Cryogenic High Linearity and Dynamic Range, C-Band Low Noise Amplifier for uMUX TES and CMB Readout Systems

We describe a two-stage cryogenic low noise amplifier (LNA) with a usable frequency range of 0.5 to 8 GHz (L to C-band) designed for operation at 4 Kelvin. The amplifier was designed to have high linearity and dynamic range with a low noise temperature and low power dissipation. The LNA uses two Diramics Indium Phosphide (InP) Pseudomorphic High Electron Mobility Transistors (pHEMTs) and other commercial surface mount (SMT) components. The use of SMT components minimizes the number of bond wires needed to assemble the amplifier increasing its manufacturability. The LNA has a gain of 25 dB with a gain flatness of ±1-2 dB and a power consumption at 4 Kelvin ranging from 3.4 to 8 mW. The measured noise temperature at an operating temperature of 10 Kelvin is less than 10 Kelvin from 1 GHz to 2 GHz, less than 8 Kelvin from 2 GHz to 4 GHz, less than 6 Kelvin from 4 GHz to 5 GHz and less than 4 Kelvin from 5 GHz to 9.5 GHz. The measured performance is in good agreement with the computer simulation with a output 1 dB compression point (OP1dB) ∼-5 dBm and input third order intercept point (IIP3) ∼ -12 dBm when measured with a full readout chain. The amplifier is designed to be used as the first stage LNA in the readout of arrays of microwave multiplexed transition edge sensors (TES) for the Simons Observatory¹ (SO) in Chile. A common problem with highly sensitive frequency multiplexed detectors is optimizing the probe-tone drive power without saturating the LNA. The high dynamic range of these LNAs sets a saturation point well above the saturation point of the detectors.