The amplifier, once integrated and packaged into a single device, has the potential for use in monitoring and closed-loop control circuitry applications within a variety of harsh environment industries; such as aerospace, oil and gas, geothermal energy and nuclear.
“For this project we’ve focussed on creating circuitry that can operate in high temperature and other harsh environments,” explained Dr Alton Horsfall, reader in Semiconductor Technology at Newcastle University. “This could therefore lead to condition monitoring circuitry mounted on gas turbines or within the primary coolant loop of a nuclear reactor, which runs at about 350°C.”
The amplifier circuit features a lateral small-signal Junction Field Effect Transistor (JFET) that is said to offer improved reliability in hostile environments because of the lack of a gate oxide layer. According to the researchers, this is claimed to result in greater stability in the threshold voltage and reduction in the intrinsic noise, suiting these structures to the creation of high temperature, low noise amplifier circuits.
The current circuit is a fully differential, three stage amplifier, with a source follower final stage, optimised to operate on a ±15V supply. Modifications enable voltage supplies of ±45V to be utilised to increase the voltage headroom of the circuit.
Laboratory tests have shown the amplifier circuit has an open circuit gain in excess of 1500 at room temperature. A high temperature gain of 200 has been recorded at 400°C, but this is said to be limited by the passive components used in the circuit.
Phil Burnside, business development manager of Raytheon UK’s Semiconductors Business Unit, said: “We believe this amplifier circuit represents the furthest anyone has gone down the lab-to-fab route. In this instance, it is Newcastle University’s design expertise and understanding of harsh environments, combined with our Silicon Carbide processing expertise, that have the potential to result in the full commercialisation of a high temperature version of a fundamental electronic building block, the humble Op Amp.”
