High Gain Cascaded Low Noise Amplifier Using T Matching Network

Transcription

1 High Ga Cascaded ow Noise Amplifier Usg T Matchg Network Othman A. R, Hamidon A. H, Abdul Wasli. C, Tg J. T. H, Mustaffa M. F Faculty of Electronic And Computer Engeerg Universiti Teknikal Malaysia Melaka. O Box 1600, Hang Tuah Jaya Melaka, Malaysia Keywords: Amplifier, ow Noise Amplifier, Radio Frequency. Microstrip Abstract This project presents a design of high ga cascaded low noise amplifier (NA), which operates at 5.8 GHz frequency for WiMAX application. The NA designed used T matchg network consist of lump reactive elements and microstrip at the put and output impedance. A cascaded NA is developed this project contributes a high ga of 36.8 db with overall noise figure of 1.3 db. The overall measured bandwidth measures is 1.40 GHz with parameters 11, 1 and measured are -11.4dB, -39.1dB and -1.3dB respectively. The put sensitivity of the NA is -80dBm which compliant with the IEEE WiMAX application. The NA used FET transistor FX 76 from Euda Inc. 1 Introduction The first stage of a receiver is typically a low noise amplifier (NA), whose ma function is to provide enough ga to overcome the noise of subsequent stages. Many researchers have been done CMO NA area from 900 MHz to 9 GHz [1-4]. In the literature there are many NA work designed GaAs and bipolar technology [5-8]. In this paper a low voltage, low power and wideband seudomorphic High Electron Mobility Transistor (HEMT) NA at 5.8 GHz is designed and simulated usg Ansoft Designer and AD 000A. As a design tool sensitivity analysis gives a measure of sensitivity for a NA circuit performance due to change the active element to be HEMT and assistg the designer choosg adequate circuit elements tolerances [9]. uch sensitivity analysis of NA is very beneficial for makg appropriate design tradeoff. Four NA designed Usg HEMT with two operation condition. The first two NA is designed with the same parameters published [1]. The second Two NA is optimized to achieve a mimum noise figure with maximum ga available. The progress of wireless communication services has creased the need for NA designed which has higher capability providg higher gas, better put sensitivity and mimize noise level. It is desirable to combe two or more standards one mobile unit for overall capacity enlargement, higher flexibility and roamg capability as well as backward compatibility. Moreover multi standard RF receiver will allow access to different system providg various services. These are the cause of the vestigation to crease the bandwidth of the systems for multi-band multimode operation. In WiMAX system, NA designed for receiver system are breakg the bonds of wired connections separated buildgs to be connected the area that the wired bridge is impossible to be deployed and stalled. WiMAX wireless technology can be more economical and efficient than stallg wired networks. With the current technology of Orthogonal Frequency Division Multiplexg (OFDM) adopted IEEE WiMAX standard, the system can provide high data rate up to 70 Mbps []. The RF receiver WiMAX system plays a paramount role for convertg baseband signal from the RF signal so that the system can be communicatg wirelessly. Therefore, the performance of the WiMAX system also relies on the RF front end receiver system such as NA where it must be well designed to mimize the noise level (or distortions) the system.[3]. The approach taken designg the amplifiers volves a series of chronological steps. No design is complete without some desired goals. The design specifications for the low noise amplifier were shown Table 1.1: 1

2 arameter NA Ga db > 35 Frequency 5.8 GHz NF db < 3 Matchg Technique Microstrip and lump reactive element VWR 1.5 Bandwidth MHz >1000 (5.8 GHz Centre) Input sensitivity - 80 dbm (WiMAX) Table 1.1: Design specifications for NA With refer to Table 1.1 the ga targeted for the NA is more than 35 db. This ga is necessary to amplify week signals and separated from the noise. The amplifier will mata noise figure less than 3 db and provide bandwidth of 1000 MHz. The put sensitivity for the NA is set at - 80dBm compliant with the standard WiMAX application. transmission from source to load. The targeted specification amplifier is shown Table ower Ga everal power gas are defed to understand operation of super high frequency amplifier, as shown Figure., power gas of port circuit network with power impedance or load impedance at power amplifier represented with scatterg coefficient are classified to Operatg ower Ga, Transducer ower Ga and Available ower Ga.[4],[5] Theoretical Description Basically, for a design of amplifier, the put and output matchg network are designed to achieve the required stability, small signal ga, and bandwidth [4]. uper high frequency amplifier is a typical active circuit used to amplify the amplitude of RF signal. Basic concept and consideration design of super high frequency amplifier is presented below. For the NA design the formulae and equation were refer to [1]. Figure.1 shows a typical sglestage amplifier cludg put/output matchg networks. Figure.: I/O circuit of -port network. Operatg ower Ga Operatg power ga is the ratio of power ( ) delivered to the load (Z ) to power ( ) supplied to port network. ower delivered to the load is the difference between the power reflected at the output port and the put power, and power supplied to -port network is the difference between the put power at the put port and the reflected power. Therefore, Operatg ower Ga is represented by G ower delivered to the load power supplied to the amplifier 1 Γ 1 Γ Γ (1) Figure.1: Typical amplifier designed In short, basic concept of high frequency amplifier design is to match put/output of a transistor for high frequencies havg parameters [] frequency characteristics at a specific DC-bias pot with source impedance and load impedance. I/O matchg circuit is essential to reduce unwanted reflection of signal and to improve efficiency of Where, Γ dicates reflection coefficient of load at the put port of -port network and Γ s is reflection coefficient of power supplied to the put port.

