Achieving Wideband sub-1dB Noise Figure and High Gain with MOSFETs if Input Power Matching is not Required

Abstract

-A 0.18 μm CMOS Low Noise Amplifier (LNA) achieves sub-1dB Noise Figure over more than an octave of bandwidth without external noise matching components. It is designed for a future radio telescope, requiring millions of cheap LNAs mounted directly on phased array antenna elements. The short distance between antenna and LNA and low frequency below 2GHz allows for using an LNA with reflective input impedance, increasing the gain with 6dB. Without any matching network, very low noise figure is achieved over a wide bandwidth. At 90mW power, sub-1dB Noise is achieved for 50Ω source impedance over a 0.8-1.8GHz band without external coils, and S21>20dB, OIP2>25dBm and OIP3>15dBm. Preliminary results with 150 Ω source impedance show noise temperatures as low as 25 K around 900 MHz.

Frequency Reconfiguration of a Dual-Band Phased Array Antenna With Variable-Impedance Matching

“…It this case, there is no reflected power wave ( ) and maximum power will be delivered to the antenna for radiation. It is worth pointing out here that the conventional travellingwave-based definition of reflection coefficient, (6) does not satisfy the above mentioned condition and fails to provide a physical meaning when the reference impedance is complex. In addition, as explained in [23] for (6) the magnitude of reflection coefficient can be larger than unity even for a passive system.…”

“…Historically, this impedance value was selected as a compromise between the minimum attenuation at around 77 Ω and the maximum power handling capability at around 30 Ω of an air-filled coaxial-line or waveguide [1]. However, having the liberty to choose another impedance value increases the design flexibility for both antennas and RF-frontends, and can enhance the total system performance dramatically [2][3][4][5][6][7]. Possibility to select reference impedances other than the 50 Ω value reveals the opportunity to use antenna structures for which the inherent input impedance is not 50 Ω [4].…”

“…Possibility to select reference impedances other than the 50 Ω value reveals the opportunity to use antenna structures for which the inherent input impedance is not 50 Ω [4]. In addition, [6][7] demonstrate improvements in gain and noise factor when the impedance of the RF-frontend is not obliged to match a single value.…”

Codesign of Electrically Short Antenna–Electronics Interfaces in the Receiving Mode

“…But since the equivalent Thévenin antenna voltage itself depends on the antenna resistance by V A = √ 8P av R A [6], the load voltage increases, although at a slower rate compared to Region I. On the other hand, Region II has a fundamentally wideband characteristic, which can be exploited in the design of wideband Low Noise Amplifiers (LNA), where relatively large antenna resistances of 150 Ω [7] have been reported in the literature.…”

“…In this case, a minimum R A should be selected during the optimization. The LNA input however, can be designed for maximum parallel resistance (i.e., purely capacitive input impedance) and therefore would increase the load voltage by 6 dB when keeping R A fixed at the minimum value [7]. It is important to point out that a conjugate matched interface in theory would increase the voltage even further, but in this case would require a purely inductive antenna with infinitely small antenna radiation resistance and conduction loss resistance, which of course is not realizable.…”