DESIGNING THE ISD33000 SERIES INTO DIGITAL CELLULAR PHONES
Introduction
Cellular phone manufacturers are constantly under pressure to release new models of
phones with compact designs and more user features. This puts tremendous pressure on
their development teams to re-engineer the phone architecture, software development,
hardware development and layout. Time to market with a new product is also crucial
for manufacturers to remain competitive.
An emerging trend in cellular phone handsets is the addition of “voice” features. These
voice features include: 1) the “on-the-fly” recording of telephone conversations, which
eliminates the need for writing down notes and improves driving safety by enabling
hands free usage, 2) recording voice memos, where reminders are left for oneself, and
3) integrating a telephone answering machine, which can screen or capture otherwise
missed calls. The basic function which enables these new features is the ability to reli-
ably record and playback voice messages. To meet the requirements of cellular handset
performance, the solution must be low-power, to conserve battery life, have a small form
factor, to enable a compact design, low-cost to keep the retail pricing down, and repro-
duce high quality sound, to meet the expectations of consumers. Additional factors to
consider are development time and costs, since a quick time-to-market and effective
design investment are critical for new products.
The following design illustrates how a single ISD33000 device can be integrated into a
GSM cellular handset to enable these new “voice” features. With minimal hardware and
software development, this solution provides one to four minutes of high quality, voice
record and playback capability with low-power consumption and minimal board space.
In addition, this implementation of the ISD33000 is easily portable to other analog or
digital cellular, PCS or PHS handsets because it is integrated in a manner which is inde-
pendent of the transmission and processing protocol being utilized.
Integration of an ISD33000 into a GSM Phone
The block diagram of the ISD33000 series voice recorder chip integrated into a typical
GSM digital cellular phone is shown in Figure 1. The GSM architecture is based on a
typical GSM chip-set available from one of the several semiconductor manufacturers in
the U.S.A.