Chipset for building Spread Spectrum devices.

Chipsets for building Spread Spectrum devices.

Chipsets for building Spread Spectrum devices

Broadband data transmission systems, or Spread Spectrum, produced by various foreign companies differ from each other primarily in the method and speed of data transmission, type of modulation, transmission range, service capabilities, etc. This review examines chipsets for such systems in terms of their application and modulation type

More than 20 companies are engaged in the development and production of chip sets for Spread Spectrum devices.

The range of application of the chipsets is quite wide. Depending on this, Spread Spectrum devices can be divided into three categories:

• radio modems for building wireless local area networks;

• office radio telephones (radio handsets);

• various low-speed devices for telemetry, security alarms, etc.

This classification should include CDMA code division multiple access systems and GPS global positioning systems, but consideration of their element base is beyond the scope of this review.

When describing the sets of microcircuits used, the authors do not claim to provide a complete review, since the manufacturers of the final equipment, for obvious reasons, do not advertise the components used in their devices. Information from some microcircuit manufacturers is difficult to access even now, in the age of the Internet.

Let's start with the STEL2000A chip, developed by Stanford Telecom and now manufactured under license by Zilog under the trade name Z87200. The chip is a programmable direct-sequence spread-spectrum transceiver. The Z87200 supports noise-like code lengths from 2 to 64 chips per bit over a wide range of data rates and spread-spectrum parameters. The maximum speed of the transceiver is 2 Mbps.

The Z87200 is available in two versions (25 and 40 MHz) and performs all the digital processing required to encode and distribute transmitted data and receive and decode it. The transceiver uses differentially encoded BPSK and QPSK modulations, and the receiver section can also handle differentially encoded pi/4 QPSK.

Z87200 is used in some modems from Aironet Wireless Communications. In addition, Zilog cooperates with Utilicom Inc., which produces radio frequency sections compatible with Z87200. The cost of Z87200 in Russia is approximately $25.

A kit for working with FHSS technology is offered by Mitel. The beginning of development and the first samples of the kit are among the achievements of GEC Plessey Semiconductors, which was subsequently acquired by Mitel. Mitel carried out further development of the project independently. The new set of chips consists of three devices:

• WL102B — noise-like controller;

• WL600C — radio frequency chip;

• WL800 — frequency synthesizer.

These chips belong to the third generation of the DE6000 GEC family from Plessey Semiconductors and are collectively called DE6038. Currently, the entire kit is available for less than $25 (for 1000 pieces).

Let's take a closer look at this kit.

WL102B is a CMOS PLC microcontroller with an internal 8051 architecture and external flash memory, which performs the entire procedure for converting PCMCIA interface information symbols into a frequency-hopping signal. The maximum information speed is 2 Mbit/s.

The WL600C is a 2.4-2.5 GHz radio frequency transceiver operating at 2.7-3.6 V. It includes a low-noise amplifier, a mixer with filtering of unwanted spectral components, an intermediate frequency (IF) limiter, a quadrature demodulator, a power amplifier with a control circuit, and an RSSI circuit in the receiver. Two-level FSK modulation is used.

The WL800 is a low-power frequency synthesizer operating at 2.7-3.6 V with a maximum frequency of 2.5 GHz and programmable via a classic 3-wire bus. Its special features include a built-in parasitic modulation suppression circuit.

A faster Spread Spectrum kit with the trade name PRISM™ is offered by Harris Semiconductor. The kit consists of the HFA3860 SPS processor, the HFA3724 quadrature modulator-demodulator, the HFA3524 dual-frequency synthesizer, the HFA3624 receiver and transmitter mixer unit, the HFA3424 low-noise amplifier, and the HFA3925 antenna switch with the transmitter power amplifier. The kit is interesting because Harris Semiconductor offers both parts of the project — the processor and the radio frequency. By the way, the company produces a variety of radio frequency path microcircuits, which allows choosing the most optimal solutions depending on their application.

The HFA3860 DSSS processor contains all the functions required for full-duplex or half-duplex operation at a speed of II Mbit/s. The DSSS processor includes two ADCs for analog 1- and Q-inputs. The type of modulation used is differential BPSK and QPSK, as well as MVOK. A special feature of the processor is the function of monitoring the input signal level (via the RSSI circuit), which allows more accurately determining the presence of a useful signal, avoiding conflicts and thereby increasing the network performance as a whole.

The processor is available in a 48-pin TQFP package and can operate in a temperature range from -45 to +85°C.

The rest of the chips in the kit are built classically and do not require a detailed description.

Zilog offers two chips for the Spread Spectrum cordless telephone: the Z87000 controller and the Z87010 audio encoder/decoder. The Z87000 is a Frequency Hopping transceiver/controller designed specifically for 900 MHz cordless telephones. The Z87000 contains a 16-bit digital signal processor (DSP) and a controller to control the RF section. This transceiver uses FSK modulation and time division multiplexing.

