Test board

A test board, serving as an interface for testing a conference phone, comprising:

• a plurality of test channel selecting modules, each comprising:
• a plurality of first test channel selectors, each of the first test channel selectors receiving a plurality of test voltages transmitted by the conference phone and a first, a second and a third control signals, the test voltages being grouped into a plurality of test voltage pairs and each of the test voltage pairs comprising two of the test voltages, and each of the first test channel selectors directly selecting one of the test voltages in each of the test voltage pairs according to the first control signal for generating a plurality of first selected voltages, and selecting four of the first selected voltages according to the second control signal for generating a plurality of second selected voltages, and selecting two of the second selected voltages according to the third control signal for generating a plurality of third selected voltages;
• and
• a second test channel selector, coupled to the first test channel selectors, and receiving the third selected voltages, and a fourth and a fifth control signals, wherein the third selected voltages are divided into a plurality of test voltage pairs, and each of the second test channel selectors selects one of the test voltages in each of the test voltage pairs according to the fourth control signal for generating a plurality of fourth selected voltages, and selects two of the fourth selected voltages according to the fourth control signal for generating a first and a second output voltages,
• wherein each of the first test channel selectors comprises:
• a plurality of first selection switches, each having a first to fourth input ends, a first to second output ends and a control end, wherein the control end receives the first control signal, the first and second input ends receive one of the test voltage pairs, and the third and the fourth input end receive the other one of the test voltage pairs, the first output end transmits a voltage on the first input end or the second input end, and the second output end transmits a voltage on the third input end or the fourth input end, wherein the first and the second output ends of the first selection switches generate the first selected voltages;
• a plurality of second selection switches, each having a first to fourth input ends, a first to second output ends and a control end, wherein the control end receives the second control signal, the first and second input ends receive two of the first selected voltages, and the third and the fourth input end receive the other two of the first selected voltages, the first output end transmits a voltage on the first input end or the second input end, and the second output end transmits a voltage on the third input end or the fourth input end, wherein the first and the second output ends of the second selection switches generate the second selected voltages;
• and
• a third selection switch, selecting two of the second selected voltages as the third selected voltages according to the third control signal.