3 .3 Transducer ower Ga Transducer ower Ga is the ratio of avs, maximum power available from source to, power delivered to the load. As maximum power is obtaed when put impedance of circuit network is equal to conjugate complex number of power impedance, if Γ Γ s, transducer power ga is represented by ower delivered to the load G power supplied to the amplifier 1 ( Γ )( Γ ) (1 Γ )(1 Γ ) ( Γ Γ ) Where, 11 Γ dicates load reflection coefficient. 1 1 ().4 Available ower Ga Available ower Ga, G A is the ratio of avs, power available from the source, to avn, power available from - avn port network, that is, G A. ower ga is avn avs when Γ Γ * s. Therefore Available ower Ga is given by: ower delivered to the load GA power supplied to the amplifier avn Γ 1 1 Γ Γ avs 11 (3) That is, the above formula dicates power ga when put and output are matched..5 Noise Figure ignals and noises applied to the put port of amplifier are amplified by the ga of the amplifier and noise of amplifier itself is added to the output. Therefore, NR (ignal to Noise Ratio) of the output port is smaller than that of the put port. The ratio of NR of put port to that of output port is referred to as noise figure and is larger than 1 db. Typically, noise figure of -port transistor has a mimum value at the specified admittance given by formula: F F m R + G N Y s Y opt (4) For low noise transistors, manufactures usually provide F m, R N, Y opt by frequencies. N defed by formula for desired noise figure: N Γs Γopt F Fm 1+ Γ opt Γ 4RN / Z0.6 Design NA (5) From equation (1) to (5), the related power ga and noise figure for sgle stage NA are calculated. By usg AD 005A, the noise figure circle is outside the unit circle and the VWR recorded is.179. From simulation, it was recorded that the amplifier ga 1 is 17.3 db. The put sertion loss 11 is -6.8dB and the output sertion loss is -7.60dB. The reflected loss 1 is db and the noise figure is 1.16 db. These values were with the design specification and were accepted. The overall performance of the low noise amplifier is determed by calculatg the transducer ga G T, noise figure F and the put and output standg wave ratios, VWR IN and VWR OUT. The optimum, Γopt and Γ were obtaed as Γ opt j and Γ j The calculated ga for the NA was 19.3 db, which correspond to a noise figure of db. The put matchg load Γ opt is required to provide high-loaded Q factor for better sensitivity. A T-network was used to match the put impedance. The elements of T-network can be realized the form of lump reactive elements and microstrip le impedance. Usg mith Chart matchg technique, the component values are shown Table.1. The DC block capacitor is selected for the circuit and the value is recommended at least 10 times from the C 1. For this reason 7.5 pf capacitors are selected as bypass capacitors. With these components, the schematic circuit for sgle stage NA is shown Figure.3. Components C 1 C B Values 3.60 nh 0.88 nh 0.67 nh 0.75 nh pf 7.5 pf Table.1: NA Amplifier parameters 3

4 Figure.3: The schematic circuit for sgle stage amplifier To achieve the targeted overall ga of 35 db, it was decided to design a cascaded amplifier usg similar stages to double the NA ga. The simulation of cascaded amplifier will be discussed section below. 3 imulation The cascaded amplifier is then redrawn and simulated aga usg Ansoft Designer V and the related frequency response and output ga is shown Figure 3.1. Figure 3.: Frequency Response versus Ga The parameters output is shown Figure 3., it is observed that the ga archive 1 is db at 5.8 GHz frequency and the correspondg put sertion loss 11 is db, reflection loss 1 is db and output sertion loss is db. The stability factor after matchg load is shown Figure 3.3 and Figure 3.4. Figure 3.3 shows the stability circle lies side mith Chart diagram while Figure 3.4 shows the obtaed stability factor k is 1 and VWR observed is These parameters are compliant with the targeted specifications of the amplifier for unconditional stable condition k is 1 and VWR is targeted as 1.5. The noise figure output observed is 1.37 db for the cascaded amplifier as shown Figure 3.5. Figure 3.1: Cascaded NA Figure 3.3: tability circle refer to mith Chart 4

