Research On Sige HBT Ultra-wideband Low Noise Amplifier

As a novel Radio Frequency(RF) devices, SiGe heterojunction bipolar transistor(HBT) are gradually used in design of ultra-wideband low noise amplifier(UWB LNA)due to comparable gain and frequency characteristics to the III-V devices, and highintegration with existing silicon technology. Two critical research aspects of SiGeHBT UWB LNA are device and circuit. As well known, good device performance isfundamental to achieve good performance of circuit. In one hand, the investigation offactors which affect device performances never stop including operating frequency,bias condition, geometry parameters, fabrication technology and so on. Meanwhile,researchers are also pay great attention to noise model of device and extractionmethodology of noise parameters. In another hand, the market requirements for smalldie area and high gain of UWB LNA push the improvement techniques researches toachieve simultaneously excellent noise and impedance characteristics withoutinductor, to offer the high gain with good gain flatness in wide frequency band.In this dissertation, researches are focus on SiGe HBT and SiGe HBT UWB LNA,the main works can be summarized as follows:Firstly, in order to solve the problem that noise model of SiGe HBT used in SPICEdesign tool at present ignores the RF correlation, the novel noise model consideringRF correlated noise is developed. In the novel noise model, the impact of collector-base junction space charge region(CB SCR) delay effect on base noise current sourceand collector current source is taken into account. And the novel model is representedby popular HICUM model, as well as be compiled using Verilog-A(the wholecompiling program is given in appendix A). Therefore, the novel noise model couldbe embed into any standard CAD design tools, and compatible with other existingmodels, such as DC model, AC model, frequency model and so on. The novel noisemodel and SPICE noise model are compared with measured results of SiGe HBTs.The results show that the noise parameters extracted from the novel noise modelagrees well with device measurement.Secondly, Z parameters extraction methodology of transistor noise parameters isproposed for the first time. New methodology directly builds the relationship betweennoise parameters of devices and port impedance parameters of circuits without Y-Zconversion process, which is clearly an attractive benefit compared with traditional Yparameters extraction methodology. It is much more convenient to achieve thesimultaneous noise and impedance matching of LNA.Thirdly, the impact of frequency(f), collector current(IC) and geometry parameterson the minimum noise figure(NFmin) of RF SiGe HBT are examined theoretically and experimentally. It is showed that NFmingrows up parabolically with increase offrequency. Hence, three critical conditions of high current gain(β), low baseresistor(RB) and high cut-off frequency(fT) to optimize NFminare given by analyzingthe tangent slope of the parabola curve. Furthermore, there exists an optimum ICatwhich transistor achieves the minimum NFminfor a given operating frequency. Inaddition, it is beneficial for reducing the NFminby slightly increasing the ratio ofemitter length to emitter width, gently reducing spacing between emitter stripe andbase stripe, and slimly adding base stripes.Fourthly, the technique relating to achieve simultaneous noise and both input andoutput ports impedance matching(SNBIOM) is proposed by adopting compositenetwork of L-C and R-L-C based on improved technique of simultaneous noise andsingle input port impedance matching. Then the impacts of the novel noise model onC waveband RF LNA designs are comprehensively investigated, which includedesigns of noise matching, input conjugate impedance matching and SNBIOM. It isfound that the novel noise model is more attractive to easily achieve noise matching,impedance matching, and SNBIOM compared with traditional SPICE noise model.Furthermore, the noise model even gives rise to IIP3improvement for SNBIOMdesign of LNAs with voltage bias and current bias without negative effects on highgain and high stability. Especially, the improvement is more dramatical for the LNAwith current bias.Fifthly, the design techniques for SiGe HBT UWB LNA to achieve high gain andsmall die area are investigated by taking advantage of the novel composite feedbackresistive without using inductor. First of all, the improved technique of Darlingtonpairs(DP) is analyzed to achieve high gain. Then, in order to guarantee flatness of gain,the technique for gain flatness enhancement is investigated by comparison betweenbypass inductor and capacitor compensation techniques. It is found that bypasscapacitor compensation technique is better. Finally, for the first time, the novelcomposite resistive feedback technique is proposed in conjunction with DP techniqueand bypass capacitor compensation technique so as to obtain excellent performanceincluding SNBIOM, high gain and high gain flatness, and small die area without usinginductor. This novel SiGe HBT UWB LNA shows that S21is as high as24.33dB withgain flatness of±0.7dB, S11is as low as-21dB, S22is less than-14dB, NF is highlyclose to NFmin, which as low as3.7dB, and Mul_l keeps always larger than1in theband from3GHz to10GHz. Due to absence of spiral inductors, the die area of theSiGe HBT UWB LNA is only0.18mm2(0.45×0.40mm2).Finally, the fabrication processes suitable for SiGe HBT monolithic microwaveintegrated circuit (MMIC) are developed based on the state of the art integrated circuittechnology. Meanwhile, the plane fabrication processes of RF SiGe HBTs for MMICapplication are examined individually, and a series of transistors are fabricated successfully. Due to good DC performance, fT/fmax=7/6.93GHz, NF as low as2.5dBwithin1.2GHz, the fabricated devices are suitable as active devices of L, S, and Cwaveband RF LNA.By adopting developed MMIC processes, SiGe HBT UWB LNA MMIC with thenovel composite resistive feedback is fabricated. Meanwhile, SiGe HBT DP LNAMMIC with single resistive feedback is also fabricated as a counterpart circuit. Theabsence of inductor leads to a small chip area of0.2mm2(0.5×0.4mm2). Initialmeasured results show that, compared with SiGe HBT DP LNA MMIC, SiGe HBTUWB LNA MMIC achieves higher gain, lower NF and better impedance matching,GAas high as24.7dB, NF as low as2.8dB in the band from0.2GHz to1.2GHz, aswell as S21is up to25.5dB, and both S11and S22are lower than-10dB in the band from0.5GHz to3.5GHz.