Dual Digital BTSC Encoder

with Integrated DAC

AD71028

Rev. 0

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FEATURES

2 complete independent BTSC encoders

Pilot tone generator

Includes subcarrier modulation

Typical 23 dB to 27 dB separation, 16 dB minimum

Signal bandwidth of 14 kHz

Dialog enhancement function for playing wide dynamic

range video sources over built-in TV speakers

Includes L-R dual-band compressor

SPI® port for control of modes and effects

Differential output for optimum performance

DAC performance: 92 dB dynamic range, –92 dB THD+N

Output level control for setting aural carrier deviation

Flexible serial data port with right-justified, left-justified,

48-lead LQFP plastic package

APPLICATIONS

Digital set-top box BTSC encoder

PRODUCT OVERVIEW

The AD71028 dual digital BTSC encoder provides two complete

digital BTSC encoder channels, including the pilot-tone

generation and subcarrier mixing functions. Two built-in high

performance DACs are provided to output the BTSC baseband

composite signal. The output of the AD71028 can be connected

with minimal external circuitry to the input of a 4.5 MHz aural

FM modulator.

In addition to the BTSC encoders, the AD71028 also includes a

stereo image enhancement function, Phat Stereo, to increase the

sense of spaciousness available from closely spaced TV

loudspeakers. A dialog enhancement algorithm is also included

to solve the problem of playing wide dynamic range sources

over limited-performance TV speakers and amplifiers. An

extensive SPI port allows click-free parameter updates.

The AD71028 also includes ADI’s patented multibit Σ-∆ DAC

architecture. This architecture provides 92 dB SNR and THD+N

of –92 dB.

FUNCTIONAL BLOCK DIAGRAM

SERIAL

INPUT A

SERIAL

INPUT B

SPI I/O

GROUP

SPI PORT

PLL DIVIDERS

PLL DIVIDERS

SERIAL

INPUT

CLOCK

DOUBLER

CLOCK

DOUBLER

SERIAL

INPUT

CONTROL REGISTERS

PARAMETER RAM

BTSC

ENCODER

CORE A

BTSC

ENCODER

CORE B

BTSC

ENCODED

OUTPUT A

BTSC

ENCODED

OUTPUT B

ANALOG

BIAS

CLOCK

SIGNAL

GROUP

DAC

DAC

BIAS

3

3

4

AD71028

Figure 1. Functional Block Diagram