Study, Modeling and Characterization of Dual-Band LNA Amplifiers Receivers for Wireless Microwaves Communication Systems

The new current design is especially suitable for use in multi-standard wireless receiver for microwaves communication systems. In recent years, there has been a growing market for dual band transceivers for various wireless standards. This work investigates a novel circuit topology of concurrent Dual-band Low Noise Amplifier (LNA) operates in the 3.9 GHz and 4.48 GHz frequency bands for WLAN applications and may be used for dual band cellular applications. RF circuit designs take two parallel LNAs with a single transistor only, and band-pass filter (BPF) networks are usually used match both the input and output ports at two different bands, are matched to 50Ω without external elements. The transistor ATF1 0136 is chosen for the purpose of high gain and low noise characteristics. Simulations of the operation of the amplifier were performed with the software ADS and Ansoft software and performance of the amplifier were recorded and analyzed. Simulation results indicate a Noise Figure NF below 1.5dB and a gain S21 above 11 dB in all frequency bands and also input and output return loss are below -11 dB for all desired frequency band while drawing 2.5mA current from a 5V power supply. The chip provides a good basis for the realization of WLAN low-cost RF receivers for dual-band operation. These performances situate this receiver among the most competitive low cost and low power RF receivers. All the principles carry out in this work are furthermore transposable to other frequencies and to other transmission standards.


Introduction
In recent years, there has been a growing market for dual band transceivers for various wireless standards. WLANs (wireless local-area networks) have been deployed all over the world as office and ho me co mmunicat ion infrastructures. The increasing demand has motivated the introduction of new W LAN standards such as IEEE 802.11a and IEEE 802.11g to meet various application requirements. Ho wever, the diversificat ion of the W LAN standards poses significant challenges in the design of the RF front-ends. It is desirab le to have a system that can support multi-standard operations wh ile maintain ing a co mp et it ive hardware cost. Us ing conventional receiver arch itectures, simu ltaneous operation at different frequency bands can only be ach ieved by b u ild in g mu ltip le ind ep end ent s ig nal p aths wit h an With so many commun ication standards, one may consider to develop mult i-functional devices, which can operate at several bands and different modes. However, traditional mult ifunction device is often bulky and power hungry in general, wh ich limits the size, weight and the  [3][4][5].
Thus, development of a single-chip multi-function RF receiver with lo w-cost, lo w-power and small fo rm-factor characteristics is in demand [4][5].
In this work, new concurrent dual-band receiver architecture is introduced that is capable of simu ltaneous operation at two different frequencies. These new concurrent dual band LNAs provide simu ltaneous narrow-band input matching and gain at dual frequency bands, while maintaining low noise.
Modern communication applications require easy translation across different co mmunicat ion protocols. This is one of the primary reasons why design of mult i-standard receivers is of such importance in any RF system. Low Noise A mplifiers (LNAs) represent one of the key front-end blocks of RF wireless systems. THE lo w-noise amplifier (LNA) for radio systems is one of the most critical components in the radio front-end. A receiver requires better receiver sensitivity and a lo wer noise figure, for example, an IEEE 802.11a receiver. The expected receiver sensitivity can be achieved by an optimal design of the LNA in terms of a near-to-min imu m noise figure and reasonable power gain over the entire band. On one hand, classical wideband amplifier topologies, e.g., feedback and distributed amplifiers, small area, and lo w cost. On the other hand, an LNA imp lemented with mult iband matching networks provides more degrees-of-freedo m to achieve both a low noise figure and flat power gain without increasing the power consumption. Ho wever, as the dual band input and output matching networks have more circu it components, the LNA noise figure and power gain can be more sensitive to the statistical variat ions of the passive components [3][4], [7].
