# ~ Common Collector Amplifier ~ Emitter Follower Noise Factor Calculator ~

 This page uses JavaScript Which your browser does not appear to have enabled The following calculator will not function Calculates the root mean square value of the Noise Voltage VN(rms) at the Output of an Emitter follower ~ Are emitter followers noisy when used as pre-amplifiers ? ~ If the output impedance presented to the next stage is lower than RS but the SNR is not affected very much is this an adavantage ? Calculation does not take into account flicker noise and assumes: Perfect resistive loads and a modern silicon transistor with low noise bias and the transistor gain is constant within the measurment bandwidth defined The circled nodes B C and E represent the external connections of the transistor so rbb and re are internal ~ The output resistance ro is included but if not known assume its value is >2MΩ ~ Click here for other calculators Boltzmann Constant — k 1.3806x10-23 J/K ( joules/kelvin ) Charge on a single Electron — q 1.6022x10-19 C ( coulomb or amperes/sec) Base bias Resistor — RB Ω ( Base bias total resistance ) Emitter Resistor —RE Ω Follower Load Resistor — RL Ω ( affects input resistance Rin ) Source Resistor — RS Ω Internal output Resistance — ro Ω Intrinsic Base Resistance — rbb Ω ( resistance of the base material ) Transistor d.c. current gain —β ( also hFE or 'beta' in some texts ) Collector Current — IC mA Device Temperature — T ˚C ( calculation uses ˚K ) Noise Bandwidth — Bn Hz Calculated results using the values entered above Signal   VS — SNR dB = 20 log (GVVS/VNtot)     (SNRout) Maximum SNR due to RS alone dB = 20 log (VS/√4 k T Bn RS  )   (SNRin) Noise Figure — NF dB = SNRin –SNRout Emitter Internal Resistance — re Ω = VT/IC       VT = kT/q = mV Common base current gain —α = IC/(IC + IB)   IB = IC/β = µA Amplifier input impedance — Rin kΩ =  RB ‖ [ (rbb + (1 + β) (re + RE ‖ RL ‖ ro ) ] Amplifier output impedance — Ro Ω = (RE ‖ ro) ‖ [ (RS ‖ RB + rbb)/(1 + β) + re ] Voltage Gain — Av V/V = (RE ‖ RL ‖ ro )/(re + RE ‖ RL ‖ ro ) Amplifier Voltage Gain — Gv V/V = AV Rin /(RS + Rin) Noise due to RS ‖ RB — VNRS nVrms = √4 k T Bn RS‖RB • Av  nV/√Hz Noise due to rbb — VNrbb nVrms = √4 k T Bn rbb • Av       nV/√Hz Noise due to RL ‖ Ro — VNRo nVrms = √4 k T Bn RL ‖ Ro        nV/√Hz Noise due to IB through re— VNIB nVrms = √2 q IB Bn • (RS ‖ RB + rbb – re) • Av Noise due to IC through re — VNIC nVrms = √2 q IC Bn • (RE ‖ RL ‖ ro ‖ re) Total Noise V at Output — VNtot µVrms = √VNRS2 + VNrbb2 + VNRo2 + VNIB2 + VNIC2 Click here for other calculators See these references: The Art of Electronics 3rd edition chapter 8 ~ By Paul Horowitz and Winfield Hill ~ fellow cynics Noise in Transistor Circuits ~ By P. J. Baxandall ~ Wireless World November 1968 ~ often referenced Designing low–noise audio amplifiers ~ By Wilfried Adam ~ Wireless World June 1989 Introduction to low–noise amplifier design ~ By A. Foord ~ Wireless World April 1981 The design of Low-noise audio frequency amplifiers ~ By E. A. Faulkner ~ The Radio and Electronic Engineer July 1968 ~ This article along with the book 'Low-Noise Electronic System Design' By C. D. Motchenbacher and J. A. Connelly should answer most questions about electronic noise

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