RF MicroelectronicsCHAPTER- 2: BASIC CONCEPT'S.

BY: AHMED SAKR.

SUPERVISED BY:

PROF. HESHAM HAMED, DR. MAHMOUD A. ABDELGHANY.

Introduction

RF section of Cellphone

RF section of a cellphone

Introduction

Design bottleneck

RF Section is the bottleneck of wireless

communication systems. Because:

- The performance of the RF front end affects the

overall performance of the entire system.- RF design involves many disciplines the designer

should understand.

- There are many trade-offs in RF design.

- Relay on experience even while using design tools.

Trade-offs in RF design

Basic concepts.

Design bottleneck

Nonlinearity

• Harmonic distortion.

• Compression.

• Intermodulation.

• Dynamic nonlinear systems.

Noise

• Noise Spectrum.

• Device Noise.

• Noise in circuits.

Impedance Transformation

• Series- Parallel conversion.

• Matching networks.

• S-Parameters.

Unites in RF

Logarithmic operations review

𝑖𝑓 10𝐴 = 𝐵 , 𝑡ℎ𝑒𝑛 log 𝐵 = 𝐴

log1

𝑥= − log 𝑥

log 10𝑥 = 𝑥log 𝑥𝑎 = 𝑎𝑙𝑜𝑔(𝑥)

log 𝑥𝑦 = log 𝑥 + log 𝑦

log𝑥

𝑦= log 𝑥 − log 𝑦

Unites in RF

Gain

Rin Rout

Vin Vout

𝑽𝒐𝒍𝒕𝒂𝒈𝒆 𝒈𝒂𝒊𝒏 𝑨𝒗 =𝑉𝑜𝑢𝑡

𝑉𝑖𝑛𝑅𝑀𝑆

𝑷𝒐𝒘𝒆𝒓 𝒈𝒂𝒊𝒏 𝑨𝑷 =𝑃𝑜𝑢𝑡

𝑃𝑖𝑛=

𝑉𝑜𝑢𝑡2

𝑅𝑜𝑢𝑡𝑉𝑖𝑛2

𝑅𝑖𝑛

=𝑉𝑜𝑢𝑡2

𝑉𝑖𝑛2×𝑅𝑜𝑢𝑡

𝑅𝑖𝑛= 𝐴𝑣2 ×

𝑅𝑜𝑢𝑡

𝑅𝑖𝑛

𝐢𝐟 𝐑𝐨𝐮𝐭 = 𝐑𝐢𝐧 ⇒ 𝐀𝐏 = 𝐀𝐯𝟐

Unites in RF

Gain (in dB)

𝒅𝑩 𝑨𝒗 = 20log(𝑉𝑜𝑢𝑡

𝑉𝑖𝑛)

𝒅𝑩 𝑨𝑷 = 10 log𝑃𝑜𝑢𝑡

𝑃𝑖𝑛

= 10 log𝑉𝑜𝑢𝑡2

𝑉𝑖𝑛2×𝑅𝑜𝑢𝑡

𝑅𝑖𝑛

𝑠𝑖𝑔𝑛𝑎𝑙 𝑝𝑜𝑤𝑒𝑟|𝑑𝐵 𝑃𝑠 = 10 log𝑃𝑠

1𝑚𝑊→ 𝑖𝑓 𝑅𝑜𝑢𝑡 = 𝑅𝑖𝑛 ⇒ 𝒅𝑩 𝑨𝒑 = 𝒅𝑩(𝑨𝒗)

𝑽𝒐𝒍𝒕𝒂𝒈𝒆 𝒈𝒂𝒊𝒏 𝑨𝒗 =𝑉𝑜𝑢𝑡

𝑉𝑖𝑛𝑅𝑀𝑆

𝑷𝒐𝒘𝒆𝒓 𝒈𝒂𝒊𝒏 𝑨𝑷 =𝑃𝑜𝑢𝑡

𝑃𝑖𝑛=

𝑉𝑜𝑢𝑡2

𝑅𝑜𝑢𝑡𝑉𝑖𝑛2

𝑅𝑖𝑛

=𝑉𝑜𝑢𝑡2

𝑉𝑖𝑛2×𝑅𝑜𝑢𝑡

𝑅𝑖𝑛= 𝐴𝑣2 ×

𝑅𝑜𝑢𝑡

𝑅𝑖𝑛

→ 𝐢𝐟 𝐑𝐨𝐮𝐭 = 𝐑𝐢𝐧 ⇒ 𝐀𝐏 = 𝐀𝐯𝟐

Unites in RF

Voltage gain Vs. power gain

Rin Rout

Vin Vout

We are interested in calculating the output

voltage rather than the output power

when the input and output impedance are

not equal or contain negligible real parts.

