差分放大器之滤波器设计.doc

Benefits of Differential Signal Processing The Benefits Become Apparent when Trying to get the Most Speed and/or Resolution out of a Design o on oAvoid Grounding/Return Noise ProblemsBetter Distortion/Dynamic Range –For the same Amplitude Differential Signal the Outputs do not Swing as Close to the Rail–Lower Distortion especially the 2ndsAnalog Signals in High-performance Systems Start and End Differential –Almost Always the Signal Source from the Real World is Differential –High-speed ADCs Have Differential Inputs Why Differential Signal Processing is not More Common nDifferential Signals are Commonly used Today for ADC and Line Driving nDifferential Signaling is not Generally Considered for Other Uses Because: oDiscrete Differential Designs can Be Difficult to Implement–Some Applications can not Tolerate the Higher Cost oNot Many Differential ICs are Available –Transformers must be Used nAs Speeds and Resolution Increase the Benefits of Differential Signaling Become More Necessary High-speed AmpsAD8131/2/8Differential Input/Output More About the VOCM PinnVOCM Pin separates our diff amps from other diff amp configurations o oCreates Best Available Balance @ High FrequenciesCan be used with AC signal for Modulation as well as DC Reference Voltages From Ground Referenced Signals (+/-5V supplies) to Single +5V Supply Signals for ADCs Better Distortion in signal chain for +/-5V, than +5VConnect to the ADC reference or any other reference voltagenEasy Level Shift ooo AD8131/2/8 vs. Dual Op Amp Configurations nCompared to Dual Op Amp Configuration for Differential Driving: o2 Op Amps, G = +1 and G = -1 –Output Dynamics are Different at High Frequencies ?Poor output balance; EMI emissions o oNo Easy Way to Change Common Mode Output Level Distortion Products are Additive –AD8131/2/8 even harmonics are Nulled by the Common Mode Feedback and Odd Harmonics are low by design11 Differential Filter CharacterizationnLow Pas