Low distortion rf switching circuit without dc bias

Abstract

During a transmit cycle portion, a radio frequency transmitter (C) continuously generates an AC biasing signal and selectively generates a radio frequency signal. The AC biasing signal gates a first switch (10) and a second switch (32) such that the radio frequency signals from the transmitter are conducted to a magnetic resonance probe (E) but are blocked from being conducted to a receiver (F). A first filter (20) prevents the bias signals from being applied to the probe. The second switch includes a pair of crossed diodes (34, 36) which are gated conductive by the AC bias signal. A filter (72) passes the radio frequency signals but not the bias signals to ground to prevent the radio frequency signals from reaching the receiver. A filter (80) allows the bias signals to be applied across a load (88) such that the transmitter sees the load at the bias signal frequency. Another filter (40) prevents the bias signal from reaching the transmitter. An additional switch (50) provides further isolation between the receiver and the transmitter during the transmit cycle portion. During the receive cycle portion, radio frequency signals received by the probe pass through the filters (20,40) directly to the receiver but are blocked by switch (10) from passing to the transmitter.