RF Microelectronics LECTURE -2 : NOISE BY: AHMED SAKR. [email protected] SUPERVISED BY: PROF. HESHAM HAMED DR. MAHMOUD A. ABDELGHANY.
RF MicroelectronicsLECTURE -2 : NOISE
BY: AHMED SAKR.
SUPERVISED BY:
PROF. HESHAM HAMED
DR. MAHMOUD A. ABDELGHANY.
Introduction
Performance limitations
The two main performance
limitations in RF design are noise and
nonlinearity.
Noise is RANDOM, which means that
the instantaneous value of noise can
not be predicted.
Noise is expressed in term of its
average power Pn.
Device Noise
Thermal noise of resistors
Resistors noise is modeled by an ideal resistance
in series with voltage source with Vn2 or in parallel with
a current source of In2.
model should be chosen to simplify calculations.
The polarity of the sources is unimportant but should be same throughout the entire calculations.
Device Noise
Noise of MOSFETsThermal, flicker.
Ξ³ is the Excess noise coefficient. 2/3 for
long channel MOS, >= 2 for short channel
MOSs.
Thermal noise may be modeled by series
voltage source with the gate or parallel
current source between the drain and source.
flicker noise 1/f.
Device Noise
Noise of MOSFETsThermal, flicker.
Flicker noise 1/f. modeled by a
voltage source in series with the gate.
The choice of the lower frequency
of the system should be larger than the
Corner frequency fc.
flicker noise+ nonlinearity+ (time-
variance) = translation of flicker noise
into the band of interest [Mixers, OSC]
(*)K is a process-
dependent constant
Representation of noise in circuits.
Input-referred noise
Noise is modeled by series voltage source & parallel current source.
To calculate Vn2 we short the input port and measure output noise,
To calculate In2 we do the same with input port opened.
Representation of noise in circuits.
Noise figure
SNR (signal-to-noise ratio) = ππ πππππ
πππππ π
NF describes the added noise from the
circuit into the signal.
Sensitivity & dynamic range
Sensitivity is the minimum signal level that a
receiver can detect with acceptable quality.
Noise floor
The total integrated noise of the system
Dynamic range :π‘βπ πππ₯πππ’π πππ ππππ ππππ’π‘ πππ£ππ π ππππππ£ππ πππ π‘ππππππ‘π
π‘βπ ππππππ’π ππππ’π‘ πππ£ππ ππ‘ πππ πππ‘πππ‘ (ππππ ππ‘ππ£ππ‘π¦)
Sensitivity & dynamic range
Dynamic range:π‘βπ πππ₯πππ’π πππ ππππ ππππ’π‘ πππ£ππ π ππππππ£ππ πππ π‘ππππππ‘π
π‘βπ ππππππ’π ππππ’π‘ πππ£ππ ππ‘ πππ πππ‘πππ‘ (ππππ ππ‘ππ£ππ‘π¦)
SFDR (spurious-free dynamic range): πππ₯πππ’π ππππ’π‘ πππ£ππ ππ π‘π€πβπ‘πππ π‘ππ π‘ π€ππ‘β ππ π₯ππ―ππ₯β€π§π¨π’π¬π ππ₯π¨π¨π«
(ππππ ππ‘ππ£ππ‘π¦)
Impedance transformation
Quality Factor
Quality factor Q indicates how close to ideal an energy-storing
device (Inductor, Capacitor) is.
Impedance transformation
Parallel to series conversion
Quality factor Q indicates how close to ideal an energy-storing
device (Inductor, Capacitor) is.
For Q2>>1 (true for a finite frequency range)
Impedance transformation
L sections used for matching
Sometimes the load resistance is needed to become larger or
smaller, that can be achieved by matching networks as following
Scattering parameters.
Scattering parameters.
Input matching
Reverse gain
Output matching
Gain
Any Questions?