Impedance measuring instrument

A measurement instrument for measuring the impedance of a device under test (DUT), said instrument comprising:

• a first source of either a voltage or a current;
• and
• a second source of either a voltage or a current, wherein the first source is connectable in a first feedback relationship with said DUT and said second source is connectable in a second feedback relationship with said DUT, said first feedback relationship being contained within said second feedback relationship, said first and second sources being operated respectively as a current source responsive to the current through the DUT and a voltage source responsive to the voltage across the DUT or operated respectively as a voltage source responsive to the voltage across the DUT and a current source responsive to the current through the DUT, said second feedback relationship having a narrower loop bandwidth than said first feedback relationship, the resulting voltage across the DUT and the current through the DUT establishing the measured impedance of the DUT.