ADC误差与RF性能的关系.pdf

Dynamic Range  Digital receivers for cellular communications require the highest performance from analog-to-digital converters (ADCs) and their supporting cast of RF components[39].  The signal chain must be sensitive enough to capture low-level signals, while providing enough linearity to handle high-level interfering signals (blockers). That is, its dynamic range ought to be high enough. Dynamic Range  Thus, we need digital variable-gain amplifiers (DVGAs) to achieve required gain adjustment.  For low level signal, DVGAs provide high gain to demodulate successfully.  For high level signal, DVGAs provide low gain to demodulate successfully without saturating.  The eventual target is that both low level and high level signal can have the constant power level at baseband chip input. Dynamic Range  For instance, there are three levels Pin : -117 dBm, -19 dBm and -66 dBm.  Pin = -117 dBm, gain = 100 dB  Pin = -19 dBm, gain = 0 dB  Pin = -66 dBm, gain = 45 dB  Eventually, all the three level signals have -20 dBm level at baseband chip input. AGC  In receiver applications, the lower level desired signal is digitized alone or in the presence of an unwanted signal(s) that can be significantly larger in amplitude[39].  Thus, stringent noise and distortion requirements are placed on the ADC  The converters noise figure(NF) is determined by comparing its total noise power to the thermal noise floor. For small analog input signals, the thermal + quantization noise power dominate the ADC‘s noise floor, which is used to approximate the ADCs effective NF[39]. AGC  In general, the ADC often doesn’t have sufficient dynamic range to meet both the NF requirements (receiver sensitivity ) and maximum blocker requirement