The transceiver is available in two versions, designed for use in the temperature range from -20 to +70 C:

• Z87000 — with a supply voltage of 5 V;

• Z87LOO — with a supply voltage of 3 V.

The Z87010 is a 16-bit DSP processor designed to encode voice into a digital signal and then transmit it to the Z87000 processor, as well as for the reverse procedure of converting the digital signal coming from the Z87000.

The finished radiotelephone, both a wearable handset and a base station, should consist of three parts: the Z87000 and Z87010 described above, and a 900 MHz radio frequency section. The latter was created as a result of close cooperation between Zilog and Analog Devices in the form of the AD6190 single-crystal transceiver. It contains all the necessary components, namely:

— low-noise amplifier;

— receiver mixer;

— transmitter mixer;

— transmitter power preamplifier;

— VCO;

— frequency divider;

— limiting amplifier with RSSI circuit;

— voltage stabilizer.

The AD6190 transceiver is specifically designed to interface with the Zilog kit, but can also operate independently as the RF section of a cordless telephone or Spread Spectrum radio modem.

A similar kit for building a cordless telephone in the 900 MHz range was offered in 1998 by AMD. Taking into account the requirements of customers of the final equipment, AMD developed a kit that, with a minimum set of chips, has great flexibility in design. The kit consists of a distributed spectrum DSSS transceiver AT79 C440 radio frequency transceiver AT79 RF440.

The At79C440 controller is a high-tech microcircuit that supports the telephone protocol and performs data formatting, sound processing, and radio frequency transceiver control. Its core is an 8-bit microcontroller compatible with the 8051 family. In addition, the controller has a number of service functions that have become quite common for modern equipment: low battery indication, the ability to switch to low power consumption modes, and others.

Am79RF440 combines all the functions necessary for receiving and transmitting signals in the 902-928 MHz range, using GMSK (Gaussian frequency modulation) as modulation.

Serial production of the kit was scheduled for August 1998. The cost of At79C440 and Am79RF440 (per 100 thousand pieces) is $ 5.95 and $ 3.95, respectively.

Micron Communications, Inc. offers the MSEM256X105G, a microchip designed for remote access systems. The microchip is housed in a 20-pin SOIC package and is a complete transceiver based on DSSS technology.

The principle of its operation is interesting: the transmitter signal is emitted at a frequency of 2.44175 GHz (using amplitude-pulse modulation — ASK), and the receiver input receives a signal at a second carrier frequency of 596.1 kHz, modulated by differential phase-pulse modulation (DPSK). The code length is unchanged and is 31 chips. With a supply voltage of 3 or 5 V, the average current consumption is only 5 mA. The range of such a transceiver is small — 15 feet, the sensitivity of the receiving device is 17 dBm, the transmitter power is not specified. The maximum information rate is 189.3 kbps.

The device is designed specifically for identifying moving objects, for example, when a vehicle passes through a checkpoint. Along with the microcircuit, the manufacturer offers a base station, a micro antenna, and its own physical interaction protocol — Micro Stamp Engine™, and guarantees at least 4 billion user units of a separate system.

Another method of distributed spectrum — Frequency Hopping — is the basis of the chip of the Norwegian company Gran Jansen AS. The GJRF400 chip is also a fully finished transceiver, performing all digital processing of data symbols, their conversion into a noise-like signal, and then into a radio frequency signal in the range of 300-500 MHz. The type of modulation used is FSK.

The microcircuit has a transmitter output power of 5 mW, a receiver sensitivity of 110 dBm, a maximum information rate of 19,200 bits/s; with a supply voltage of 3 V, the consumed current is about 40 mA. It is produced in a 44-pin TQFP package and can operate in a temperature range from -40 to + 85 ° C. The cost of GJRF400 is about $ 13 (for 100 pieces).

The microcircuit is applicable in wireless local area networks, remote access devices, alarm systems and object security.

In addition to those described above, the following companies produce microcircuits for Spread Spectrum technology: Alfa Inc., The American Microsystems Inc., Atmel, Axxon, Cylink, Diablo Research Corporation, Digital Ocean, FreeWave Technologies, Intellon, Motorola, OKI Semiconductor, Proxim, Pulse Engineering, Rockwell WCD, Eucent Technologies, Texas Instruments, Mitsubishi, Samsung, Sony and others.

The most famous companies producing microcircuits for the radio frequency part are Hewlett Packard, Motorola, Philips, RF Micro Devices, TriQuint Semiconductor and others.

It should be noted that the tendency of companies manufacturing such microcircuits is to increasingly integrate the components on a single crystal. However, modern technology so far allows only the simplest systems with a limited set of functions, low speed, etc. to be combined on a single crystal. The matter is complicated by the fact that the harmonic components of the signal, arising during digital processing, often do not get along well with the radio frequency part, which also has enough problems with today's requirements for the spectrum frequency. However, in the near future we should expect the appearance of not sets of chips, but individual microcircuits that perform the described functions with the speeds required by modern standards.