# ~ Common Emitter Amplifier 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 Voltages VN(rms) that appear at the OUTPUT of a single stage Common Emitter (CE) amplifier based on the a.c. model opposite The focus is on the amplfier Noise Figure ~ Resuts in nV/√Hz are the respective resistor Johnson noise voltages It does not take into account flicker noise and assumes: Perfect resistive loads and modern silicon transistor with low noise bias and the transistor gain (β) is constant within the measurment bandwidth (Bn) defined The circled nodes B C and E represent the external connections of the transistor so rbb and re are internal ~ output resistance ro is not used here 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 ) Collector Resistor — RC Ω ( load resistor ) Emitter Resistor —RE Ω ( undecoupled emitter resistor ) Source Resistor — RS 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 ) Measurement 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 & RE dB = 20 log (VS/√4 k T Bn (RS +RE)  ) Maximum SNR due to RS alone dB = 20 log (VS/√4 k T Bn RS)    (SNRin) Noise Figure NF dB = SNRin – SNRout Transistor alone maximum NF 10 log (1 + (rbb+ re/2 )/RS + (rbb+ re + RS)2/(2βre RS)) 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)) Voltage Gain — Av V/V = α RC/(re + RE) Amplifier Voltage Gain — Gv V/V = AV Rin /(RS + Rin) = dB Noise at Collector due to RS — VNRS µVrms = √4 k T Bn RS  •Av    nV/√Hz Noise at Collector due to rbb — VNrbb µVrms = √4 k T Bn rbb  •Av    nV/√Hz Noise at Collector due to RE — VNRE µVrms = √4 k T Bn RE  •Av    nV/√Hz Noise at Collector due to RC — VNRC µVrms = √4 k T Bn RC            nV/√Hz Noise at collector due to IB — VNIB µVrms = √2 q IB Bn  •(rbb + RS ‖ RB ) •Av Noise at collector due to IC — VNIC µVrms = √2 q IC Bn  •(RC – (re + RE)) Total Noise V at Collector — VNtot µVrms = √VNRS2+VNrbb2+VNRE2+VNRC2+VNIB2+VNIC2 Transistor only noise sources referred to input as series and parallel noise resistances RNV and RNI Noise Resistor in series at Base — RNV Ω = rbb + re/2 Noise Resistor Base to Emitter — RNI kΩ = 2 β re Optimum Source Resistance — RS(opt) Ω = √RNV RNI Optimum Collector Current — IC(opt) mA = β/√1 + β  • VT/(rbb + RS + RE) Click here for other calculators See these references: The Art of Electronics 3rd edition chapter 8 ~ By Paul Horowitz and Winfield Hill Noise in Transistor Circuits ~ By P. J. Baxandall ~ Wireless World November 1968 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

"Do you work it out one by one ~ Or played in combination"