# ~ Common Collector Amplifier / Emitter Follower Noise Calculator ~

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 and lower case 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 ( resistive part 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 = √V2NRS + V2Nrbb' + V2NRo + V2NIB + V2NIC