Size
Weight
Battery Life
Price
Cost reduction through integrated circuits
Baseband Processor
Advanced RISC Machine (ARM)
Mixed Signal Design
Technology Nodes
Battery Technology

While the battle of systems was raging in America, the battle of devices was raging in Europe. The different mobile phone operators did not differ significantly. Possibly only to the extent of availability and call dropss. And there weren’t any big differences in terms of voice quality, for example.

Differentiators were coming from the actual phones. As already described, car phones were no longer of interest. People wanted handheld devices. As small and as stylish as possible.

Motorola, Ericsson and Nokia had taken the first steps. All other manufacturers of end devices now had to follow.

Trends in development of mobile phones

Four items where important for a mobile phone:

• Size
• Weight
• Standby time and Talk time
• Price

Based on theses items there was a war going on in the 90ties to develop the most attractive devices for the young mobile phone market.

Size

The first target of a portable mobile phone was to be comfortable in the hand and to hold it to your ear for maybe 10 minutes without getting tired. And of course it had to be easy to transport, in a briefcase or handbag. None of the first devices actually met these criteria, but at least they were „transportable“.

Target sizes were defined. If it was to fit comfortably in one hand, a length of 10 – 12 cm was desirable. With a width of 5 cm and a thickness of 2 cm, an ideal volume would be 120 cc. That was a quarter of the first generation devices. At this size it would also fit comfortably in a shirt pocket. The ability to carry a telephone in your shirt pocket has long been a strong selling point. It has been reported that some phone vendors had special shirts with larger pockets to demonstrate how the devices fit better.

Integration was the main way to shrink mobile phones

How to reduce the size? A mobile phone consists on many components. So first these components should become smaller. The main components are the circuit boards with the electronics and the battery. However, the circuit boards can only be made smaller if fewer electronic devices have to be placed on them. So the number of electronic devices need to be reduces and this requires that more and more functionality has to be places on fewer integrated circuits. This means higher integration.

Weight

Weight is crucial when carrying and holding the device. About the weight of a landline telephone receiver would be good. A target value here was 100 – 150 grams. An important element in terms of weight was the battery. Here it is required to find a compromise between the weight and the battery life of the phone. Many suppliers offered batteries with different capacities. So they were able to offer a low weight but only with a low capacity battery. If customers wanted longer runtime, they had to buy a heavier batteries.

When it comes to weight, the battery was initially a key factor.

Otherwise the same applies as for size. When everything gets smaller and higher integrated, it usually gets lighter.

Battery life

There were two elements regarding battery life. The standby time and the talk time. The standby time is the time that a phone can be in stand by and logged into the network. A GSM phone, even if it is just lying around, is not passive. It has to constantly check for an incoming call and it has to check if the network environment for changes and communicate this to the network.

Practically everything is active during talk time. In this case the transmitter is the part that consumes the most energy.

Initially, GSM devices had a standby time of 10-12 hours and a talk time of around an hour. This resulted in customers always carrying 1-2 spare batteries. The standby time could initially be extended by optimizing the processes in the telephone. It’s about switching of everything that isn’t needed at the moment. To do this, it is necessary actually required to design a device in such a way that you really can switch everything off. This is not a given. One trick the manufacturers did, for example, was that they even switched off the main oscillator (13 MHz). Instead, a simple oscillator like the one used in watches was left running to bring up the system back to life when, for example, a paging channel had to be queried. To switch of the VCTXO was significantly saving power.

To achieve long battery life, it was required to switch off everything that was not really needed for the operation.

The same holds for the optimization of talk time. Of course during talk time there is far more activity but TDMA allows also here to switch off elements. As we have learned only one time slot is used for receive and only one time slot is used for transmit. So at least the transceiver is active for only 1/8 of the time. This is especially important for transmit since the power amplifier consumes most power. It is also important to use the lowest power level as possible for transmit to save power.

Another factor for the battery life was of course the general power consumption of every component. When developing new circuits and especially new ICs, particular attention should be paid to power consumption. Significant power savings came primarily from the transition to new semiconductor technology nodes. With each new “node,” the circuits not only became faster and smaller, they also consumed less power.

