| 摘要 |
PROBLEM TO BE SOLVED: To provide a decoupling means to protect a sensitive receiver and coils from a transmitted RF signal. SOLUTION: Receiving coils D1 and D2 include a first decoupling circuit 28 disposed around the coils D1 and D2. During a transmitting part of a cycle, the decoupling circuit 28 detects a large-power RF pulse, and decouples the coil D 1 and D2. A high speed switching diode or PIN diode is energized by the transmitted RF pulse for changing an inductor 40 into the coils D1 and D2 to be connected for decoupling the coils D1 and D2. In a receiving part of the cycle in which the coils D1 and D2 are not used, a DC bias is selectively added to the coils D1 and D2 to put the diode on, so the coils D1 and D2 are positively decoupled. The DC bias also biases diode switches 50 and 50' for short-circuitting inputs of preamplifier elements 48 and 48' for protection.
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