2000 Silicon Germanium (SiGe) Technology Enhances Radio Front-End

The Datasheet Archive - 100 Million Datasheets from 7500 Manufacturers.

2000 Silicon Germanium (SiGe) Technology Enhances Radio Front-End

Datasheet Thumbnail

Top Searches for this datasheet

BASESTATIONS WIRELESS INFRASTRUCTURE WIRELESS, CABLE
2000
Silicon Germanium (SiGe) Technology Enhances Radio Front-End Performance
This application note describes silicon germanium enhances performance applications. Giacoleto model used analyze noise effects. Wider gain bandwidth SiGe technology shown provide lower noise performance. impact SiGe linearity explored. Three parameters increasingly important cellular handsets other digital, portable, wireless communication devices. power consumption lightweight batteries lend autonomy device, higher front-end sensitivity increases reception distance, greater front-end linearity direct impact admissible dynamic range. This last parameter gaining emphasis with advent nonconstant-energy modulation schemes such /4DQPSK 8QAM. Silicon Germanium (SiGe) newest innovation simultaneously improving power consumption, sensitivity, dynamic range receiver. GST-3 high-speed process technology based silicon germanium (SiGe), which features transition figure (fT) 35GHz. typical front-end block diagram (Figure shows performance possible with Silicon Germanium technology (1.9GHz) combination mixer low-noise amplifier (LNA).
Figure Typical radio input circuitry includes low-noise amplifier mixer.
Silicon Germanium Noise Performance
main contribution noise figure down-conversion link noise created LNA's first transistor input stage. Noise figure (NF) serves figure merit networks, compare noise actual network with that ideal noiseless network. noise factor amplifier other network with power gain equal POUT/PIN expressed measure degradation signal-to-noise ratio (SNR) between input output ports network, typically expressed 10log10F. Therefore, Input SNR/Output (PIN/NIN)/(POUT/NOUT) NOUT/(NIN. concerned with thermal noise (also called Johnson noise white noise) shot noise (also called Schottky noise).
detailed high-frequency equivalent model bipolar transistor (the Giacoleto model-see Figure helps understanding this noise generated. model also shows Silicon Germanium technology help reduce LNA's front-end noise figure.
Figure This detailed npn-transistor model (the Giacoleto model) simplifies analysis frequency effects.
Silicon Germanium Thermal Shot Noise
Within conducting medium whose temperature above absolute zero (0°K), random motion charge carriers produces random noise-producing voltages currents. rising conductor temperature increases charge-carrier velocity these random motions, which increases noise voltage. thermal noise generated parasitic base resistance transistor Vn(f) where Vn(f) equals voltage spectral noise density V2/Hz. Boltzmann's constant (1.38 10-23 Joules/Kelvin), absolute temperature degrees Kelvin 273°). Shot noise consequence particle-like nature charge carriers. current flow semiconductor often regarded constant every instant, current consists individual electrons holes. Only time-average flow these charge carriers appears constant current. fluctuation number charge carriers produces random current that instant, which known shot noise. spectral noise density shot noise base current Inb(f) 2qIb 2qIc/, where current spectral noise density I2/Hz, base dc-biasing current, electron charge (1.6 10-19 coulombs), transistor's current gain. Thus, total noise spectral density generated transistor's input stage thermal shot noise: RSOURCE 2qIc/ Maxim's Silicon Germanium SiGe process, GST-3, created extension GST-2 bipolar process with transition frequency 27GHz) doping transistor bases with germanium. result important decrease significant increase transistor beta. combined effect these changes better noise figure Silicon Germanium transistor (vs. that silicon transistor with similar collector current). Typically, transistor noise figure expressed Vn2(f) RSOURCE Inb2(f) RSOURCE Because RSOURCE Vn(f)/Inb(f) gives minimum noise figure Si-bipolar well Silicon Germanium technology, full
