RF basic parameter

Chengdu RuiyueXin

Email: ryx@cdryx-tech. com

website: http://www. cdryx-tech

Wireless = data communication on air It’s a 0-wire and infinite-wires link !

Communication channel = air, space, ether, copper i.e. Interface air-conductor = antenna

Maxwell Laws explain and predict all electromagnetic (and therefore electronic) phenomena

Main Mission: put information on a carrier

Carrier :

Frequency ω (= 2πf): bands Amplitude A : energy, distance

Phase φ: synchro

Information signal :

Analogue, Digital Data, bit rate, DDS Bandwith

Modulated carrier (carrier+info) :

Modulation: AM, ASK, FSK, PSK Spread Spectrum

Noise, interference

Important RF parameters

• Power supply, temperature ranges

• Power consumption

Fin Any RF Fout

function

Fosc

Vcc

• Integration (BOM), cost

• Size

• Frequency ranges

• Gain

• Noise Factor, Figure (F, NF)

• IIP3, OIP3, CP-1dB

• Phase Noise

• Leakage (Isolation, Rejection)

Linearity performance : IP3, P1dB specifications

RFin

RFout

f1, f2 f1, f2, f1+f2, f1+2f2, 2f1,2f2

2f1+f2, 2f1-f2, 2f2-f1, 3f1

Rfout = H(jw) . RFin

IIP3 of

+32.5dBm

IIP3

MAX2044

Transfer function: Non-linearities cause dangerous harmonics when RFin not single (band) – Intercept point order n or IPn!

IPn measured by 2 close input frequencies.

Most dangerous = IP3 (because products fall in same original frequency bands!

Noise Factor & Figure

Noise Factor:

Noise Figure:

Friis’ Formula:

Phase Noise in dBc/Hz

Central frequency

Offset

frequency

Phase Noise : scope view

Offset

Understanding IP3 spec

Transfer function:

Non-linearities cause dangerous

f1, f2 f1, f2, f1+f2, f1+2f2, 2f1,2f2

2f1+f2, 2f1-f2, 2f2-f1, 3f1 Rfout = H(jw) . RFin

Any RF

function

(LNA, mixer,

PA, filter )

RFout

RFin

harmonics when RFin not single (band) – Intercept point order n or IPn!

IPn measured by 2 close input frequencies.

Most dangerous = IP3 (because products fall in same original frequency bands!

Understanding 1dB compression point

Any RF

function

(LNA, mixer,

PA, filter )

RFout

RFin

Conversion loss (normally constant with RFpower), starts to increase 1dB_C is when additional 1dB reached

Low Noise Amplifier (LNA)

Noise Figure NF = 10 log(SNR_in / SNR_out)dB

L.N.A

Good LNA = High NF !!! i.e. 1 to 2 dB

SNR-out

SNR-in

Main Role of the LNA:

Amplify the very very weak signal

from antenna into a suitable signal

form able to be handled by rest of the electronic (filters, downcoverter,

demodulator, etc ) WITHOUT adding to much noise

Other Charateristics for a good LNA

• Noise Figure (limit adding noise to signal)

• IP3 (« linearity » performance, distorsion = noise)

• Gain (i.e. > 30 dB but usually degrades NF)

• Frequency band (i.e. larger bandwith = more noise)

• Current consumption

• Operating Voltage

• Operating temperature (i.e. temperature add noise)

• Integration (i.e. LNA must be close to antenna)

Mixers or frequency converter

Main role of Mixer is to make frequency translation (heterodyning)

Frequency shift (conversion) is required because:

• Suitable propagation in space (i.e. Antenna size, Attenuation, noise, perturbators, allowed standards…)

• Suitable processing in Electronics and compatibilities (i.e. Crystal, SAW filters )

• Frequency change is made via non-linear operation (multiplication)

• Outputs are various combinations of input frequencies: Fout = +/- nF1 +/-mF2

• Up-Converter : Output frequency > Input Frequency

• Down-Converter : Output Frequency < Input Frequency

Mixing Operations