| 摘要 |
A variable frequency filter circuit, provided with a low pass filter constituted of a gm amplifier, is a low pass filter circuit in which a micro controller controls a current value converting circuit so as to adjust a reference current of the low pass filter in order to adjust a cut-off frequency. When the variable frequency filter circuit is in an adjusting mode, the variable frequency filter circuit detects a shift in a cut-off frequency of the low pass filter for filtering an actual signal. As to a dynamic change in a power supply voltage, ambient temperature or the like, which cannot be detected in real time, a value of the shift can be worked out in advance and with accuracy via simulation. Therefore, the shift is compensated in accordance with the value stored in a data memory. This requires no need of an arrangement to have a separate reference filter for detecting a shift for compensation of the shift, thereby eliminating an influence the arrangement. Therefore, this suppresses influence due to relative unevenness of circuit elements as to circuit layouts, reduces electrical consumption, and prevents an interference signal from reaching to a received signal.
|