The linearity o f a Si bipolar junction transistor (BJT) o r a SiGe HBT can b e reliab ly i mp roved us ing a simp le technique based on low-frequency lo w-impedance base termination without degrading gain or NF. However, this techn ique is not effect ive fo r linearizing field -effect transistor (FET) amplifiers. An FET can also be linearized by biasing at a gate-source voltage (Vgs) at wh ich the third-order derivative of its dc transfer characteristic is zero. The bipo lar junct ion transistor was the first solid-state active device to provide practical gain and NF at microwave freq u en cies . In th e sev en ties , b reakth ro ug hs in the development of field-effect transistors (FETs) (e.g., GaAs MESFET) led to higher gain and lo wer NF than bipo lar transistors for the frequencies in the range of several GHz. Currently , ad van ced FETs and b ip o lar trans isto rs still compete fo r lo wer NF and h igher gain at frequencies in excess of 100 GHz. Examples are the high electron-mobility tran s isto rs (H EMTs ), s u ch as p s eu do mo rp h ic h ig h electron-mobility t ransistors (pHEMTs), metamorphic high electro n -mo b ilit y t rans is to rs (M HEM Ts ), as well as heterojunction bipolar transistors (HBTs), built using a variety of semiconductor materials (e.g., GaAs, InP, Si, SiGe) [1].
The design considerations of low-noise amp lifier are mainly in input return loss, power gain, and noise figure (NF), but there are some trade-off between these important characteristics. At the input, network consisting of two filters PBF is used two different frequency bands at 3.9 GHz and 4.48 GHz. The impedance of the input matching network is 50Ω, and the same thing to the output. In this paper, the complete circuit is simu lated by Agilent Advanced Design System (A DS), Section 2 describes the design of the proposed dual-band LNA. Simulat ions results are shown in Section 3 and conclusions are given in Section 4.

Circuit Design
In this paper dual band LNA designs with lu mped and distributed-matching networks are studied. The simplified schematics of the LNA imp lementations are shown in Figure  2. First, sensitivity analyses of the noise figure matching condition in response to frequency are done with regard to passive component tolerances. Then, simulat ions including real-world lu mped passive component tolerances, and for the distributed matching networks, manufacturing process tolerances are performed in advanced design system (A DS) fro m Agilent Technologies [2]. In this section, we will develop a concurrent dual-band receiver arch itecture that can be fully integrated. The objective is to devise a receiver that can simultaneously receive the signal at t wo different frequency bands with maximu m reuse of power. While the input and output of a stand-alone LNA usually needs to be matched to 50Ω.
LNA with dual band distributed matching networks is designed circuit board process aiming for a low noise figure and a flat power gain over the entire 3.7-4.5 GHz bandwidth. As shown in Figure.3, the input matching network of t wo filters BPF the input and adaptation of transistor ATF10136, which will be tuned to 3.9 GHz and 4.48 GHz. the input impedance to 50Ω. The t ransistor ATF10136 is chosen for the purpose of high gain and low noise characteristics. The transistor ATF-10136 is a high performance galliu m arsenide Schottky-barriergate field effect transistor housed in a cost effective microstrip package. Its premiu m noise figure makes this device appropriate for use in the first stage of low noise amplifiers operating in the 0.5-12 GHz frequency range. This GaAs FET device has a nominal 0.3 micron gate length using airbridge interconnects between drain fingers. Total gate periphery is 500 microns. Proven gold based metallizat ion systems and nitride passivation assure a rugged, reliab le device.
The first component of wireless communication receiver is typically a low no ise amp lifier (LNA). It main role is to provide enough gain to overcome the noise of subsequent stages. An LNA not only providing this gain while adding as litt le noise as possible, but also should accommodate large signals without distortion, and frequently must also present a specific impedance, such as 50 Ω , to the input source. In order to get better linearity and noise performance, we should make the noise figure and d istortion as small as possible in LNA part to meet the receiver sensitivity.
Assume that the two operating angular frequencies of the target BPF and LNA are ω1 and ω2 (ω 1<ω 2), respectively. There are two filter BPFs connected with the MN as shown in figure 2. Second, in the Smith Chart, fo r each operating frequency, find the appropriate source and load reflection coefficients, which can satisfy the desired gain and noise figure. Then, design the single-band input A and output B for two single-band LNAs [5]. Figure 3 is concurrent dual-band LNA arch itecture based in the one transistor ATF technology. In the input, there are parallel t wo filters BPF, the proposed low-noise amplifier consists the input matching network which is implemented by the Filter BPF where are L1, C1, L2, C2 and Ls; the main amp lifier is containing M1, the Cdc1, Cdc2 are DC blocking capacitors.
