Emitter Followerl Noise Factor Calculator


	Calculates the root mean square value of the Noise Voltage V_N(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 R_S 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 so r_bb and r_e are internal ~ The output resistance r_o 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 — R_B		Ω ( Base bias total resistance )
Emitter Resistor —R_E		Ω
Follower Load Resistor — R_L		Ω ( affects input resistance R_in )
Source Resistor — R_S		Ω
Internal output Resistance — r_o		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 )
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 alone		dB = 20 log (V_S/√4 k T B_nR_S ) (SNR_in)
Noise Figure — NF		dB = SNR_in–SNR_out
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 ‖ R_L ‖ r_o ) ]
Amplifier output impedance — R_o		Ω = (R_E ‖ r_o) ‖ [ (R_S ‖ R_B+ r_bb')/(1 + β) + r_e ]
Voltage Gain — A_v		V/V= (R_E ‖ R_L ‖ r_o )/(r_e+ R_E ‖ R_L ‖ r_o )
Amplifier Voltage Gain — G_v		V/V= A_VR_in/(R_S+ R_in)
Noise due to R_S‖ R_B— V_NRS		nV_rms= √4 k T B_nR_S‖R_B• A_v nV/√Hz
Noise due to r_bb — V_Nrbb'		nV_rms = √4 k T B_nr_bb'• A_v nV/√Hz
Noise due to R_L‖ R_o — V_NRo		nV_rms = √4 k T B_nR_L‖ R_o nV/√Hz
Noise due to I_B through r_e— V_NIB		nV_rms = √2 q I_BB_n • (R_S‖ R_B+ r_bb' – r_e)• A_v
Noise due to I_C through r_e— V_NIC		nV_rms = √2 q I_CB_n • (R_E ‖ R_L ‖ r_o ‖ r_e)
Total Noise V at Output — V_Ntot		µV_rms = √V²_NRS+ V²_Nrbb'+ V²_NRo+ V²_NIB+ V²_NIC
Click here for other calculators 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

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

~ Common Collector Amplifier ~ Emitter Follower Noise Factor Calculator ~