benefits Silicon Germanium process obtained designing with source impedance close this value. Another important aspect wireless design derating noise figure frequency. power gain typical transistor similar upper curve Figure This curve surprising, considering equivalent transistor circuit Figure effect, model lowpass filter whose gain falls octave. maximum theoretical frequency which common-emitter current gain unity (0dB) called transition frequency (fT). LNA's gain depends directly derating noise figure NOUT/(NING)] begins with rolloff gain.
Figure Silicon Germanium (SiGe) bipolar transistors exhibit high gain noise. GST-3 Silicon Germanium process improves noise figure high frequencies, consider that adding germanium p-silicon base transistor reduces bandgap 80mV 100mV across base, creating strong electric field between emitter collector junctions. rapidly sweeping electrons from base into collector, this electric field reduces transit time (tb) required carriers cross narrow base. other factors held constant, this reduced provides approximate increase identical-area transistors, Silicon Germanium device achieves given with one-half one-third current required GST-2 device. Higher reduces high-frequency noise, because rolloff occurs higher frequency.
Ultra-low-noise Silicon Germanium (SiGe) Amplifier (MAX2641)
Silicon Germanium MAX2641 offers advantages over silicon-bipolar LNAs, whose falls frequencies approaching 2GHz limit (i.e., 1.5dB 1GHz 2.5dB 2GHz). High reverse isolation Silicon Germanium device also allows tuning input-matching network without affecting output matching, vice versa. Silicon Germanium MAX2641 optimized operation 1400MHz 2500MHz range, with typical performance that includes 14.4dB gain, -4dBm input (IIP3), 30dB reverse isolation, 1.3dB noise figure 1900MHz (Figure Available 6-pin SOT23 packages, operates from +2.7V +5.5V single supply, draws 3.5mA, internally biased. only external components typically required two-element input match, input output blocking capacitors, bypass capacitor.
Figure Note very noise figure this Silicon Germanium integrated-circuit low-noise amplifier.
Silicon Germanium Linearity
addition noise finite bandwidth, communication systems limited signal distortion. system's usefulness depends dynamic range (i.e., signal range process with high quality). Dynamic range dictated noise figure, whose lower limit defined sensitivity level whose upper limit defined acceptable maximum level signal distortion. Achieving optimum dynamic range involves trade-offs among power consumption, output signal distortion, level input signal with respect noise. typical receiver block diagram (Figure shows relative importance noise figure linearity mixer. Because input supplied directly very low-level signal from antenna, dominant parameter. mixer, amplified signal from output, linearity dominant parameter. output never exact replica input signal because transistor perfectly linear. output signal always includes harmonics, intermodulation distortion (IMD), other spurious components. Figure second term POUT equation called second harmonic second-order distortion, third term called third harmonic third-order distortion. Both characterized driving device input with signal consisting tone pure sinusoidal tones closely spaced frequency. Third-order intermodulation distortion MAX2681, example, characterized with 25dBm signal consisting tones 1950MHz 1951MHz.
Figure two-tone test characterizes harmonic intermodulation distortion.
graphic frequency-domain representation POUT equation shows that output consists fundamental frequencies second harmonics third harmonics second-order intermodulation product IM2, third-order intermodulation product IM3. Figure also shows that cellular handsets other systems with narrow-band operating frequencies (i.e., tens megahertz, less than octave), only spurious signals fall within filter passband. result distortion desired signals associated with POUT equation levels output power, coefficient directly proportional input signal amplitude, K2A2 proportional square, K3A3 proportional cube input amplitude. Thus, plot each scale straight line with slope corresponding order response. Second- third-order intercept points often used figures merit. higher intercept point, better device amplify large signals. higher power