| 摘要 |
<p>A circuit tuneable between first and second frequencies, such as LC circuit 30, fig.3, comprises a gain control circuit 33 operable to control the gain (or Q) of the tuned circuit between the first and second frequencies. The gain control circuit 33 comprises a resistor network having at least two resistor lines connectable in parallel, each resistor line comprising one or more resistors (e.g. 401) and a switch (e.g. 407) operable to select or deselect the corresponding resistor line. The switchable resistor network controls the Q of the tuned circuit ("de-Q"). The resistor lines may be binarily weighted, whereby the three-switch circuit of fig.4 can give eight different resistance values (including open circuit). Logic (not shown) may be configured to control the switches so as to minimise the variation in gain of the circuit between the first and second frequencies. The circuit of fig.4 has a fast settling time and provides performance sufficiently good to allow a single tuning circuit to be used in ultra-wideband (UWB) radio receivers across an entire band group.</p> |