In input matching, for simu ltaneous power and noise matching at dual frequencies, the real part of Zin has matched to 50Ω and the imag inary part of Zin will be zero. The first active element in the receiver chain, the noise figure (NF) o f an LNA p lays a significant role in the overall NF of the receiver, wh ich controls its sensitivity and output signal-to-noise ratio (SNR). Inductive source degeneration is used for input matching. Th is also increases the stability of the LNA through negative feedback at the expense of lower gain [1], [8-[9].
The bias circuit is very critical fo r the overall noise performance of the LNA. The bias current in the LNA does not need to be exact because feedback in the LNA's input stage stabilizes its performance over production. Considering the design goal, the transistor ATF with bias condition of Ic = 2.5 mA and VCE= 5 V is used in the design. In order to improve the stability, an inductor of 0.09 nH is connected with the emitter of the transistor.
In RF wireless receiver, LNA is one of the most crit ical building blocks caused by the noise figure is do minated in 1st stage of the receiver. For LNA design, there are many trade-off between different performances. For examp le, the power gain affects noise figure, the d ie area affect cost, and the power consumption affects the battery life.
The circuit is designed on the substrate FR4 with a relat ive dielectric constant of 4.4 and a thickness of 1.5 mm and two software's Ansoft Designer and ADS is used to simulate the circuit. As shown in Fig.2, the simu lated fract ional bandwidth, Gain and NF after design are 11.95 d B and 1.39 dB at 3.9 GHz, 12.06 dB and 1.34 dB at 4.48 GHz, respectively [5]. For measurement consideration, the output impedance is always designed in 50 Ω in the output buffer. The design considerations of low-noise amplifier are mainly in input return loss, power gain, and noise figure (NF). The resulting Miller impedance therefore acts like a noiseless shunt resistor at the input. By appropriate choose of and it is thus possible to artificially move the LNA's input impedance towards the 50 Ω points in the Smith Chart without affecting its optimu m noise impedance or increasing its minimu m noise figure.
It is crucial to note the fundamental differences between the concurrent and the existing no concurrent approaches. In conventional dual-band LNAs, either one of the two single-band LNAs is selected according to the instantaneous band of operation, or two single-band LNAs are designed to work in parallel using two separate input matching circu its and one separate resonant loads.
We use a general model for an amp lifier in the source impedance (Zs) configurat ion to obtain an equivalent circu it for the input impedance and a general exp ression for the gain at dual frequencies. This equivalent circuit will be used to achieve simu ltaneous power and noise matching in a concurrent dual band LNA.
Theoretically, a large nu mber of passive topologies for and can provide input impedance matching and output impedance matching at dual frequency bands. In this circu it was made input adaptation and output by Smith Chart. The Smith Chart, for each operating frequency, find the appropriate source and load reflection coefficients, which can satisfy the desired gain and noise figure [1][2][3][4][5].
The transistor is not a perfectly unilateral co mponent. These are the mult iple internal feedbacks that create a dependency of the input towards of the output in the real component. It is possible to correct for these effects while working on external feedback that will co mpensate for these phenomena.
When a circu it is unstable, it is often that it has too much gain. This condition associated with a phase condition which in this case did not need to be perfect, is the start of oscillation or a more co mp lex phenomenon still.
To control this setting, it is always possible to add dissipative elements (resistors), the ideal of course is that these resistors dissipate power main frequencies where we expect problems, and disrupt the low point's useful frequencies. We therefore propose to add to the amplifier two resistors of stabilizat ion (input-output), as shown in figure 3.
If the noise factor is too large, this is stabilizing resistance placed in input (the thermal noise is amp lified by the transistor which degrades the high NF). We can then use resonant circuits in the sensitive circuit of frequency stabilizing resistances.
