RF MicroelectronicsLECTURE -2 : NOISE

BY: AHMED SAKR.

AHMEDSAKR01@GMAIL.COM

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.

γ 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) = 𝑃𝑠𝑖𝑔𝑛𝑎𝑙

𝑃𝑛𝑜𝑖𝑠𝑒

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 :𝑡ℎ𝑒 𝑚𝑎𝑥𝑖𝑚𝑢𝑚 𝑑𝑒𝑠𝑖𝑟𝑒𝑑 𝑖𝑛𝑝𝑢𝑡 𝑙𝑒𝑣𝑒𝑙 𝑎 𝑟𝑒𝑐𝑒𝑖𝑣𝑒𝑟 𝑐𝑎𝑛 𝑡𝑜𝑙𝑜𝑟𝑎𝑡𝑒

𝑡ℎ𝑒 𝑚𝑖𝑛𝑖𝑚𝑢𝑚 𝑖𝑛𝑝𝑢𝑡 𝑙𝑒𝑣𝑒𝑙 𝑖𝑡 𝑐𝑎𝑛 𝑑𝑒𝑡𝑒𝑐𝑡 (𝑆𝑒𝑛𝑠𝑖𝑡𝑖𝑣𝑖𝑡𝑦)

Sensitivity & dynamic range

Dynamic range:𝑡ℎ𝑒 𝑚𝑎𝑥𝑖𝑚𝑢𝑚 𝑑𝑒𝑠𝑖𝑟𝑒𝑑 𝑖𝑛𝑝𝑢𝑡 𝑙𝑒𝑣𝑒𝑙 𝑎 𝑟𝑒𝑐𝑒𝑖𝑣𝑒𝑟 𝑐𝑎𝑛 𝑡𝑜𝑙𝑜𝑟𝑎𝑡𝑒

𝑡ℎ𝑒 𝑚𝑖𝑛𝑖𝑚𝑢𝑚 𝑖𝑛𝑝𝑢𝑡 𝑙𝑒𝑣𝑒𝑙 𝑖𝑡 𝑐𝑎𝑛 𝑑𝑒𝑡𝑒𝑐𝑡 (𝑆𝑒𝑛𝑠𝑖𝑡𝑖𝑣𝑖𝑡𝑦)

SFDR (spurious-free dynamic range): 𝑀𝑎𝑥𝑖𝑚𝑢𝑚 𝑖𝑛𝑝𝑢𝑡 𝑙𝑒𝑣𝑒𝑙 𝑖𝑛 𝑡𝑤𝑜−𝑡𝑜𝑛𝑒 𝑡𝑒𝑠𝑡 𝑤𝑖𝑡ℎ 𝐈𝐌 𝐥𝐞𝐯𝐞𝐥≤𝐧𝐨𝐢𝐬𝐞 𝐟𝐥𝐨𝐨𝐫

(𝑆𝑒𝑛𝑠𝑖𝑡𝑖𝑣𝑖𝑡𝑦)

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?