· Implements entire DVB-T standard

· Optimal performance in an

SFN environment

· Excellent AWGN performance < 18.0db

(64 QAM, 2/3 code rate)

· Active impulse noise filtering

· Operation using single SAW filter in

the IF path

d i g i t a l i n f o t a i n m e n t p r o d u c t s

Single

Chip Solution

for DVB

T Systems

C X 2 2 7 0 2

Conexant's CX22702 is a single-chip coded orthogonal frequency

division multiplex (COFDM) demodulator/decoder solution for

both 2K and 8K digital video broadcast-terrestrial (DVB-T) systems.

Providing exceptional echo performance, the device is ideally

suited to receiving the broadcast signal in countries deploying

single frequency network (SFN) implementations of the DVB-T

system. The cost-effective CX22702 also offers a high level of

integration, along with the ability to sample the incoming signal

at a high or low intermediate frequency (IF).

Along with COFDM demodulators, Conexant also offers interactive

TV decoder products -- the CX2249x family -- to provide low-cost

solutions for the core electronics of platforms deployed in digital

terrestrial TV networks. A system solution for a high-end set-top

box with integrated hard disk drive (HDD) is shown below

in Figure 1.

D i s t i n g u i s h i n g F e a t u r e s

Tuner

CX22702

CX22492

SDRAM

Flash

Modem

HDD

RJ-11

C/RGB

Stereo

DAC

CX22702

Tuner

Figure 1. CX22702/CX22492-based set-top box system.

d i g i t a l i n f o t a i n m e n t p r o d u c t s

Single

Chip Solution

for DVB

T Systems

C X 2 2 7 0 2

Input Signal

The CX22702 can accept an input signal centered at

a high IF of either approximately 36.167 MHz (typical

for 7 MHz or 8 MHz channels) or 44.1 MHz (for a 6

MHz channel). Alternatively, the input signal could be

at a low IF of approximately 4.57 MHz. The input is an

analog signal, which is sampled using the internal 10-

bit analog-to-digital converter (ADC). The device can

meet European requirements for adjacent-channel

performance with a single SAW filter. The CX22702

uses digital filters to remove adjacent channel signals

(e.g., NICAM). The tuner's automatic gain control

(AGC) is controlled via a single or dual sigma-delta

feedback. Only a simple RC filter is required to

generate the analog control voltage.

From IF Input to MPEG Output

The CX22702 performs all the functions required to

produce an MPEG transport stream output from the

IF input. First, it detects impulse interference by

performing a proprietary analysis of the OFDM

waveform and a detector in the AGC. Then the time

domain adapter enables the chip to address 6, 7,

and 8 MHz bandwidth channels as well as adapt to

different IFs, sample timing and frequency offsets. In

addition, the time domain adapter removes adjacent

channel interference and removes the cyclic prefix

prior to the fast fourier transform (FFT). During

channel acquisition, the time domain adapter uses

a set of algorithms that allow frequency, sample

timing, and guard interval lock to be achieved quickly

and reliably before switching to a different set of

algorithms, which provide good tracking

performance. For optimal performance in an

SFN, the position of the FFT window is dynamically

located to the strongest signal present in the

guard interval.

After the FFT, a common phase-error correction is

applied prior to channel estimation and correction.

Scattered and continual pilot carriers are used to

correct channel distortion, fading and phase noise

within the carrier bandwidth. The channel estimate

also provides Channel State Information (CSI), which

passes on to the Viterbi decoder, where it improves

performance by identifying bits from data carriers

that have undergone severe fading. Additional

proprietary error-correction techniques improve

further upon the performance. CSI can also mask

bits from data carriers that are particularly affected

by co-channel analog interference (e.g., PAL/SECAM).

The CX22702 uses proprietary memory-efficient

algorithms to produce the channel estimate.

By default, the CX22702 initially determines all

transmission parameters (including 2K/8K

transmission mode and guard interval) from the

received signal. These parameters are stored and

used to reduce the time needed for subsequent

channel acquisitions.

The CX22702 can interface directly to all Conexant TV

decoder devices and other commonly available MPEG transport

demultiplexer chips, as well as directly to a DVB common

interface. The data rate is smoothed to remove gaps introduced

by the COFDM guard interval and variation in processing time

within the forward-error correction (FEC) circuitry. This allows

a stable clock reference to be extracted from the transport

stream more quickly, further reducing the overall time before

the viewer sees a picture.

Applications

Figures 3 shows a possible application of the CX22702 using a

conventional tuner architecture and first IF sampling, where an

input signal centered on 36.167 +/ 0.2 MHz is sampled directly.

This method greatly reduces the component count in the tuner,

allowing a mixer and oscillator to be replaced by an amplifier,

which provides the required input level for the ADC. Only one

SAW filter is required in this application.