levels, output response compressed therefore deviates from response fundamental. This deviation point (Figure defined com- pression point, situated where output signal compresses (G1dB 1dB) with respect extrapolation linear portion curve. From MAX2681 data sheet, POUT frequency above 1900MHz shows -56dBc spurious-free dynamic range (SFDR) relative (Figure 6b). typical operating conditions PRFIN -25dBm, IIP3 0.5dBm, conversion gain 8.4dB. LO-to-IF leakage other spurious artifacts filtered narrow-bandpass filter, shown Figure MAX2681 Silicon Germanium double-balanced downconverter) achieves this performance with typical currents only 8.7mA.
Figure This Silicon Germanium double-balanced downconverter provides (0.5dBm) IIP3 level 56dBc dynamic range (b). Another Silicon Germanium downconverter mixer (MAX2680) offers different performance specifications. Available miniature 6-pin SOT23 package, consists double-balanced Gilbert-cell mixer with single-ended port connections. Like MAX2681, operates from single +2.7V +5.5V supply, accepts inputs between 400MHz 2500MHz, downconverts outputs between 10MHz 500MHz. Supply current shutdown mode typically less than 0.1µA. input single-ended broadband port whose typical input VSWR (400MHz 2.5GHz) better than 2.0:1.
Silicon Germanium Front-end Input Sensitivity
evaluate front-end sensitivity achievable using MAX2641/MAX2681 SiGe downconverters, consider QPSK modulation with 4MHz signal bandwidth. simplify calculations, assume perfect rectangular input filter. First, (AntNF) must added counteract insertion loss caused antenna switch front-end passive filter. Next, post-LNA filter added eliminate distortion (other than distortion) generated LNA. Consider using filter with attenuation this purpose. 1900MHz, post-LNA filter adds MAX2681's 11.1dB Total filter mixer 11.1dB 13.1dB input needs high because supplied directly very low-level signal from antenna. mixer attenuated gain: Total (1/GLNA)(NFTOTAL 2.054; NFTOTAL (dB) 10log2.126 3.12dB. With QPSK modulation 10-3 BER, minimum required ratio energy noise energy antenna input Eb/No 6.5dB. absolute noise floor +25°C AbsNfl -174dBm 10log(KT), where +300°K 1.38 10-23. filter bandwidth FiltBwth 10log(4MHz) 66dB. Figure front-end sensitivity QPSK modulation with 10-3 estimated Input sensitivity AbsNfl AntNF FiltBwth NFtotal Eb/No -174dBm 66dB 3.12dB 6.5dB -95.38dBm.
Conclusion
When compared with pure bipolar processes, Silicon Germanium (SiGe) provides lower noise figure frequency frequencies exceeding 1.0GHz. also provides lower supply current higher linearity. Maxim demonstrated highlinearity silicon germanium mixer that exhibits typical IIP3 0.5dBm 1900MHz noise figure 11.1dB (SSB) with conversion gain 8.4dB, while drawing only 8.7mA supply current. higher frequency operation permitted Silicon Germanium's higher transition frequency (fT) enables applications through 5GHz. References
Richard Lodge, "Advantages SiGe Front-Ends." Maxim Integrated Products, Theale, United Kingdom. Chris Bowick, Circuit Designs. (Howard Sams, Inc). Solid-State Microwave Amplifier Design. Wiley-Interscience publication, 1981, ISBN 0-471-08971-0.
More Information MAX2247: QuickView Full (PDF) Data Sheet MAX2321: QuickView Full (PDF) Data Sheet Free Samples MAX2323: QuickView Full (PDF) Data Sheet Free Samples MAX2338: QuickView Full (PDF) Data Sheet Free Samples MAX2640: QuickView Full (PDF) Data Sheet Free Samples MAX2642: QuickView Full (PDF) Data Sheet Free Samples MAX2644: QuickView Full (PDF) Data Sheet Free Samples MAX2645: QuickView Full (PDF) Data Sheet Free Samples MAX2648: QuickView Full (PDF) Data Sheet Free Samples MAX2649: QuickView Full (PDF) Data Sheet Free Samples MAX2651: QuickView Full (PDF) Data Sheet Free Samples
MAX2654: QuickView Full (PDF) Data Sheet Free Samples MAX2680: QuickView Full (PDF) Data Sheet Free Samples MAX2683: QuickView Full (PDF) Data Sheet Free Samples MAX3273: QuickView Full (PDF) Data Sheet Free Samples MAX3892: QuickView Full (PDF) Data Sheet Free Samples MAX9987: QuickView Full (PDF) Data Sheet Free Samples MAX9988: QuickView Full (PDF) Data Sheet Free Samples

2000 Silicon Germanium (SiGe) Technology Enhances Radio Front-End

Top Searches for this datasheet

Other recent searches