A 60 GHz Broadband LNA With Joined Variable Gain Control and Switching in 22 nm FD-SOI

Abstract

This paper investigates a 60 GHz low-power broadband low noise amplifier (LNA) with variable gain control. To prove the concept, the circuit is implemented in a 22nm fully depleted silicon on insulator (FD-SOI) CMOS technology. It supports broadband operation at 60 GHz achieved by gain peaking (gain distribution) technique. By tuning some key matching networks of the amplifier, the peak gain of each stage was distributed to different frequencies resulting in an overall broadband frequency response. The circuit consists of three cascaded cascode amplifier stages. Matching networks were optimized regarding bandwidth and noise figure. The transistor back-gate was used for LNA designs to switch the circuit to low-power standby mode. This avoids the problems of front-gate based switching regarding voltage breakdown and circuit stability. Additionally, simultaneous realization of variable gain control at such high frequencies was achieved via the back-gate. Compared to the front-gate based, the back-gate based variable gain control can deliver a continuous fine-tuning of the gain while requiring less accuracy or resolution of the control voltage. In the measurement, The gain was successfully tuned from 20dB down to -25dB via the back-gate. At a DC power of 8.1mW from a nominal supply of 1V, the LNA provides a peak gain of 20dB, a bandwidth of 18.5 GHz, and a minimum noise figure of 3.3dB. When biased at a reduced DC supply of 0.4V, the presented circuit consumes only 2.5mW of DC power, and still provides a power gain of 10dB and a minimum noise figure of around 4.5dB. By switching to standby mode, the LNA consumes 850 $\mathrm {\mu W }$ of DC power at the nominal supply and 240 $\mathrm {\mu W }$ at the reduced supply. The LNA compares well against previously reported designs by showing the lowest noise figure with competitive gain, bandwidth and DC power. To the authors’ knowledge, this is the first 60 GHz LNA featuring joined variable gain control and switching capability via solely back-gate biasing.

Keywords

• 22 nm FD-SOI
• 60 GHz
• broadband
• CMOS
• cascode circuit
• gain peaking technique