Design of Wideband Power Amplifier in 130nm CMOS for LTE Applications

— Multiband power amplifier (PA) has become a crucial requirement for mobile communication systems that operate in variety bandwidth ranges along with different frequencies and output power. Replacement of more than two power amplifiers (PAs) by a single wideband PA is required to minimize power consumption and the chip size. This paper proposes, a wideband PA withfiltered matching network (FMN) to provide a wider bandwidth while improving linearity by harmonic suppression. The proposed matching network offers an operating bandwidth of 1.47GHz from the frequency 900MHz towards 2370MHz, covering 24 LTE frequency bands. The frequency range is achieved at maximum output power of 27.5dBm with linear power of 26dBm at 1-dB point. The ACLR value of -34dBc is achieved at 1-dB output power which is within the requirement of LTE linearity specification.

matching network that is designed to operate on wide continuous range of frequencies between 900MHz to 2370MHz. The focus of this research is to design a wideband PA operating in frequencies from 900MHz to 2370MHz.These specifications comply with 3GPP standards of operating LTE/LTE-A throughout the world. In this research, the proposed filtered matching network (FMN) aimed to improve the key parameters of the PA which are bandwidth and the output power. The input and output matching networks along with the PA design is analysed for achievement of wide bandwidth and linear output power. Furthermore, the power amplifier linearity performance is evaluated in terms of ACLR. Then an improving bandwidth and output power amplifier would be achieved by optimizing the matching network. A maximized efficiency at extended linear region of power amplifier is allowed by using matching network.

II. METHODOLOGY
Mobile communication systems operating over a frequency range of 700MHz to 3500MHz are standardized for 2G and beyond LTE/LTE-A. Figure 1 shows the proposed matching network along with PA architecture. The input matching network, is a combination of cascaded LC that is also indicated in Figure 2. The LC network provides an optimized impedance transformation through harmonic suppression of power amplifier's signal. On the contrary, the output matching network is designed using T-section band pass filter architecture which ensures further harmonic suppression and impedance transformation of PA signal. Distortions caused by harmonics are reduced at the input and output matching network by use of filter which shows that harmonic suppression is highly required.
The proposed filtered matching network (FMN) in the PA design is shown in Figure 2. The designed PA allows VDD supply of 3.3V to the transistors without exceeding the potential breakdown of transistor's oxide. The transistors are divided into four cells to reduce the parasitic effect and its outputs are combined by means of T-section filters. This architecture results improved ACLR performance as it eliminates the harmonics caused by the PA. Therefore, proposed FMN will provide good matching and improves all the PA parameters such as bandwidth, output power, gain, and ACLR.

A. Design Principles
The input matching network that includes LC impedance transformation stage is designed for a source impedance, Zs = 50Ω, with measured PA input impedance, Z in,PA of 2.6-j7Ω using cadence simulation. The input matching network's capacitive and inductive parameters is determined using equations (1) to (5) [33]: Where R in of 50Ω and f c of 2370 MHz from equations (1) and (2) are known as input resistance and carrier frequency. From equations (1) and (2), it can be determined that The design equation for capacitance (C 1 ) and inductance (L 1 ) for the LC matching network at input side are expressed as in equation (4) and (5): Where equation (4) also applies to the calculation for C 2 , C 3 and C 4. Similarly, equation (5) applies to L 2 , L 3 and L 4.
Similarly, the output matching network is designed for load impedance, Z L = 50Ω, and the measured PA output impedance, Z out,PA as2.2-j0.8Ω. The output matching network aspects is derived through equations (6) to (11) [33]:  ncy. Also, ensure that h.

III. RESULTS
The S-parameter analysis has been conducted to determine the bandwidth performance of the designed PA using cadence simulation and the results are indicated in Figure 4.  Figure 4. Gain represented by S21 shows value of 20.63dB as indicated in the S-parameter. The S11 and S22 are reflection coefficients which are below 0dB indicating that performance throughout the bandwidth is optimized by matching network.
The periodic steady state analysis implies the performance of output power of the PA is shown in Figure 5.It is clearly evident from the results that the peak output power is 27.5dBm and the linear output power of 26dBm at 1-dB compression point. In addition, the results produced by the designed PA clearly complies with LTE specification with output power requirement of 23dBm [5]. Similarly, Figure 6 indicates that an ACLR -34dBc has been achieved for the PA output power of 27.5dBm which is 1dBc better than the ACLR requirement of LTE which is -33dBc as shown in ACLR analysis of PA design [5]. Table I  IV. CONCLUSION In this paper, a wideband PA with filtered matching network (FMN) is proposed, designed and simulated at LTE bands. The results obtained clearly indicate that the PA provides an appreciable gain of 20.63 dB over the frequency ranging from 900 to 2370MHz and has an output power of 27.5dBm with reduced ACLR of -34dBc. The proposed wideband PA with filtered matching network operates over 24 LTE bands stated in section III. The proposed PA is a feasible solution for the current demand ofwideband PA in mobile communication systems.