Input impedance of low noise preamplifiers used for MRI with dual source FET, floating ground and permanent ground

摘要

A preamplifier (46) comprises a field effect transistor (64) in common source configuration. While the gate of the field effect transistor is coupled to an amplifier input circuit (e.g. MRI coil), the drain of the field effect transistor (64) is coupled to an amplifier output. The preamplifier comprises furthermore a first (66) and a second (68) source-ground connection. The first source-ground lead (66) couples the source of the field effect transistor to the ground node of the amplifier input circuit, while the second source-ground lead (68) couples the source of the field effect transistor to the ground node of the amplifier output circuit. As a result, amplifier output currents generate basically a voltage drop across the second source-ground lead (68). Thus, the amplifier input circuit is less influenced by any common voltage drop across any common source-ground connection.

主权项

1. A preamplifier device, comprising:
a field effect transistor (FET) device configured to receive a signal input to the preamplifier device, the FET device itself comprising: a single gate; a single drain; a first source of the FET device coupled to a floating ground; and a second source of the FET device coupled to a second ground.