radio-frequency transmission. A radio transceiver is composed of a set of building blocks each of which use a subset of passive and active components. A crystal or possibly in the future a MEMS device produces a frequency reference that is multiplied up and combined with a phase-locked loop to produce a frequency reference that can be changed and stable. On the transmit path a carrier can be produced and information placed on the carrier using a combination of phase, frequency and amplitude modulation. The signal is then amplified and filtered using surface acoustic wave or bulk acoustic resonator filters and then applied to an antenna. In a users device this signal can be in the order of 10 milliwatts dB), 100 milliwatts (+20 dB) or a watt (+30 dB) or more. You will probably remember that one watt is equal to 1 joule (J) of energy per second. On the receive path the received signal will be several orders of magnitude smaller. Table 2.12 shows some levels typically encountered in radio systems. A picowatt is one million millionth of a watt - no wonder we use a logarithmic notation to describe this stuff. Table 2.12 Typical received signal levels Received signal in picowatts24 0.001 0.0001 0.00001 0.000001 24 Conversion tables for dBM and a comprehensive treatment of RF transceiver design can be found in The Mobile Radio Servicing Handbook Belcher, Fitch, Ogley, Varrall, ISBN 0-434 92187-4, first published in 1989 by Heinemann Newnes. Making Telecoms Work To put this in context a modern mobile phone with a GPS receiver is expected to recover a signal below -150 dBm in immediate proximity to a transmit signal of the order of 27 or 28 dB, a dynamic range of nearly 180 dB. This signal has to be recovered and filtered and amplified through a low-noise amplifier without being compromised by oscillator noise or other sources of internal or external interference. Over time there has been a steady improvement in component performance, a topic revisited in more detail in Chapter 5. This includes active device performance, 