5 Figure 3.6: NA ayout This designed circuit is sent for fabrication and the NA layout is shown Figure 3.6 Figure 3.4: tability factor k for matched load 4 Measurement With refer once to measurement setup shown Figure 4.1, the parameter of the amplifier; whereas 11, 1, 1 and are measured usg the network analyzer. The ga of the amplifier is measured usg the setup Figure 4.. The noise figure values and 3 db bandwidth are obtaed from setup Figure 4.3. Before all measurement was recorded, a standard procedure of calibration was followed to ensure that the measurement tools were calibrated. Figure 3.5: Noise Figure parameter for matched load The simulated parameters of the amplifier is tabulated Table 3.1 arameters NA imulated NA Input reflection 11 db Return oss 1 db Forward Transfer 1 db Output Reflection loss db Noise Figure NF db * < Bandwidth MHz >1000 > 1000 Figure 4.1: Measurement setup for device under test for Measurement usg Network Analyzer Table 3.1: arameter Output and Targeted arameters of Cascaded NA Figure 4.: Measurement setup for device under test for Frequency Response. 5

6 than 1 GHz. The measured parameters for the NA were also compliant with the formulae (1) to (5) usg MathCAD analysis. 6 Conclusion Figure 4.3: Measurement setup for device under test for 5 Result Noise Figure The result for NA RF front-end module is presented Table 5.1. Table 5.1: arameter result for NA arameters Targeted Measured Input Reflection 11 db <-10 db Return oss 1 db <-10 db Forward transfer 1 db >35 db 36.8 Output Reflection db <-10 db -1.3 NF db * <3 db 1.3 BW MHz > * Measured usg noise figure analyzer Telecom R&D. From the tabulated values, the 11 parameter measured is 11.4 db. This is -1.4 db less than targeted which is better and acceptable. measured is -1.3 db which is less than targeted and acceptable. The return loss required 1 obtaed is less than -39 db. The related measured ga 1 for the NA amplifier is 36.8 db measured usg the setup Figure 4.3. The noise figure values obtaed from setup Figure 4.4 is 1.37 db which complied with the targeted value of less 3 db. The use of T lump reactive element and microstrip le matchg technique at the put of the NA contributes the best performance for the amplifier. This matchg technique was used to provide high-loaded Q factor for better sensitivity and thus mimized the noise figure [6]. The elements of T-network were realized the form of lump reactive elements and microstrip le impedance. The 3 db bandwidth for the amplifier is measured usg setup Figure 4.3. The 3dB bandwidth obtaed is 1.4 GHz compliant with targeted result of more A low noise amplifier has been simulated and developed successfully with IEEE standard WiMAX. It is observed that the simulated and experiment results have not much different. It observed that the ga of the simulated analysis is 34. db and the experimental value is 36.8 db. It is important to take note when designg the amplifier to match the amplifier circuits. The 5.8GHz NA has been developed successfully and the circuit cab contributed to the front end receiver at the described frequency. For better performance ga of the amplifier, it can be achieved by creasg the number of stages to improve the ga and noise figure of the design. Higher ga will expand the coverage or communication distance. Acknowledgement The authors would like to thank UTeM which has fancially sponsored this research project under short-term research grant. References [1] Xuezhen Wang and Robert Weber, Design a CMO ow Noise Amplifier (NA) at 5.8 GHz and its sensitivity analysis, 11th NAA ymbosium, 003. [] Institute of Electrical and Electronic Engeerg (IEEE). 1999, IEEE tandard: art 11, Wireless AN Medium Access Control (MAC) and hysical ayer (HY) specifications: High-speed hysical ayer the 5 GHz Band. IEEE 80.11a. [3] Jui-Hung Yeh, Jyh-Cheng Chen, Chi-Chen ee. Oct./Nov. 003, WAN standards :. otentials IEEE.. (4): pg16 [4] Man & Tel Co.td,006,MW-000 Microwave Communication Traer,Manual Traer [5] David M. ozar. 001, Microwave and RF Wireless ystem. Third Avenue, N.Y.: John Wiley &ons,in [6] Bahl, I. & Bhartia,. (003). Microwave olid tate Circuit Design, nd Edition, J Wiley, pp