Why?

Because the voltage gain is not equal to

the power gain in this case, which is

common in RF design.

Linearity and time variance

LinearityFor a linear system, if:

X1(t) → Y1(t) , X2(t) → Y2(t)

aX1(t) + bX2(t) → aY1(t) + bY2(t)

Otherwise, the system is nonlinear.

Time Variance

For a time invariant system, if:

X(t) → Y(t)

Then : X(t-T)→ Y(t-T)

Otherwise, the system is time variant.What about nonzero initial conditions and

dc offsets? - They are linear too.

Linearity and time variance

Switching system

Nonlinear, time variant Linear, time variant

Linearity and time variance

Nonlinear, time variant

Linearity and time variance

Linear , time variant Vin2 delayed by 45 degree

Memory-less systems [outputs don’t depend on past values of

input(s), opposite to Dynamic systems.]

Memory-less linear systems

y(t) = x(t)

Memory-less nonlinear systems y(t) = 1 x(t) + 2 x2(t) + 3 x3(t) +… n xn(t)

If j=0 for even j, the system is said to

have odd symmetry, when his

response to –x(t) is negative to that to

x(t).

The circuit having this property is

called differential or balanced.

Nonlinearity effects.

y(t) = 1 x(t) + 2 x2(t) + 3 x3(t) +… n xn(t)

DC

component

Total

Gain [compression

@ 1 3 <0]

2nd

harmonic

Suppresse

d for odd

symmetry.

3rd

harmonic

Small

signal

gain

Harmonic distortion.

y(t) = 1 x(t) + 2 x2(t) + 3 x3(t) +… n xn(t)

DC

componentfundamental 2nd

Harmonic

3rd

Harmonic

In many RF designs, the harmonics

distortion is unimportant but should be

tested before they are dismissed, usually

harmonics are filtered, but it is a key

parameter to test the performance of

specific circuits such as Mixers

Common

in

MIXERS

&OSC

Gain compression

y(t) = 1 x(t) + 2 x2(t) + 3 x3(t) +… n xn(t)

DC

component

Total

Gain [compression

@ 1 3 <0]

2nd

harmonic

Suppresse

d for odd

symmetry.

3rd

harmonicSmall

signal

gain

@ 1 3 <0 the gain is compressed as A rises

1 =500

3 =-0.1

Gain compression [1-dB compression point]

@ 1-dB compression point, the gain is

reduced by 10%

Desensitization: when large

interferer [blocker] causes gain

compression while sensing weak

desired signal.

[lowers the SNR]

Cross modulation.

y(t) = 1 x(t) + 2 x2(t) + 3 x3(t) +… n xn(t)

Weak signal + large interferer

large interferer:

Variations in A2 (modulation) affects the

amplitude of the signal (A1) Common

in

AMPLIFIERS

Intermodulation.

Intermodulation

components

Fundamental

components

Intermodulation.

Third order intermodulation products are the most important. If the difference between w1 and

w2 is small they will appear close to the fundamentals, making it hard to design a filter to

discard the effect of them.

This effect is significant in LNA as shown in next figure…

Intermodulation[two-tone test].

Two signals with

small A is chosen to minimize

nonlinearity effect on it

Gain = 1

Fundamental A

IM products A3

Plot in log-log scale,

the intersection is

the third-order

intercept point

IIP3 is beyond the allowable

input range or even higher

than the supply voltage,

because if the input level

reached the AIP3 the gain

drops and higher order IM

products become significant.

Intermodulation[two-tone test].

IIP3 is chosen beyond the allowable

input range or even higher than the

supply voltage, because if the input level reached the AIP3 the gain drops

and higher order IM products

become significant.

AIIP3 is greater than

the 1-dB compression

point with 9.6 dB

IIP3 direct calculation. [two-tone test].

Any Questions?