Multi-StandardMulti-Band Receiver Design.THEORY AND RF FRONT END DESIGN. PART-1

Multi-Standard

Multi-Standard transceiver is like a man who can speak multiple languages, it can operate in different communications standards.

For example, the receiver inside the cellular phone in your hand, it can operate over 2G (GSM), 2.5G (EDGE, GPRS), 3G (UMTS) and 4G.

Multi-standard RF front-end

GSM

EDGE

GPRS

LTEUMT

S WiMAX

Digital processin

g Subsyste

m

Data

Multi-Band

There are standards that operate on different frequency band for the same standard, for example: WLAN IEEE 802.11 standard:

802.11a : from 5.15 to 5.35 GHz in/out Door. from 5.725 to 5.85 GHz outdoor. 802.11b/g: 2.4-2.4835-GHz.

WiMAX IEEE 802.16e: 2.5 GHz band & 3.5 GHz band.

For a Multi-Standard transceiver it should operate over different frequency bands with different bandwidths depending on each standard it supports.

Multi-Standard transceiver:

A Multi-Band/Multi-Standard transceiver (TRX) is a radio front-end that can be operated in a number of frequency bands. The frequency bands can be changed easily without modifying the hardware.[Ref.1]

The modern upgrades of the Multi-standard transceiver are:

Software-Defined-Radio, which is a multi-standard radio with reconfigurable digital processing using embedded systems or computers.

And cognitive radio, which is a SDR with the ability of sensing the surrounding spectrum to use the unused frequency bands for better spectrum efficiency.

Receiver Architecture.

Receiver ArchitectureSuper-Heterodyne Receiver

The signal of interest is down-converted to an intermediate-frequency, then re-down-converted to DC (Zero IF) or very low IF.

Receiver ArchitectureSuper-Heterodyne ReceiverImage problem.

if an interferer locates in frequency equals to fRF – 2fIF for LO < fRF or at fRF+ 2 fIF for LO> fRF, that interferer will be down-converted to the IF band of interest, interrupting the desired signal and reducing the selectivity and sensitivity of the system.

Receiver ArchitectureSuper-Heterodyne ReceiverImage problem- low side injection.

Desired Signal

LO signal

Interfere@ fRF-2fLO

Down-converted

signal Up-converted

signal

Interferer’s image appears at fIF

Receiver ArchitectureSuper-Heterodyne Receiver

Advantages Immunity to LO leakage and interferer leakage. Negligible mismatch between I and Q channels because I&Q split is done after

the second mixer where the IF is low enough. Pitfalls: Requires more external components, not suitable for SoC. More complicated in design. Image problem while image rejection is not easily achievable.

Receiver ArchitectureDirect conversion Receiver (Zero-IF receiver)

A simple structure where the signal is directly down-converted to zero or very low IF.

Simple LNA and channel selection filters are replaced with LPF.

Receiver ArchitectureDirect conversion Receiver (Zero-IF receiver)

Advantages: Solve the problem of image. LNA doesn’t have to drive a 50 Ohms load since there are no Image

Rejection BPF. Suitable for full integration. Suitable for multi-standard if programmable LO frequency and LPF are

used.

Receiver ArchitectureDirect conversion Receiver (Zero-IF receiver)

Disadvantages: DC offset [added DC voltage to the signal causing distortion and losses]. Even order distortion. Flicker noise. LO leakage. Self-mixing[adds undesired signal at zero IF].

Receiver ArchitectureQuasi-IF Receiver

To solve the problems of Direct-conversion- receivers. The signal is down-converted to a very low IF. Image problem is re-introduced!

Receiver ArchitectureDigital-IF Receivers

The signal is down-converted to intermediate frequency IF. Then it is converted to digital using ADC. The second down-converting and demodulation are performed

in digital domain effectively.

Receiver ArchitectureDigital-IF Receiversdesign issues:

Adjacent interferers or blockers are directly added to the ADC’s input, so a wide dynamic range is required in the ADC to prevent ADC saturation by

high power level blockers and to sense the very low level signal. To relax the image problem, IF cannot be very low. If the signal’s BW is comparable to the IF, Low Pass ADCs are used instead of

band pass. To relax the requirements, subsampling is used.

Subsampling ReceiverTHEORY AND DESIGN

Subsampling: Subsampling is the process of sampling a signal with a frequency lower

than twice the highest signal frequency, but higher than two times the signal bandwidth, the signal is down-converted by subsampling instead of mixing.

Subsampling:selecting subsampling frequency

Where: fs : Subsampling frequency. BW : signal bandwidth. fc : carrier frequency. m : number of replicas between 0Hz and (fc-BW/2).

