Presentation on theme: "Noise. Resistor Thermal Noise Example Vnr1sqr=2.3288 x 10 -19 Vnr3sqr=7.7625 x 10- 20 Vnoutsqr=3.1050 x10 -19."— Presentation transcript:
Resistor Thermal Noise
Example Vnr1sqr= x Vnr3sqr= x Vnoutsqr= x10 -19
Analytical Versus Simulation
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Noise Spectrum Shaping by a Low Pass Filter As R increases, 4kTR increases, but the bandwidth decreases. Therefore, the bandwidth is constant. Pn,out can only be decreased by increasing C.
Alternative Representation of Resistor Thermal Noise
MOSFETS (Typically 2/3, not to be confused with body effect coefficient)
Noise Voltage Generated Per Device gm/IDgm(mS)gm/gdsVn(nV/sqrt(Hz))Gamma VDS=0.6 I1=100 uA
Flicker Noise Model The flicker noise is modeled as a voltage source in series with the gate: The trap-and-release phenomenon associated with the dangling bond occurs at low frequencies more often. Device area can be increased to decrease noise due to flicker noise.
Corner Frequency Definition: the frequency at which the thermal noise equals the flicker noise.
Corner Frequency (f co )
f co as a function of length
Representation of Noise in Circuits Output noise Input noise – Voltage noise source – Current noise source
Problem of Output Noise Output noise depends on the gain of the amplifier, for example.
Input-Referred Noise Voltage Problem: only valid for when source impedance is low.
Input Voltage Calculation
Calculation of Input-Referred Noise Low source impedance High source impedance
Input Current More significant at High frequencies!
Noise in Single Stage Amplifier Equivalent CS Stages CS CG SF Cascode Differential Pairs
Equivalent CS Stages
Common Source Amplifier The transconductance of M1 must be maximized in order to minimize input-referred noise.
Input Referred Thermal Noise Voltage M2 acts as the current source. The gm of M2 should be minimized. M1 acts as the amplifier. The gm of M1 should be maximized.