No abstract
ABST1RACT:This paper describes-the first Low Cost, Low Phase Noise SouTce using Silicon Bipolar Transistor, GaAs PHEMT frequency multipliers and a GaAs PHEMT MMIC amplifier to achieve 20 dBm at 36 to 40 GHz. This source includes a Si MMIC prescaler to achieve an L-Band output for easy phase locking of the RF source. Phase noise of better than -85 dBc/Hz at i00 KHz offset has been achieved at 40 GHz to help meet the system requirements of the PCN digital radio link. INTRODIUCTLQN-The wireless revolution has created a number'of new oppoturiities for microwave technology. Point to point radios are now being used to connect cellular and PCN cell sites with the central switching station as well as for private data links. With the saturation at 2,4,6,1O01f1,18 & 23 GHz radio bands, a need for a virgin frequency band was obvious. 38 ± 2 GHz has emerged as an internationally accepted band for the emerging wireless applications. Europe has taken a lead in exploiting this band and is rapidly deploying these radio systems. These radios however need to be cost competitive to leasing equivalent wireline capacity from the local telephone or cable TV company. In the US the FCC recently has licensed 36 to 40 GHz band to cover a rectangular area.In order to produce radios for this huge need, low cost, user friendly and high performance components are a basic necessity. The Tx source is typically the most expensive RF component in the system. A number of different approaches have been used in the transmitter design of radios above 18 GHz. The most common approach has been the use of fundamental Gunn Oscillators.Till recently the three terminal device technology, though available for years have not been cost competitive with the Gunn solution. Gunn oscillators have inherent problems of microphonics, cold start, consistency, mechanical tolerance requirement, DC power, space and weight requirement. Multiple Gunn oscillators are required to cover the full band. On the other hand Gunns have excellent phase noise and can generate the required 17 to 20 dBm power using a single device. GaAs MMIC prices at mmw frequencies have now come down to be an attractive alternative. A recent approach used a fundamental GaAs MMIC VCO with dual varactors1, but has inadequate phase noise and linearity for easy application in the high level FSK modulation scheme. Fundamental oscillators have an additional disadvantage of requiring complex harmonic sampler based phase locking techniques.DESlGN APPROACH: In this paper a unique approach optimizing the use of silicon and GaAs technologies for a high performance and cost competitive solution for the Tx source at 38 GHz is presented. An optimum use of Silicon and GaAs technology particularly MMICs, has helped develop a low cost and high performance solution for this new application. 548 Figure 1 shows a block diagram of the proposed configuration. This_-source simiutaneously provides an L-Band signal in addition to-the final frequency. A low phase noise xC-Band Si Bipolar VCO is followed by two GaAs frequency...
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