Asynchronous spread spectrum communication for a micro-miniature transponder: Implementation and test results

While the field of wireless communication has developed dramatically over the past several decades, there are several notable applications of wireless technologies which impose constraints on power-consumption and form-factor that are not compatible with commercial technologies such as 802.1 la,b,g or Bluetooth. These applications include implantable devices and remote monitoring devices. Such devices are better suited to transponder technology which is more power-efficient and can sustain data rates acceptable for these applications. Using a well-defined set of functional needs and system restrictions, we have developed an ultra-compact and ultra-low-powered transponder which contains spread spectrum (SS) logic for wireless communications. The transponder chip was designed and built in the Jazz BiCMOS SiGe technology. The device is activated via a pure tone and emits a SS response which is modulated over the carrier with binary phase shift keying (BPSK). The SS signal is a Gold Code generated from two 9-bit m-sequence generators. One of the m-sequences is seeded with a fixed value while the other 9-bit register is pinned out and can be a fixed ID or a bus to transmit data from a microcontroller. The data is received and decoded by a standard PC with a high-speed acquisition board. In order to support multiple devices at various distances, asynchronous decoding is applied. When active, the device draws less than 35 mW of power (@ 3.0V). Assuming a duty cycle of less than 1%, the device can be powered for several days using a very small coin battery. The device has been tested in the laboratory; natural environment testing is underway.