~ Common Emitter Amplifier Noise Calculator ~

Calculates the root mean square Noise Voltage VN(rms) at the output of a single stage Common Emitter CE amplifier ~ It does not take into account flicker noise and assumes: Perfect resistive loads ~ A modern silicon transistor with bias components not producing only Johnson noise ~ The transistor gain is uniform within the measurment bandwidth defined

Under Construction and online testing

Boltzmann Constant — k
 J/K ( joules/kelvin )
Charge on a single Electron — q
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
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
Device Temperature — T
˚C ( calculation uses ˚K )
Measurement Noise Bandwidth — Bn
Calculated results using the values entered above
Optimum Collector Current — IC(opt)
µA = β/√1 + β  • VT/(rbb + RS + RE)
Optimum Source Resistance — RS(opt)
Noise Figure — NF
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
Ω =  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
nVrms = √4 k T Bn RS  •Gv    nV/√Hz
Noise at Collector due to rbb — VNrbb
nVrms = √4 k T Bn rbb  •Gv    nV/√Hz
Noise at Collector due to RE — VNRE
nVrms = √4 k T Bn RE  •Gv    nV/√Hz
Noise at Collector due to RC — VNRC
nVrms = √4 k T Bn RC            nV/√Hz
Noise at collector due to IB — VNIB
nVrms = √2 q IB B (RE + rbb + RS‖R) •Gv
Noise at collector due to IC — VNIC
nVrms = √2 q IBn  (R– (re + RE)/α)
Total Noise V at Collector — VNtot
Signal   VS — SNR
= 20 log (GVVS/VNtot) dB = S/N     (SNRout)
Maximum SNR due to RS & RE
= 20 log (VS/√4 k T Bn (RS +RE)  )  dB
Maximum SNR due to RS alone
= 20 log (VS/√4 k T Bn RS)   dB     (SNRin)
Noise Figure NF
= 20 log (SNRout / SNRin)  dB
Using model with 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
Ω = 2 β re
Optimum Source Resistance — RS(opt)
Optimum collector current — IC(opt)
µA = β/√1 + β  • VT/(rbb + RS + RE)


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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