Design & Development of S-Band Ultra low Noise Amplifier

Design & Development of S-Band Ultra low Noise Amplifier

Amit Tiwari¹, R.C.Yadav² Ankit Niranjan³

D&E-Microwave Components,

Bharat Electronics Limited, Ghaziabad-201010

Abstract-A highly stable wide band ultra Low Noise Amplifier with Minimum noise figure of 0.7dB & minimum gain of 44 dB has been developed & presented in this paper. Balanced amplifier configuration approach has been used in this discussed design to have stable noise figure over the wide bandwidth. The LNA Module has protection against overvoltage & reverse polarity. This paper gives complete design & measurement results of developed LNA.

Keywords: LNA, Noise Figure, Gain, Balanced Amplifier

1. INTRODUCTION

   The balanced amplifier approach was first reported by Engelbrecht and Kurokawa [1] as a way of providing a good input match when an amplifier was tuned for optimum noise performance in 1965, and in a subsequent paper by Kurokawa

   [2] discussed the theory of the balanced amplifier.

   The ideal amplifier would have constant gain and good input matching over the desired frequency bandwidth. Conjugate matching will give maximum gain only over a relatively narrow bandwidth, while designing for less than maximum gain will improve the gain bandwidth, but the input and output ports of the amplifier will be poorly matched. Balanced amplifier configuration has trade off of this problem. Two amplifiers having 90° couplers at their input and output can provide good matching over an octave bandwidth, or more. The gain is equal to that of a single amplifier, but the design requires two transistors and twice the DC power.

   Fig 1 Balanced Amplifier using 90 ° hybrid couplers.

   Fig 1 shows a Balanced Amplifier configuration [3] with a 90° coupler. A fairly flat gain response can be obtained if the amplifier is designed for less than maximum gain, but the input and output matching will be poor. The balanced amplifier circuit solves this problem by using two 90º couplers to cancel input and output reflections from two identical amplifiers. The first 90° hybrid coupler divides the input signal into two equal- amplitude components, with a 90° phase difference, which drives the two amplifiers. The second coupler recombines the

   amplifier outputs. Because of the phasing properties of the hybrid coupler, reflections from the amplifier inputs cancel at the input to the hybrid [4], resulting in an improved impedance match; a similar effect occurs at the output of the balanced amplifier. The gain bandwidth is not improved over that of the single amplifier sections. This circuit has advantage that individual amplifier stage can be optimized for gain flatness or noise figure, without concern for input and output matching. Reflections are absorbed in the coupler terminations, improves input/output matching, as well as the stability of the individual amplifiers. The circuit provides a graceful degradation of a 6 dB loss in gain if a single amplifier section fails. Bandwidth can be an octave or more, primarily limited by the bandwidth of the couplers.

   Besides stability and gain, another important design consideration for a microwave amplifier is its noise figure. In receiver applications especially, it is often required to have a preamplifier with as low a noise figure as possible, since, the first stage of a receiver front end has the dominant effect on the noise performance of the overall system.

   Generally it is not possible to obtain both minimum noise figure and maximum gain for an amplifier, so some sort of compromise must be made. This can be done by using constant-gain circles and circles of constant noise figure to select a usable trade-off between noise figure and gain. A white paper on practical design considerations for LNA designs by Tim Das gives good insight for practical designs [5]

2. DESIGN THEORY

   The noise figure of a two-port amplifier can be expressed as [6]

   Where the following definitions apply:

   YS = GS + j BS = source admittance presented to transistor.

   YOPT = optimum source admittance that results in minimum noise figure.

   F min = minimum noise figure of transistor attained when Y S = Y opt.

   RN = equivalent noise resistance of transistor.

   GS = real part of source admittance, and the admittances are often expressed in terms of Reflection co efficient as follows

   ( ) (2)

   () (3)

   Design of LNA proceeds with the specification of quantities

   F min , opt and R N for a given Transistor. Then Noise figure parameter N is computed [7].

   (4)

   & the parameters for the Noise Figure circles are obtained as below:

   The optimum solution is found in conjunction with the Constant gain circles on the Smith chart.

3. DESIGN APPROACH & METHOD

   The design methodologies and strategies discussed broadly apply to amplifiers based on discrete devices like BJT/FET. To achieve ultra low noise, the input stage HEMT was matched at the impedance of minimum noise figure of HEMT. The output stage HBT was matched to 50 for getting high gain & low VSWR. This provides compact, cheaper & highly stable design using the cascaded configuration of three MMICs (one HEMT & two HBT).

   Fig 3 shows RF schematic of ultra low noise amplifier. In this low cost HEMT CGY2105XHV, with 0.25dB minimum noise figure, has been used in balanced configuration approach.