An important design parameter in receiver design, wh ich is the measure of receiver noise, is the noise factor F (also known as NF, when expressed in decibels). The definition of the noise factor of any transducer (e.g., LNA, mixer, filter, etc.) given by [6] is: The value of the noise figure NF characterized by: 10 10.log ( ) NF F = The stability k of an LNA amplifier circuit can also be studied with the help of the Rolett factor as given in Table 1. This is more useful when viewing larger frequency spectral. Where: To design an unconditionally stable LNA amp lifier circuit, which implies that the amplifier remains stable within the entire do main o f the Smith Chart at the selected frequency and the given bias conditions, the following conditions must be met. As well as If an RF amp lifier is determined to be unstable, and its function calls for stability, a stabilising network is needed. One way to stabilise an RF LNA amp lifier is to add a series or shunt resistor to either input or output port, preferably to the output port since a resistor produces noise which is undesirable to amplify.

Results and Discussion
A novel circuit topology for dual-band LNA with a single-input FET, the input matching conditions are satisfied by switching the finger nu mber and the bias voltage of the input transistor. A 3.7/4.48-GHz dual-band LNA was designed and imp lemented. The input parallel resonator and series is made using filter BPF1 a 0.44-pF capacitor and a 7.15-nH inductor parallel and a 0.37-pF capacitor and a 0.13-nH inductor series.
This section presents the simulat ion results of a concurrent dual-band LNA operating at 3.9GHz and 4.48GHz frequency bands for wireless communications. The design is based on the topology of Figure 3; The proposed dual-band LNA ( Figure  3) is simulated with the software ADS and Ansoft software. Figure 4 to Figure 6 illustrate the simu lation results of S-parameters and NF data respectively, as a function of frequency. At 3.9GHz, a NF of 1.39 dB is achieved with 11.95 d B gain. At 4.48GHz, the NF is 1.34 dB with 12.06 d B. The noise figure is higher than that of a single-stage LNA because the input matching network contains two inductors, in which the parasitic resistance will increase the noise figure. The LNA's noise performance is quite satisfactory. Table 2 summarizes the performance of the current design.    The amplifier wo rks at 5 V supply voltage with 2.5 mA current dissipation. Figure 5 shows the gain (S21) of this LNA in d ifferent bands. The maximu m gain is 11.95 d B at 3.9 GHz, and is 12.06 dB at 4.48 GHz. The dynamic range of gain is 11 d B and an interval of about 1 d B at both 3.9 GHz and 4.48 GHz. Figure 6 shows the input return loss and output return loss, respectively, of this LNA. Both are lower than −10 d B in two bands frequency bands showing that the LNA exh ibits good input matching at two frequencies. The maximu m power consumption is 13.8 mW , under a power supply voltage of 5 V. And we have demonstrated its good performance through other software Ansoft post simu lation results.

Conclusions
The new concept of concurrent dual band LNA amp lifiers receivers for wireless microwaves communication systems, with the intention of use as the essential part of a concurrent dual band receiver is designed. One implementation of such new concurrent dual-band receiver arch itecture capable of simu ltaneous operation at two d ifferent frequency bands is analysed. It uses a novel concurrent dual-band LNA, combined with an elaborate frequency conversion scheme to reject the out-of-band signals. A general methodology is also provided to achieve simu ltaneous narrow-band gain and input matching wh ile offering a lo w NF in concurrent dual band LNAs.
The proposed dual-band LNA can be used for the Bluetooth, HiperLA N and Wireless LAN (IEEE 802.11a) communicat ion applicat ions, and is designed based on transistor ATF10136 technology, which has better performance, lower cost and better integration feasibility comparing with other technology. The RF input signals are 3.9GHz and 4.48GHz, respectively. It is operating at supply voltage of 5V. The circuit is simulated using Agilent Advanced design system (ADS) and Ansoft software. By filtering characteristics of input stage, the LNA can selectively receive signals in mu lti-band.