Abstract
This thesis explores the design and experimental demonstration of cryogenic amplifiers for measuring sensitive signals of high impedance devices in experimental low temperature condensed matter physics. It focuses on the use of off-the-shelf gallium arsenide (GaAs) pseudomorphic high-electron-mobility transistors (pHEMT) to create a high-bandwidth cryogenic transimpedance amplifier (TIA), aiming for fast and high resolution readout of quantum devices. Cryogenic TIAs were demonstrated to be promising option for real-time time-domain measurements, as well as for high resolution frequency domain measurement, when compared to previously implemented state-of-the-art cryogenic voltage amplifiers.
This thesis starts with a brief introduction of how types of electrical noise can affect the amplifier design. It is experimentally demonstrated that the low-frequency noise of the used pHEMTs is reduced when the transistors are cooled below 100 K. Common source voltage amplifier made using the same pHEMTs also experimentally show improvements in gain when cooled down to 77 K.
A cryogenic TIA with stabilizing lead-lag- and phase-lag compensators is designed and implemented. The amplifier is a three-stage design to get a low input impedance, which in turn reduces the parasitic low-pass filtering at the input when measuring high impedance devices installed inside of a cryogenic refrigerator. To obtain a low output impedance, an output buffer is implemented.
An analytical model of the amplifier is derived from the schematics and block diagram to analyze the stability and performance. The assembled amplifier was tested at 77 K and in 4 K, where it achieved a transimpedance of 105.3 dBΩ, or 184 kΩ, a bandwidth of 2.7 MHz, and an input-referred current noise of 1.0 × 10−26 A²/Hz.
These results demonstrate that the low-cost cryogenic TIA based on the off-the shelf GaAs pHEMTs is very promising alternative to the widely used cryogenic voltage amplifiers. In addition, they can significantly increase the measurement bandwidth of high impedance devices installed in the cryogenic refrigerator compared to conventional TIAs at room temperature.
This thesis starts with a brief introduction of how types of electrical noise can affect the amplifier design. It is experimentally demonstrated that the low-frequency noise of the used pHEMTs is reduced when the transistors are cooled below 100 K. Common source voltage amplifier made using the same pHEMTs also experimentally show improvements in gain when cooled down to 77 K.
A cryogenic TIA with stabilizing lead-lag- and phase-lag compensators is designed and implemented. The amplifier is a three-stage design to get a low input impedance, which in turn reduces the parasitic low-pass filtering at the input when measuring high impedance devices installed inside of a cryogenic refrigerator. To obtain a low output impedance, an output buffer is implemented.
An analytical model of the amplifier is derived from the schematics and block diagram to analyze the stability and performance. The assembled amplifier was tested at 77 K and in 4 K, where it achieved a transimpedance of 105.3 dBΩ, or 184 kΩ, a bandwidth of 2.7 MHz, and an input-referred current noise of 1.0 × 10−26 A²/Hz.
These results demonstrate that the low-cost cryogenic TIA based on the off-the shelf GaAs pHEMTs is very promising alternative to the widely used cryogenic voltage amplifiers. In addition, they can significantly increase the measurement bandwidth of high impedance devices installed in the cryogenic refrigerator compared to conventional TIAs at room temperature.
| Original language | English |
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| Qualification | Master Degree |
| Awarding Institution |
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| Supervisors/Advisors |
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| Award date | 27 May 2024 |
| Publisher | |
| Publication status | Published - 9 Apr 2024 |
| MoE publication type | G2 Master's thesis, polytechnic Master's thesis |
Keywords
- Cryogenic electronics
- Transimpedance amplifier
- Low-noise
- GaAs
- HEMT