~ Common Emitter Amplifier Noise Factor Calculator ~

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
 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
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
=  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 B •(rbb + RS ‖ R) •Av
Noise at collector due to IC — VNIC
µVrms = √2 q IBn  •(R– (re + RE))
Total Noise V at Collector — VNtot
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)
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

Valve Audio Articles QUAD Hi Fi QUAD Modifications and information Component Colour Codes Valve data Sheets QUAD Hi-Fi Buy Beer Button

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