| 摘要 |
In a radio transmitter, such as a mobile communications device, a filter is adjusted, based on a power level of a signal for transmission is detected, and/or on a mode of operation of the device. The bandwidth of the filter is adjusted, by controlling a transconductance element in the filter. The filter can therefore be controlled to have characteristics which are suitable for the operating conditions of the device in which the filter is being used, and which give an acceptable switching spectrum for the signals, while also allowing the output power of the power amplifier to ramp up acceptably quickly. For example, the filter can be adjusted depending on the communications standard (e.g. GSM or PCS) under which the device is operating, and depending on the power level of transmitted signals. |
