Preamplifier system with selectable input impedance

A preamplifier system comprising:

• an amplifier having an input operative to receive an input signal provided by an input signal system having an associated input impedance, the amplifier amplifies the input signal based on a gain factor associated with the amplifier to provide an output signal at an output of the amplifier;
• a plurality of selectable feedback paths coupleable between the output signal and the input signal, a selected feedback path comprising at least one of the plurality of selectable feedback paths to set an input impedance of the preamplifier system;
• and
• a selection mechanism that selects the selected feedback path to match the input impedance of the preamplifier system with the associated input impedance of the input signal system.
• wherein at least one of the plurality of selectable feedback paths comprises a transistor coupled to an output of the amplifier, an impedance matching resistor coupled to the transistor and the input of the amplifier, and a current source coupled to the resistor.

A differential preamplifier device comprising:

• a differential amplifier having a positive rail input terminal and a negative rail input terminal operative to receive a differential input signal provided by an input signal system over transmission lines, the input signal system and transmission lines having an associated input impedance including impedance due to a transmission line, the amplifier amplifies the differential input signal based on a gain factor associated with the amplifier to provide a differential output signal at a positive rail output terminal and a negative rail output terminal;
• a first set of selectable feedback paths coupleable between the positive rail output terminal and the negative rail input terminal;
• a second set of selectable feedback paths coupleable between the negative rail output terminal and the positive rail input terminal;
• and
• a selection mechanism that selects the selected feedback path to match the input impedance of the differential preamplifier with the associated input impedance including the impedance due to the transmission line of the input signal system and the transmission lines.

A differential preamplifier device comprising:

• a differential amplifier having a positive rail input terminal and a negative rail input terminal operative to receive a differential input signal provided by an input signal system over transmission lines, the input signal system and transmission lines having an associated input impedance, the amplifier amplifies the differential input signal based on a gain factor associated with the amplifier to provide a differential output signal at a positive rail output terminal and a negative rail output terminal;
• a first set of selectable feedback paths coupleable between the positive rail output terminal and the negative rail input terminal;
• a second set of selectable feedback paths coupleable between the negative rail output terminal and the positive rail input terminal;
• and
• a selection mechanism that selects the selected feedback path to match the input impedance of the differential preamplifier with the associated input impedance of the input signal system and the transmission lines,
• wherein the first set of selectable feedback paths comprising a first and a second feedback path that each employ a transistor coupled the positive rail output terminal, an impedance matching resistor coupled to the transistor and the negative rail input terminal of the amplifier, the impedance matching resistor being further coupled to a current source.