Subsampling:selecting subsampling frequency

An appropriate value for fs is

Here, choosing an odd value for m ensures that a replica of the signal is produced at fs/4, which results in a larger subsampling frequency bandwidthand relaxes the filtering requirements after the sampling-and- hold stage.While using even value for m will generate the low-frequency aliasing of the signal at 3fs/4 and degrade the signal quality.

Subsampling:Architecture

Because carrier, subsampling, and intermediate frequencies

are all related, there is a trade-off between bandwidth and subsampling frequency.

Subsampling:

The effect of selected subsampling frequency, which results in the presence of 2nd order effects.

Specifications.

Specifications Specific requirements:

Programmable gain. Programmable tuning over bands of

interest. Programmable bandwidth. Resources reuse whenever

applicable. Multi-band Frequency synthesizer.

General requirements:High dynamic range.High sensitivity.High selectivity.

Over all supported standards!

Input

Output

Specifications

The specifications of MS radio should meet the requirements of all the supported standards in the common parts, as the UWB LNA, Mixers, …etc.

Depending on the specifications and blocking profiles, the system requirements are extracted by using the equations in the next slide.

Specifications Equations BW: Bandwidth. C/N: Carrier to Noise Ratio. PN: Phase Noise. NF: noise figure. SIR: Signal-to-Interferer ratio. Safety margin is considered after calculating the system requirements.

GSMGlobal System for Mobile communications.REQUIREMENTS.

GSM

GSM frequency plan

Global system for mobile communications.

Was developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation (2G) digital cellular networks used by mobile phones, first deployed in Finland in July 1991.

As of 2014 it has become the default global standard for mobile communications - with over 90% market share, operating in over 219 countries and territories. [Wikipedia]

Specifications

GSMintermodulation test

The intermodulation test specifies a Gaussian minimum shift keying (GMSK) signal 3 dB above the sensitivity level has to be detectable in presence of a 49-dBm continuous wave and a 49-dBm GMSK modulated interferer placed at 800- and 1600-kHz frequency offset from the desired signal, respectively.

Therefore, the required third-order input intercept point (IIP3) is -18 dBm.

-99 dBmDesired signal @fo

-49 dBm tone @fo±0.8 MHz

-49dBm GMSK signal @fo±1.6 MHz

GSMAM suppression test

GMSK is used as modulation in GSM. This modulation form has a DC peak making it vulnerable to DC offset problems.[Ref]

This test was introduced in order to avoid receiver desensitization in presence of a GMSK pulse jammer, as produced by the on/off-switching signal on another carrier.

a -99-dBm desired signal has to be correctly demodulated in presence of a -31-dBm AM modulated interferer.

IIP2> 2PAM – noise floor. IIP2 > +49 dBm. Challenging.

GSMReceiver Requirements

Parameter ValueSensitivity -102 dBm, with BER<10-4

Max Noise figure 9dB @200 kHz BWAntenna referred noise floor -111 dBmIIP3 -18 dBmIIP2 +49 dBmLO tuning range 60 MHzLO Phase Noise (PN) -141 dBc/Hz.

Problems:• Sensitive to the 1/f noise of the CMOS in the zero-IF receiver.• Image effect in the low-IF receiver. • Very high IIP2.

UMTSUniversal Mobile Telecommunications System.

UMTS Universal Mobile Telecommunications System. A third generation mobile cellular system for networks based on

the GSM standard. UMTS uses wideband code division multiple access (W-CDMA) radio access

technology to offer greater spectral efficiency and bandwidth to mobile network operators.

It uses WCDMA for better spectrum using efficiency. The WCDMA coded signal modulates the carrier using QPSK. The code used in the receiver should be well synchronized with the one used in

coding the signal in transmitter.

UMTSfrequency plan In the user equipment side:

TX : from 1920 to 1980 MHz. RX: from 2110 to 2170 MHz. Signal BW: 8 - 384 kHz. Code BW: 3.84 MHz, FIXED. Channel spacing: 5 MHz. TX-RX spacing: 135 MHz. Data rates:

384 kbps outdoor. Up to 2 Mbps indoor.

UMTSOut-of-Band Intermodulation test The transmitter leakage is responsible for

intermodulation products due to third-order nonlinearity, together with an out-of-band continuous wave interferer.

In the worst case, these two interfering signals are placed, respectively, 135 and 67.5 MHz apart from the receive band.

