Ultrawide bandwidth (UWB) signals allow large amounts of data to be sent very rapidly at very low power. The UWB signals have their energy spread over a very large frequency band, which significantly reduces the interference on any particular lesser frequency bandwidth.
In order for a UWB transceiver to function, it must generate very wide bandwidth signals at a very high frequency. In one proposed implementation of a UWB transceiver, signals up to nearly 10 GHz must be generated. However, many ways of generating appropriate UWB signals at such high frequencies introduce undesirable harmonics into the signals, which in turn can cause spikes (often referred to as spectral lines) in the power spectral density of the transmitted signal. This can cause problems in the operation of UWB devices since under current FCC regulations the transmit power for UWB devices is limited according to the power spectral density (PSD) of the transmitted signal.
The FCC will not allow any portion of the power spectral density of a UWB signal to rise above the limits it imposes. As a result, if a UWB signal includes a spike in its power spectral density, the total transmission power of the UWB signal must be reduced until that spike falls below the FCC's power limits. This scenario can significantly reduce the total signal power of the transmitted signal. Thus, any spectral lines (i.e., spikes in the power spectral density) in a signal transmitted by a UWB device can reduce the effectiveness of that device. It is therefore very important that the power spectral density of the signal output by a transceiver be strictly controlled, and be as smooth and flat as possible.
Accordingly, it would be desirable to reduce the magnitude of any spikes in the power spectral density of any UWB signal generated by a UWB transceiver, since even order distortion will create spectral lines at harmonics of the chip rate (i.e., at the chipping frequency) when using BPSK and QPSK signalling. This reduction can be achieved by generating and using balanced (i.e., differential) signals.
It is also generally desirable to minimize the size and weight of a UWB device. This is true whether the device is portable or is intended to remain stationary. One generally accepted way to reduce the size of a transceiver is to share a single antenna with both a transmitter portion of a transceiver and a receiver portion of a transceiver, eliminating the need for repeating the antenna circuitry for the transmitter and receiver.
In a conventional embodiment that shares an antenna, a transmit/receive (T/R) switch is often used to switch the connections of a single antenna between a transmit circuit and a receive circuit. Thus, during a transmit operation the receive circuit will be isolated from the antenna by the T/R switch, and during a receive operation the transmit circuit will be isolated from the antenna by the T/R switch.
However, although this does generally reduce the overall circuitry in the device, this conventional design requires the inclusion of a T/R switch, which itself adds to the size and complexity of the device.
It would therefore be desirable to provide a wireless transceiver that eliminates the use of a T/R switch, but also minimizes the presence of spectral lines in any resulting transmission.