# A 28-nm CMOS Low-Power/Low-Voltage 60-GHz LNA for High-Speed Communication
## 2 LNA Design  
The LNA stage is crucial for the overall RF receiver. Indeed, it must guarantee impedance matching to the antenna and deliver a sufficiently high signal to the demodula  
Figure 1: Typical structure of an mm-wave OOK transceiver for high-speed applications. tor, while producing the lowest possible degradation of the signal-to-noise ratio (SNR) at the constrained power budget. Therefore, the amplifier topology is of utmost importance to optimize RX performance. Compared to more widely used multistage topologies, compact LNAs are more effective due to better linearity, that is, the input 1 dB compression point (\(IP_{\rm 1 dB}\)), and a reduced risk of oscillations in the entire receiver. However, achieving both sufficiently high gain and a wide frequency bandwidth becomes more challenging when the number of amplification stages is low. On the other hand, most mm-wave CMOS LNAs employ the single-ended architecture due to their lower power consumption, reduced silicon area and simplified architecture, particularly when avoiding the need for single-ended-to-differential conversion at the mm-wave input. These factors make single-ended topologies attractive in scenarios where a minimal power budget and compact layout are the main constraints. However, single-ended structures are inherently more susceptible to common-mode noise injected from the supply voltage and/or substrate, especially at mm-wave frequencies, and offer no intrinsic path for ESD protection. Based on these considerations, the LNA depicted in Figure 2 has been designed. The differential input of the amplifier is connected to a 50-ohm single-ended antenna by means of the integrated input transformer, \(T_{\rm IN}\), which also provides impedance matching and ESD protection. The LNA adopts a pseudo-differential structure and consists of two amplification stages and an output buffer. Integrated transformers \(T_{\rm INT}/T_{\rm OUT}\) are extensively exploited as resonant loads, while enabling simple interstage connections and biasing. Despite the low supply voltage, \(V_{\rm DD}\), of 0.9 V, for the input stage of the LNA, the cascode (CAS) topology has been preferred to a more widely used common-source (CS) one. Indeed, the CS-based configuration exhibits better noise performance, but suffers from extremely poor input/output isolation, which involves the design of input/output matching networks, and can also lead to instability. On the other hand, both second and buffer stages adopt the CS topology to exploit all the available voltage headroom and maximize LNA linearity. It is worth noting that inductive degeneration (i.e., \(L_{\rm CNDI}\), \(L_{\rm CNDI2}\) and \(L_{\rm CNDI3}\)) models the parasitic path toward ground. As proposed in [11], power-efficient simultaneous noise impedance matching with source impedance transformation (_PE-SNIM_) is used for the first stage, given that conventional design methods for noise/impedance matching do not consider the constraints of the current budget in mm-wave CMOS LNAs. _PE-SNIM_ guarantees simultaneous noise and impedance matching at a low current level by means of inductive degeneration, \(L_{\rm CNDI}\), and proper sizing of the \(W/L\) ratio of the \(M_{\rm 1,2}\) pair. Specifically, an integrated transformer performs input impedance transformation, thus allowing each LNA branch  
Figure 2: Simplified schematic of the proposed stand-alone 60-GHz LNA. to be matched to \(2R_{\mathrm{S}}\) instead of \(R_{\mathrm{S}}/2\) by means of inductive degeneration, \(L_{\mathrm{GNDI}}\) (i.e., the parasitic path toward the ground plane). With a transistor bias current of only 2.6 mA, the first stage of the LNA achieves simultaneous noise/input matching thanks to the 1:4 input impedance step-up (i.e., from 50 \(\Omega\) to 200 \(\Omega\)) provided by the integrated transformer, \(T_{\mathrm{IN}}\). It is worth noting that the adoption of a traditional 1:1 input impedance ratio would require a differential stage with a current consumption about four times higher.