Presentation on theme: "Common-Collector Amplifier Section 13.1-13.4. Topics Emitter Follower as a power amplifier Push and Pull Output Stage."— Presentation transcript:
Common-Collector Amplifier Section
Topics Emitter Follower as a power amplifier Push and Pull Output Stage
Design Guideline Specs: Av, rsp, v_re gm=Av/(1-Av)/rsp Calculate IC from gm. Determine re from IC and V_RE Calculate VBE. Calculate VB. Calculate IB from IC. Assume that I1=40 IB Calculate R2 from VB. Calcualte R1
V in, m =1 mV V in,pp =2 mVV out,pp =1.47 mV Av(ADS)=0.735 Av(matlab)=0.783
Large Signal Behavior of Common-Collector Amplifier The output does not track the input during the negative swing.
V in, m =1.71 V V BE
Push-Pull Stage Q1 pushes current into RL. Q1 pulls current from RL. Q1 and Q2 are off. Assume that VCC is +5V and VEE is -5V.
Vout versus Vin
V out Versus V in
Vout Versus Vin Crossover Distortion
Improved Push-Pull Stage Q1 and Q2 can not be on at the same time! Keep Q1 and Q2 on V1=Vout+VBE1 V2=Vout-|VBE2| V1-V2=VBE1+|VBE2|=VB
Implementation of VB Add I1 to provide current For D1 and D2.
Current flowing through the Source
Improved Push-Pull Stage Use Q4 to drive the base of Q2
Voltage Gain Full circuit
Voltage Gain from Vin to VN Full circuit To compute VN/Vin, Calculate RN and multiply RN by gm4.
Voltage Gain from N to Out Full circuitGeneral formula: RL/(1/gm+RL)
Small Signal Model of BJT Transistors (NPN)(PNP)
Sanity Check Intuition: gm1=gm2, rpi1=rpi2 Vout/VN=(1+2gm rpi/2)/(rpi/2/RL+1+2gm rpi/2) =(1+beta)/(rpi/2/RL+1+beta) ~=1/(rpi/2/RL/beta+1) =RL/(/(2gm)+RL) Compare Vout /Vn to the generic formula: RL/(1/gm+RL) we see that this formula makes sense!
Sanity Check! R S is transformed to a smaller output resistance.
Gain Calculated Using Matlab
Change R to change Gain. Tweak R to change gm and the gain at the expense of burning more power.