## 1 Introduction  
Fourth-generation (4G) systems, such as time division duplexing (TDD) long-term evolution (TD-LTE), for mobile telecommunication have advanced highly. At present, the major TD-LTE frequency bands are 2.3 GHz (Band 40), 2.6 GHz (Band 41), and 3.5 GHz (Bands 42 and 43) [1]. To further boost the performance of LTE and provide faster and more secure mobile services, using LTE-unlicensed (LTE-U) band in the unlicensed 5-GHz spectrum with a cost-effective method is considered a favorable solution for achieving a larger bandwidth [2]. To further increase the traffic capacity, 5G communication technology has been proposed, and the Radio Spectrum Policy Group (RSPG) adopts the 3.6 GHz band for 5G communication in Europe [3, 4].  
IEEE 802.11 ac, with an operating frequency of 5 GHz, has been dubbed and specified as a Wi-Fi standard that is three times faster than IEEE 802.11n. Therefore, several coexistence schemes have been developed to allow efficient and fair spectrum sharing between LTE-U and WLAN [5, 6, 7]. WLAN standards [8] (IEEE 802.11a/b/g/n/ac) cover 2.4 and 5 GHz frequency bands, and different countries usually adopt different frequency bands for the limited bandwidth. Thus, highly integrated radio-frequency integrated circuits with multiple bands are becoming critical for use in TD-LTE, LTE-U, 5G, and WLAN applications. Moreover, owing to increasing demands of these new frequency bands in practical applications, compatibility with 2-, 3-, and 5-GHz bands operation has become challenging for low-noise amplifier (LNA) designers.  
Conventional design strategies for multiband communication have adopted different single-band transceiver circuits in parallel for achieving different frequency bands [9, 10];however, this has increased the implementation cost and current dissipation. To overcome the aforementioned drawbacks, topologies of wideband LNA have been designed and demonstrated for multiband applications [11; 12]. The broadband gain response causes undesired interference, thereby impairing the linearity of the receiver. A dual-resonant transformer-based matching network was analyzed and capable of two different frequencies [13], but a dual-band operation is insufficient to cover the latest triple-band wireless standard.  
Furthermore, a lossy silicon substrate lowers the quality factor of the spiral inductor, which limits the reliability of the LNA. Several papers have proposed methods for ameliorating the noise of LNAs. A flipped CMOS glass-integrated-passive-device (GIPD) package [14] and inductively coupled plasma (ICP) deep-trench technology [15] were utilized to improve the quality factor of off-chip and on-chip inductors. However, the extra processes of CMOS GIPD flip-chips and ICP created excessive costs of package and production.  
To achieve a wide range of wireless communication services, with up to 400, 400, and 800 MHz bandwidths from 2.3-2.7, 3.4-3.8, and 5.1-5.9 GHz bands, respectively, which include TD-LTE Band 40-41, Band 42-43, and the unlicensed 5-GHz band operation, with miniaturized circuit size, and less than 3 dB noise targeted for each band, we proposed a triple-band LNA that employs a switched narrow-band double-peak load matching mechanism to operate on triple-band and avoid unwanted interference, and decrease power consumption for multiband transceiver application. The input matching of the LNA is adopted by gyrator-based feedback topology to minimize the circuit size. Moreover, a noise cancellation technique with additional substrate resistor is presented to enhance noise figure performance.  
The rest of this paper is organized as follows. Section 2 introduces the design principle and analysis of the matching network and noise reduction technique used in this switched LNA. Section 3 details the triple-band LNA. The experimental results and conclusions are summarized in Sections 4 and 5, respectively.