What is COFDM?

Coded orthogonal frequency division multiplexing

(COFDM) is the method adopted by the Digital Video

Broadcasting (DVB) Group for digital terrestrial broadcast-

ing. (Here, "terrestrial" refers to land-based, as opposed to

satellite broadcasting). To understand what this acronym

means, let's break it down into its component parts.

Frequency division multiplexing (FDM) refers to the divi-

sion of a communications channel into different frequency

bands. This is a commonly used technique in analog TV

broadcasting, in which different TV stations broadcast on

different frequencies. But in analog TV, the carrier frequen-

cies are spaced 6 or 8 MHz apart; in DVB-T, there are 2,048

carriers (with "2K" mode) or 8,192 carriers (using "8K"

mode) in a given 6, 7 or 8 MHz band. Using conventional

techniques, carriers spaced this close together would

interfere with each other. But because the carriers are

"orthogonal", or non-overlapping, they do not. As a TV

signal travels between the transmitter and the receiver, it

may encounter interference from a variety of sources. In

addition, echoes occur as the signal is reflected from hills,

buildings, trees and moving objects. These echoes interfere

with the signal and cause it to fade. By coding the signal

using powerful error-correction techniques (the "coded" in

COFDM), data in carriers that have been destroyed by

interference can be recovered. Because of these capabilities,

COFDM has proven itself superior to other methods of

digital terrestrial broadcasting.

ADC

Resample

Guard

Detector

Window

Position

2K/8K

FFT

Common

Phase-Error

Correction

Trellis

Decoder

Forward Error Correction

Time Domain Adapter

XTAL

Tuner

Forney

Deinterleaver

Reed

Solomon

Decoder

Channel

Estimator

and Corrector

Inner

Demapper and

Deinterleaver

MPEG
Transport
Stream

Pilot

Locate

AGC

PLL

Serial

Interface

JTAG

Figure 2. CX22702 functional block diagram.

f e a t u r e s a n d s p e c i f i c a t i o n s

· Implements complete DVB-T

(ETS 300 744) standard

· DTG, EACEM and NorDig compliant

· 2K and 8K transmission modes

· Optimized for SFN environments

· Dynamic FFT window positioning

· Active impulse noise filtering

· Input signal can be sampled at high

or low IF

· Meets European requirements using

single SAW filter

· AWGN performance <18.0dB

(64 QAM, 2/3 code rate)

· Excellent CCI PAL performance

· Differential or single-ended integrated

10-bit ADC

· Single or Dual

AGC feedback

to tuner

· Four GPIO/

DAC pins

· Internal digital AFC loop (no feedback

to tuner)

· Internal digital clock recovery loop

(fixed frequency input, no need
for VCXO)

· Channel estimation and correction

· Common phase-error correction

· Fast automatic channel-acquisition

time

· Maintains and uses channel state

information (CSI)

· Serial (I

C compatible) host interface

· Can achieve automatic lock from

initial frequency offsets of up
to 200 kHz

· 6, 7 and 8 MHz channel support

· Serial or parallel MPEG transport

stream output suitable for direct
connection to transport demux chips
(CX22490 TV decoder range)

· Minimal host software required

· JTAG boundary scan

· Low power consumption: < 1.0W

· 100-pin MQFP

Because many standard tuners have an IF output at

about 4.57 MHz (32/7 MHz), the CX22702 can also sample

a signal centered on this frequency. Selection is made

using either a pin on the device (first IF) or a register.

In both cases, adjacent channel interference at the same

level as the COFDM signal is removed by digital filtering

inside the CX22702.

www.conexant.com

General Information:

U.S. and Canada: (800) 854-8099

International: (949) 483-6996

Headquarters Newport Beach

4311 Jamboree Rd, P.O. Box C

Newport Beach, CA 92660-3095

Order# 101557A

01-0194

Conexant and the Conexant logo are trademarks

of Conexant Systems, Inc. Other trademarks are

owned by their respective owners. Although Conexant

strives for accuracy in all its publications, this material

may contain errors or omissions and is subject to

change without notice.

THIS MATERIAL IS PROVIDED AS IS

AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES,

INCLUDING MERCHANTABILITY, FITNESS FOR A PARTICULAR

PURPOSE AND NON-INFRINGEMENT.

Conexant shall not be

liable for any special, indirect, incidental or consequential

damages as a result of its use.

PLL

MPEG
TS

20.48 MHz

ADC

CX22702

SCI

SDI

SDO

SCO

Delayed AGC

SAW(s)

36.16 MHz

Figure 3. CX22702 possible application (first IF sampling).

Figure 4. CX22702 pin diagram.

Product Features

Part Number CX22702