Traveling wave amplifiers (TWAs) offer the advantage of broadband amplification and a closed set of equations that allow deriving the RF gain by means of treating TWAs as discrete transmission line approximations. Up to now, however, the significant losses associated with CMOS integrated inductors have been neglected. This work presents a new approach for determining the transmission line losses and phase constants that will bring about an enhanced gain prediction accuracy. The theory is verified by means of a realized design example. The working principle of the integrated DC supply inductor is discussed, whose performance is based on the inductors self-resonance effect. When applying a supply voltage V dd of 2.4 V, the measured compression point P 1dB and the power added efficiency PAE at 2.4 GHz amount to 16.9 dBm and 19.6%, respectively. At 5.5 GHz, a value of 16.6 dBm for P 1dB and an associated PAE of 13.9% are achieved. The peak RF gain for these output power values reaches 11 dB, and values greater than 8 dB are obtained up to 7 GHz.
I . I N T R O D U C T I O NA trend that is developing in recent years is the requirement for mobile RF frontends to accommodate several RF transmission standards. From a power amplifier (PA) perspective, multi-standard signal transmission at frequencies of 2.4 GHz (802.15.1) up to 5.725 GHz (802.11.x) requires broadband amplifiers such as e.g. traveling wave amplifiers (TWAs). The TWA principle, first introduced by Percival [1] and Ginzton et al. [2], was at the beginning envisaged for circuit realizations by means of vacuum tubes, discrete inductors, and capacitors. Ayasli et al. [3] and Beyer et al. [4] developed the original equations set further for the accommodation of the structural conditions that arise when implementing TWAs in GaAs FET technology. With the high substrate resistance of GaAs, the parasitic losses associated with the inductors could be neglected and the dominant loss factor reducing the RF gain versus frequency was the input gate source resistance R gs . Given this background, the developed equation sets were satisfactorily adequate to predict the achievable gain bandwidth product (GBW) of TWAs.With the rise of CMOS integration as the major circuit technology nowadays, this, unfortunately, is no longer the case. Parasitic series and parallel losses associated with the integrated inductors significantly influence the overall circuit behavior. This is particularly true for TWA architectures, which heavily rely on integrated inductors to approximate the input and output transmission lines.In this work, we propose a practical analytical solution for TWA architectures that incorporates the dominant loss factors of CMOS integrated inductors. A discrete transmission line model is presented that comprises resistive, capacitive, and inductive effects occurring in CMOS TWA realizations. Based on this model, the associated transmission line damping factor and phase constant are calculated and used for the derivation of the small signal gain. The RF gain is the...