~ Common Emitter Amplifier Noise Calculator ~


	Calculates the root mean square value of the Noise Voltages V_N(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 (B_n)defined The circled nodes B C and E represent the external connections of the transistor so r_bb and r_e are internal ~ output resistance r_o 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 — R_B		Ω ( Base bias total resistance )
Collector Resistor — R_C		Ω ( load resistor )
Emitter Resistor —R_E		Ω ( undecoupled emitter resistor )
Source Resistor — R_S		Ω
Intrinsic Base Resistance — r_bb		Ω ( resistance of the base material )
Transistor d.c. current gain —β		( also h_FE or 'beta' in some texts )
Collector Current — I_C		mA
Device Temperature — T		˚C ( calculation uses ˚K )
Measurement Noise Bandwidth — B_n		Hz
Calculated results using the values entered above
Signal V_S — SNR		dB = 20 log (G_VV_S/V_Ntot) (SNR_out)
Maximum SNR due to R_S & R_E		dB = 20 log (V_S/√4 k T B_n(R_S+R_E) )
Maximum SNR due to R_S alone		dB = 20 log (V_S/√4 k T B_nR_S) (SNR_in)
Noise Figure NF		dB = SNR_out–SNR_in
Emitter Internal Resistance — r_e		Ω = V_T/I_CV_T= kT/q = mV
Common base current gain —α		= I_C/(I_C + I_B) I_B = I_C/β = µA
Amplifier input impedance — R_in		kΩ = R_B ‖ (r_bb+ (1 + β) (r_e+ R_E))
Voltage Gain — A_v		V/V= α R_C/(r_e+ R_E)
Amplifier Voltage Gain — G_v		V/V= A_VR_in/(R_S+ R_in) = dB
Noise at Collector due to R_S — V_NRS		µV_rms = √4 k T B_nR_S •G_v nV/√Hz
Noise at Collector due to r_bb — V_Nrbb		µV_rms = √4 k T B_nr_bb •G_v nV/√Hz
Noise at Collector due to R_E — V_NRE		µV_rms = √4 k T B_nR_E •A_v nV/√Hz
Noise at Collector due to R_C — V_NRC		µV_rms = √4 k T B_nR_C nV/√Hz
Noise at collector due to I_B — V_NIB		µV_rms = √2 q I_BB_n (r_bb + R_S‖R_B) •G_v
Noise at collector due to I_C — V_NIC		µV_rms = √2 q I_CB_n (R_C– (r_e+ R_E))
Total Noise V at Collector — V_Ntot		µV_rms = √V_NRS²+V_Nrbb²+V_NRE²+V_NRC²+V_NIB²+V_NIC²

Transistor only noise sources referred to input as series and parallel noise resistances R_NV and R_NI
Noise Resistor in series at Base — R_NV		Ω = r_bb + r_e/2
Noise Resistor Base to Emitter — R_NI		Ω = 2 βr_e
Optimum Source Resistance — R_S(opt)		Ω = √R_NV R_NI
Optimum Collector Current — I_C(opt)		mA = β/√1 + β • V_T/(r_bb+ R_S+ R_E)

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"