second operation mode due to said comparison of said first data stream with said third data stream; and

outputting said signal using said output-device only, if it is determined that said comparison-device is functional during said second operation mode.

8. The method of claim 7 , comprising switching between said first operation mode and said second operation mode using a switching-device.

9. The method of claim 7 , wherein said signal is output as a one-bit-wide erroneous signal or error-free signal.

10. The method of claim 7 , comprising transmitting said second data stream from said electric circuit to said comparison-device by means of a transmission-device.

11. The method of claim 7 , comprising adapting said first data stream to said electric circuit.

12. The method of claim 7 , comprising determining if said comparison-device is functional during said second operation mode using different data rates.