   Fig.2 ADS Simulation for Balanced Configuration

   HEMT gives 17.2 dB typical gain & 0.5 dB noise figure in this configuration. Subsequent amplification is being done by standard low cost Gali 5+ InGaP HBT Monolithic amplifier with same typical gain & 3.5dB noise figure.

   ADS Simulation of LNAs shows Noise figure of 0.6 dB with 47.2 dB typical gain.

   Fig.3 Schematic of ultra low noise amplifier module.

   All MMICs are configured for operation at +5 Volts & required negative voltage is also being generated internally in discussed design. For HEMT bias, sequencing has been implemented in design along with overvoltage protection. Frequency of hybrid used in present design limit the operational frequency from 2.3 to 2.7 GHz otherwise same can be used over bandwidth of DC to 4GHz. Fig 4 shows bias circuit for discussed LNA design.

   Fig.4 Bias circuit of LNA

   PCB has been designed using Rogers Substrate RO4350, 20mil. Proper filtering has been done in power supply to avoid any noise introduction in circuit. Design & simulation tools like ADS, App-cad, Altium, Solid Works etc have been used in analysis/calculations & mechanical housing design for the developed LNA. Fig 5 shows developed LNA Module.

   Fig. 5 Developed LNA module.

4. EXPERIMENTATION & RESULTS Measured results of Ultra Low Noise Amplifier shows 0.7

   dB Noise figure with 46 dB gain. Developed LNA operates over the temperature (-30°C to +60 °C). The LNA module weighs less than 200 gm.

   Measurement data in 2-3 GHz range is shown in Fig 6 & 7 respectively for noise figure & gain variation over frequency.

   Fig.6 Noise Figure Vs Frequency

   Fig.7 Gain Vs Frequency

5. CONCLUSION

Ultralow Noise Figure, compact size, high gain, wide band frequency of operation & stable behavior, make this design attractive for various applications. Developed module has been evaluated in system for SOTM (Satellite on the Move) application successfully in vehicle to receive satellite link at 2.56-2.59 GHz frequency

ACKNOWLEDGEMENT

Author would like to give special thanks to Mrs. Anita Milind (AGM-MWC) for her guidance & Sh. Charan Sinh GM (R) & Unit Head (BEL-Ghaziabad) for giving permission for publication of this paper in journal.

REFERENCES

1. R. S. Engelbrecht and K. Kurokawa, "A Wideband Low Noise L-Band Balanced Transistor Amplifier," Proc. IEEE, vol. 53, no.3, pp. 237-247, March 1965.

2. K. Kurokawa, "Design Theory of Balanced Transistor Amplifiers," Bell System Tech. J., vol. 44, pp. 1675-1698, Oct. 1965.

3. Ulrich L. Rohde & David P. Newkirk RF Microwave Circuit design for wireless applications pp148, A Wiley-Interscience Publication

4. Dr. E.H. Fooks & Dr. R.A Zakeravicious Microwave engineering using Micro strip circuits pp168, Prentice hall

5. Tim Das, White paper on Practical considerations for Low Noise Amplifier Design, Freescale Semiconductor, 2013.

6. Brian Hughes, Designing FETs for Broad Noise Circles, IEEE Transactions on Microwave Theory and Techniques, vol. 41, no. 2, pp. 190198, 1993

7. John Rogers, Calvin Plett, Radio Frequency Integrated Circuit Design, pp 16, Artech House,2003.

8. Data sheet & application notes of CGY2105XHV of OMMIC

9. Data sheet & application notes of Gali 5+ of mini circuits.

10. Datasheet & application notes of MAX881 by Maxim.

AUTHORS

¹Amit Tiwari has graduated his Bachelor in Engineering in Electronics & Communication & Master of Technology in Microwave Engineering from IT-BHU. He has 17 years of R&D experience. He served MITS & Institute of Engineering, Jiwaji University

Gwalior as an assistant professor. He is currently working as Deputy Manager, in Development & Engineering-Microwave Components of Bharat Electronics Limited, Ghaziabad. He has designed & developed C-Band Airborne RF Transceivers, IFF Tx-Rx Unit for AEW&CS, IFF Transmitters for Radars, SSPA, Receivers & its components etc for Data link & Radar applications. He has received awards for innovative efforts, six sigma, technical symposiums etc.

²R. C. Yadav did his Master of Technology in Microwave Engineering from South Campus, Delhi University, in 1992. He served various organization for more than 23 years out of which 5 years in Institute of Microelectronics, Singapore, He is

currently working as Sr. Deputy General Manager, Development & Engineering-Microwave Components of Bharat Electronics Limited, Ghaziabad. He is recipient of Rakshamantri award for R&D efforts. He has been involved in design of IFF Radar transmitters & Receivers etc.

³Ankit Niranjan is a B.Tech in Electronics Engineering from KNIT, Sultanpur. He joined BEL in Nov 2014 in D&E Microwave Components Division Ghaziabad. In BEL he has received awards for innovative efforts.