A fully silicon monolithic integrated 868/915 MHz FSK/FM/ASK transmitter chip

Abstract

Applications in the new European short range devices (SRDs) band at 868 to 870 MHz are demanding appropriate solutions for low-power transmitters and receivers to build up economic wireless communication links. In the USA, industrial-scientific-medical (ISM) applications can be used in an appropriate band centered around 915 MHz. Transmitter systems for SRDs can be distinguished either from their type of modulation or from the way the modulation is generated. In the first category, we can mainly differentiate between amplitude and frequency or phase modulation (all can be analog or digital), while the second category might be essentially divided into SAW-based and PLL-based solutions. The SAW-versus-PLL aspect has been evaluated in detail elsewhere [Laute, 1999]. This paper deals with a PLL-based, fully integrated silicon monolithic transmitter chip. The first part of this paper outlines some design and implementation issues of the presented radiofrequency integrated circuit (RFIC) transmitter. The RFIC TH7108 from Thesys is housed in a 16-pin shrink small-outline package (SSOP16) and manufactured in a 0.8 /spl mu/m BiCMOS process, featuring a maximum transition frequency of about 14 GHz. The whole chip contains all modules that are required for a modern low power transmitter. Among them are a PLL synthesizer with crystal reference, a voltage-controlled oscillator (VCO), a power amplifier (PA) and some mode-control logic circuitry. The RFIC allows four different modes of operation: whole TX active, whole TX shut down, external clock only and TX only. The external-clock feature can be used to drive a microcontroller. Frequency-shift keying (FSK) is generated by pulling the crystal by an internal MOS switch. Analog frequency modulation (FM) can be achieved by using one external varactor diode that pulls the crystal accordingly. Amplitude-shift keying (ASK) is realized by switching the RPIC's PA on and off. The second part of the paper shows some measurement results that present the actual performance of the transmitter chip. Important parameters such as power consumption, RF output power, frequency tolerance, FSK/FM and ASK feasibility, temperature characteristic and reliability are reported.