差分放大器之滤波器设计

1、Benefits of Differential Signal ProcessingThe Benefits Become Apparent when Trying to get the Most Speed and/or Resolutionout of a DesignoonoAvoid Grounding/Return Noise ProblemsBetter Distortion/Dynamic Range For thesame Amplitude Differential Signal the Outputs do not Swing as Close to the RailLow

2、er Distortion especially the 2ndsAnalog Signals in High-performance Systems Startand End DifferentialAlmost Always the Signal Source from the Real World is DifferentialHigh-speed ADCs Have Differential InputsWhy Differential Signal Processing isnot More CommonnDifferential Signals are Commonly used

3、Today for ADC and Line DrivingnDifferential Signaling is not Generally Considered for Other Uses Because:oDiscrete Differential Designs can Be Difficult to ImplementSome Applications cannot Tolerate the Higher Cost oNot Many Differential ICs are AvailableTransformers must be UsednAs Speeds and Resol

4、ution Increase the Benefits of Differential Signaling BecomeMore NecessaryHigh-speed AmpsAD8131/2/8Differential Input/OutputMore About the VOCM PinnVOCM Pin separates our diff amps from other diff ampconfigurationsooCreates Best Available Balance High FrequenciesCan be used with AC signal forModulat

5、ion as well as DC Reference VoltagesFrom Ground Referenced Signals (+/-5V supplies) to Single +5V Supply Signals forADCsBetter Distortion in signal chain for +/-5V, than +5VConnect to the ADC reference orany other reference voltagenEasy Level Shift oooAD8131/2/8 vs. Dual Op AmpConfigurationsnCompare

6、d to Dual Op Amp Configuration for Differential Driving:o2 Op Amps, G = +1 and G = -1Output Dynamics are Different at High Frequencies Poor output balance; EMIemissionsooNo Easy Way to Change Common Mode Output Level Distortion Products areAdditiveAD8131/2/8 even harmonics are Nulled by the Common M

7、ode Feedback and OddHarmonics are low by design11Differential Filter CharacterizationnLow Pass, High pass and band-pass active filterswere designed, built and testedoAs shown in the following slides, theoretical and actual resultsclosely agree.nAD8138 needs Small resistor values (10-47 Ohms) in seri

8、es with the feedbackcircuitry to prevent oscillation at approximately 300 MHz.AD8132 does not Require a small resistorFeedback capacitance greater than a fewpFmay result in high frequency de-stabilizationof the AD8132/8.nnDifferential Input to Single-ended Out Amps AD8129/30AD8129/30 vs. Op Amp Conf

9、igurationsnCompared to Single Op Amp DifferentialAmp Configuration for ReceiveroPoor CMRRUnbalanced Input ImpedancesRequires resistor matching for good CMRRnCompared to 3 Op Amp ReceiveroLots of parts and Design TimeoExtra Amps in Signal path lowers BWFor Use with High-speed ConvertersDiff amps to H

10、elp Reduce Clock JitternSome ADCs have Differential Clock Inputs toMinimize Ground Noise Effects on JitteroGround Noise is only one source of jitter which decreases the performance of thefastest ADCsnAs Discussed before, With Differential Signals the Ground Noise becomes CommonModeoAD8131/2/8 can be

11、 used to send the clock signal from its source into the ADCIsolating Analog and Digital GroundsMinimizing Radiated EMIooFor Driving and ReceivingHigh-speed SignalsFast FETsThe NEW Standard for JFET AmplifiersnVery Easy to UsenNegligible Ibiasand I noisenR-R outputnWide supply rangenLow Supply CurrentnLow PriceFast FETsLow-Cost High-Speed AD8033/4nAD8033/4o75MHz Bandwidtho80V/s Slew Rateo3.2mA/Amp Typical Supply