Price

Perhaps the most important element was the price of the phone. Initially, the prices of GSM telephones were 3,000 DM (Deutsche Mark, 1,500 euros). But after just one year, it was almost impossible to sell a phone for more that 1,000 DM. The target price, where a phone would become a „consumer item“ would was assumed to be around 300 DM. A phone would be on the same level like a radio receiver or a TV set.

The price hat several reasons. Especially the number of components increased also the price. Therefore also in this case higher integration was important. Higher integration means fewer components, smaller and less circuit boards. This was beneficial for production, since less components also means less assembly time in the assembly lines and therefore less production cost.

The fewer components a phone has, the less susceptible it is to failure and increases the yield during production, which is also important for cost.

Also the quantities are important for production cost. It takes a lot of investment to set up a production line to produce a phone. The cost for this setup decreases with the number of phones that are produced on this line. While previously only a few thousand phones of one model were manufactured, now there were 100,000 or more where produced.

Therefore the following targets could be seen for phones in the mid nineties:

	Base line	Target	factor
Size	1000 – 3000 ccm	120 ccm	10
Weight	500 – 2000 g	100 g	10
Standby Time	10 h	48 h	5
Talk Time	1 h	6 h	6
Price	1000 – 2000 DM	300 DM	3 – 7

Cost reduction through integrated circuits

The lion’s share of savings potential lay with semiconductor manufacturers. The manufacturer had to reduce the number of components and reduce power consumption. The reduction of components was mainly achieved through integration.

The Baseband Processor

The following digital functions can be integrated:

• DSP
• Microcontroller
• Timer
• Card reader

Such a chip that integrates the various functions is called the baseband processor. This term comes from the “radio world”. The radio is transmitting in the RF (radio frequency) band. Super Heterodyne receivers generate an intermediate frequency (IF) before it is mixed down to the so-called baseband. The baseband is therefore the actual information carrying signal, which in GSM has a bandwidth of around 200 kHz. This signal is digitized for further processing. This processing is therefore called baseband processing.

Integration onto a chip, an „Application Specific Integrated Circuit“ (ASIC), has so far not been a classic task for a device manufacturer. A special design team is needed to create an ASIC.

The semiconductor manufacturers quickly realized that mobile communications opened up a new line of business in which millions of ICs were needed. They practically couldn’t afford not to play in this market. The following companies therefore started to built baseband solutions.

• Texas Instruments
• Motorola (later Freescale)
• AT&T (later Agere)
• Siemens Halbleiter (later Infineon)
• Philips Semiconductors (later NXP)
• Analog Devices
• VLSI
• LSI

The semiconductor manufacturers worked closely with the end device manufacturers. Motorola, Philips and Siemens had their respective semiconductor branches. Texas Instruments quickly had a strategic alliance with Nokia. Ericsson worked with Philips and VLSI.

Almost all semiconductor companies had their own DSP which they either developed directly for GSM or tailored it for GSM. For example, Motorola had to build a 16 bit version of its famous 56000 DSP, which had a word width of 24 bits, so that it could be used for GSM.

It was more difficult for some manufacturers to find a suitable microcontroller. A standard 8-bit microcontroller was too weak. A controller developed for the computer sector, such as Intel’s 80×86 architecture, was not very suitable and consumed too much power.

Advanced Risc Machine (ARM)

In the late 1980s, Apple was planning a new product. A Personal Digital Assistant (PDA). This was more or less the grandfather of the iPad. On the market this PDA was called the Apple Newton. From the beginning, Apple knew they needed a dedicated controller/processor for this product. This should be very powerful but consume little power. Ultimately, the PDA was intended to become a portable device.

The English company Acorn had a suitable controller that they had developed for their PCs. This had a RISC architecture. RISC stands for Reduced Instruction Set Computer. This means that the processor has a simple and limited instruction set. Typically, only a single function could be executed with one command. At first this seems to be a disadvantage. On the other hand, this architecture makes the processor fast because the instructions can be executed faster. In addition, less power is required.

Apple contacted Acorn and together with the semiconductor company VLSI. They founded Advanced RISC Machine ltd (ARM) in 1990. Apple brought the money, Acorn brought the processor and VLSI brought the semiconductor technology. The first chips that ARM developed went into the Apple Newton.