Since the desired signal power is 3 dB above the sensitivity level in presence of out-of-band interferers and the noise level is -99 dBm, the upper limit for the third-order intermodulation product is set at -99 dBm as well. The required out-of-band IIP3 , evaluated at the receiver input, is given by -4.6 dBm.

-99dBmDesired signal @fo

-40 dBm tone @fo±67.5 MHz

-49dBm GMSK signal @fo±135 MHz

UMTSIn-band Intermodulation test

-46 dBm continuous wave and a -46 dBm WCDMA-modulated interfering signal, placed 10 and 20 MHz apart from the desired signal carrier frequency.

The resulting antenna referred in-band IIP3 requirement is -17 dBm.

Notice that, while the in-band requirement demands high linearity throughout the receiver (including the baseband circuits), the out-of-band specification mainly affects the RF front-end because the interferers can be strongly attenuated at the down-converter output, at least in the zero-IF or low-IF architectures.

-99 dBmDesired signal @fo

-46 dBm tone @fo±10 MHz

-46dBm GMSK signal @fo±20 MHz

UMTSReceiver Requirements

From the standard specifications and blocking profile the receiver requirements are calculated as following

Parameter ValueSensitivity -117Max Noise figure 6.15 dBAntenna referred noise floor -99 dBmIIP3 -4.6 dBmIIP2 +46 dBmLO tuning range 60 MHzLO Phase Noise (PN) -150 dBc/Hz. &135MHz offset.

Bluetooth

ISM BAND SHORT RANGE COMMUNICATION TECHNIQUE.

Bluetooth A low-cost, low-power communication protocol designed for short-

range radio connectivity between electronic devices, invented by 1999. Operates on the ISM (Industrial-Scientific-Medical) 2.4 GHz frequency

band which is license-free worldwide. Using FHSS (Frequency-Hopping-Spread-Spectrum) has the advantage

of interferer immunity. Channel BW: 1-MHz. Modulation scheme: Binary Frequency Shift Keying (BFSK) with

Gaussians shaping filter. The Gaussian-shaped BFSK signal has most of its energy in

approximately 200 kHz (3-dB bandwidth) so that a zero-IF CMOS solution would require some effort to address 1/f noise.

Low-IF receiver is selected because it allows very good sensitivity with low power consumption. Commercially, a 1 or 2 -MHz IF is chosen.

BluetoothReceiver Specifications

Low IF receiver

Analog Demodulato

r

Tx maximum power: 0, 4, 20 –dBm for a range of 10-50 m.

Receiver sensitivity: -70 dBm. BFSK allows the use of limiters and

analog demodulators which are more power efficient.

21- dB SNR for 10-3 maximum BER. 23-dB Noise Figure. VCO tunable range 2.4-2.48 GHz. -15 dBm IIP3 with -39 dBm interferers

and -64 dBm received signal. Low-IF receiver architecture is selected

because the 1/f noise problem,

Wireless LANHIGH-RATE WIRELESS NETWORK CONNECTIVITY.

WLANIEEE 802.11 Standard

Formalized in 1999, to allow high-rate wireless communication between personal computers and workstations, avoiding the use of expensive and bulky wires.

IEEE 802.11 had a maximum 2Mbps using FHSS or DSSS in the 2.4 GHz ISM band.

IEEE 802.11a has up to 54 Mbps in the 5GHz band. IEEE 802.11b extended the throughput of IEEE 802.11 to reach

11Mbps. IEEE 802.11g supports up to 54Mbps in the 2.4 GHz ISM band,

supporting the IEEE 802.11b standard.

WLANIEEE 802.11a-1999

Operates on the UNII ( Universal Networking information infrastructure): UNII-1&2 : From 5.15GHz –to- 5.35GHz: for indoor and outdoor

use. UNII-3 : From 5.725GHz –to- 5.85 GHz for outdoor use only.

Each UNII band provides four 16.6MHz OFDM modulated non-overlapping channels.

OFDM [orthogonal frequency division multiplexing] is used for its high spectral efficiency and reduced multipath inter-symbol-interference.

IEEE 802.11aReceiver Requirements

The most stringent receiver requirements are set in the 54Mbps mode.

Parameter ValueFrequency band 5.15GHz –to- 5.35GHz :

in/outdoor.5.725GHz –to- 5.85 GHz : outdoor.

Channel BW 16.6MHzSensitivity -65Max Noise figure 7.5 dBSignal-to-receiver-noise ratio 28 dB1-dB compression point -20 dBmLO tuning range 20-40 MHzLO Phase Noise (PN) -102 dBc/Hz. &1MHz offset.

IEEE 802.11aReceiver Requirements

OFDM modulation has a hard requirements to achieve. Receiver should has low NF less than other standards at more than twice the operating frequency.

