第三章 射频微电子学 之调制解调基础_图文

1、射频微电子学 AgendaAdvantagesand Trade-offs Digital Signal CharacteristicsBandwidth EfficiencyFor a given bandwidth, a digital signal can send moreinformation than an analog signal.Digital signals can be highly compressed.QualityDigital signals can contain information that allows datadamaged in transmissi

2、on to be repaired at the receiver.Digital signals deliver high quality services. Analog vs. Digital Signal ResponseDigital A n a l o g Increasing number of impairmentsSignalQuality goodmuch better still greatbeginning to getcustomercomplaints good until itcrashescustomerrebellion AgendaDigital Modul

3、ation BasicsTransmitting Information(Analog or DigitalModify a Signal"Modulate"Detect the Modifications"Demodulate"Any reliably detectable change in signal characteristics can carry informationModulation.where the information resides V= A(t sin2f(t+(tAM, PulseFM PMV= A(t sin(t Ag

4、endaI/Q Transmittersand Receivers Analog to Digital ConversionSampling:Taking “snapshots”of the analog signal fast enough to preserve its frequency response.f s > 2 fc(Nyquist TheoremQuantizing:Turning the samples into amplitude values with enough resolution to preserve the waveform changes.Encod

5、ing:Turning the quantized samples into binary data for storage or transmission. Quantization ErrorThe difference between a digital value and the analog value it represents due to the limitations in the ADC process.The smaller the quantization error, the better the digital signal reproduces the original analog waveform.