However, ARM’s business model was not to build and market CPU chips, but to license the architecture to customers. In 1993, Texas Instruments was one of the first users of the ARM, although not yet for the mobile phone market. But TI was confident enough in ARM’s architecture that they suggested Nokia use it. The ARM processor at the time had a 32 bit architecture. This worried Nokia because it would require expensive memory. Otherwise, they were impressed by the performance. ARM reacted promptly and developed a special 16 bit version for the mobile phone market, the ARM 7. Because this was a „reduced ARM“, it was also nicknamed Thumb. Nokia was satisfied and TI licensed the ARM 7. Many manufacturers now also switched to ARM 7 giving up their own processors.

The famous Nokia 8110 was the first GSM phone with an ARM processor in 1996.

Mixed Signal Design

When designing complex systems such as a GSM phone, manufacturers tried to separate digital circuits and analog circuits, i.e. to place them on different ICs. The main reason for this was that digital circuits generate strong disturbing signals that interfere with sensitive analog circuits. For example, an analogue-to-digital converter was always placed on its own chip and only the digital signal was transferred to the DSP.

In the 1990s, however, it was possible to combine analog and digital on one CMOS chip. (CMOS, Complementary metal–oxide–semiconductor is the most common technology for the production of integrated circuits). This led to the highest level of integration of a baseband processor.

The figure above shows an example of a baseband processor, in this case from the company VLSI in 1998 which they called OneC. It includes a DSP with its own memory for data and programs. Plus the converters that connect it to audio and the radio. The ARM 7 (Thumb) serves as the controller with its boot memory and the interfaces to external memory. There are many interface blocks to connect the controller to the outside world or so that the controller can control external components. Furthermore the interfaces to the SIM card, the keyboard and the display. There are also special accesses to the ARM to be able to check a program that is running on it (trace and debug). The only additional things to build a phone would be a radio and external oscillators.

Technology Nodes

The semiconductor industry is and has been in constant change. Every 1-2 years the technology was improved towards smaller structures. This was called Moore’s Law, which states that the number of transistors in an area doubles every two years. This means that the structure size of the circuits halves every two years. One speaks of technology nodes.

At the beginning of the 1990s the structure size was still at 600 nm. In 1996 it was only 250 nm. This had several effects. First of all, it was possible to install more transistors per square millimeter and achieve higher integrations. Since the costs of producing an IC are mainly based on the cost of a silicon disk (wafer), you can get an IC cheaper with each new technology node. In addition, the circuits are faster. For example, a DSP could execute more commands per second with a new technology node. This was primarily known from the PC industry, where CPUs became faster every year in the 1990s. Above all, the operation voltage also changed with the technology.

In 1990 it was still at 3.3 V for a digital circuit. In 1996 the ICs were already operated with 2 – 2.5 V. As the voltage is reduced, the power consumption also drops significantly. This means you get significant electricity savings through integration and by using the latest technology nodes.

Battery technology

Battery technology was particularly important for mobile communications in the 1990s. These had to be rechargeable batteries.

Rechargeable batteries have been around for a long time, especially for the automotive industry and for military technology. Such batteries where the lead batteries, like they were used as car batteries. But these had a crucial disadvantage. They were big and heavy and could leak. So they were not usable for mobile devices.

Nickel cadmium batteries were used for the first portable mobile devices. This was the standard battery technology of the seventies and eighties, for example when it came to replacing standard disposable batteries with rechargeable batteries. However, nickel cadmium was not very efficient and was also toxic. Furthermore, there were so-called memory effects that quickly caused the batteries to lose their capacity if you did not always ensure that the batteries were discharged before recharging them.

At the end of the 1980s, a new battery technology came onto the market, the nickel-metal hydride battery. This was not toxic and had a significantly better energy density than nickel-cadmium batteries. In the 1990s, NiMH batteries were installed everywhere.

However, from the mid-1990s onwards, another battery technology came to market. The lithium-ion battery. This battery had twice the energy density. Furthermore, a lithium-ion battery had a higher voltage (above 3V) compared to the 1-1.2V of NiMH and NiCd. A Sony lithium-ion battery was sold for the first time in 1993 for a camcorder. In 1996 it was installed in a GSM telephone for the first time. It doubled the battery life with the same weight. Until today, that lithium ion battery is the standard.

Technology	Energy density Wh/kg	Voltage V
Lead	30	2
NiCd	40-60	1 – 1,2
NiMH	60 – 110	1 – 1,2
Lithium	120 – 210	3,2 – 3,7