The baseband/IF chain is also challenging because of the large bandwidth and high SNR.

For zero-IF receiver, it is required to have low 1/f noise corner frequency and HP filtering frequency to avoid signal corruption. While the training time for DC cancellation is much smaller than 802.11b, only 8μSec. Many commercial 802.11a receivers are using zero-IF architecture.

For low-IF receivers, DC offset cancellation is not a huge problem because the edges of the channel don’t carry information, and image suppression required is lower than zero-IF. The main disadvantage is the higher power consumption.

WLANIEEE 802.11b-1999

Operates on the ISM licence-free 2.4: 2.4835 GHz band.

Channel bandwidth: 14MHz. Two operation modes: 5-11 Mbps The most challenging is the 11Mbps

mode, whose spectral efficiency is 0.78 bps/Hz.

IEEE 802.11bLinearity parameters

-30 dBm continuous wave interferer or a -35 dBm adjacent signal interferer, placed 30 and 25 MHz apart from the desired signal carrier frequency.

The CW interferer sets the receiver 1-dB compression point to -26 dBm taking a 4dB safety margin.

It also sets the LO Phase noise to -103 dBc/Hz at 1-MHz offset with a VCO tuning range of 80 MHz.

-70 dBmDesired signal @fo

-35 dBm adjacent

signal @fo±25

MHz

-30dBm tone@fo±3

0 MHz

IEEE 802.11bReceiver Requirements

The most stringent receiver requirements are set in the 54Mbps mode. for IEEE 802.11b can be implemented by the zero IF receiver, where the dc

offset problem is solved using HP filter and 1/f noise is integrated over the band of interest.

Parameter ValueFrequency band 2.4-2.4835 GHzChannel bandwidth 14 MHzSensitivity -76 dBmMax Noise figure 14.8 dBSignal-to-noise ratio 11.5 dB1-dB compression point -26 dBmLO tuning range 80 MHzLO Phase Noise (PN) -103 dBc/Hz. &1MHz offset.

WLANIEEE 802.11g-2003

IEEE 802.11g is an improvement to the IEEE 802.11 specification that extended throughput to up to 54 Mbit/s using the same 2.4 GHz band as 802.11b.

802.11g hardware is fully backwards compatible with 802.11b hardware In an 802.11g network, the presence of a legacy 802.11b participant

will significantly reduce the speed of the overall 802.11g network.  802.11g suffers from the same interference as 802.11b in the already

crowded 2.4 GHz range. 802.11g receivers have to meet the most critical requirements set by

802.11b and 802.11a. However, the 1-dB compression point is set to -10dBm in the receiver

low-gain mode.

IEEE 802.11b/gchannels.

To prevent interference, there are only three non-overlapping usable channels in the U.S. and other countries with similar regulations (channels 1, 6, 11, with 25 MHz separation), and four in Europe (channels 1, 5, 9, 13, with only 20 MHz separation)

Zero-IF receiver architecture is efficiently used for IEEE 802.11g.

IEEE 802.11n - 2009 Its purpose is to improve network throughput

over the two previous standards—802.11a and 802.11g, with a significant increase in the maximum net data rate from 54 Mbit/s to 600 Mbit/s by using MIMO [Multiple-input Multiple-output].

Channel bandwidth increased from 20 MHz to 40 MHz which, besides using MIMO, increase the transfer rate of the system.

IEEE 802.11n allows up to 4×4:4 MIMO. Data rates up to 600 Mbit/s are achieved only

with the maximum of four spatial streams using one 40 MHz-wide channel.

IEEE 802.11a-b&gSummary

Multi-Standard RF front-end summary: Multi-standard receiver can be

easly implemented by making a transceiver for each standard, but this will increase both the cost and power consumption.

By carefully designed system where sharing of hardware whenever possible, and use of tunable, programmable gain & bandwidth elements are guaranteed, the power consumption and total cost can be minimized.

THE END OF PART-1

References:

“Toward Multistandard Mobile Terminals—Fully Integrated Receivers Requirements and Architectures”, IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 53, NO. 3, MARCH 2005, Massimo Brandolini and others.

Multi-standard radio transceiver architecture and radio frequency front end design, The Ohio state university, Hyung Joon Kim, 2005.

Multi-Standard Mixed-Signal Transceivers for Wireless Communications —A Research Overview, Troels Emil Kolding, Aalborg University, Denmark, December 1996.

MULTI-STANDARD CMOS WIRELESS RECEIVERS: Analysis and Design, Consulting Editor: Mohammed Ismail. Ohio State University.