Filter circuit, and receiver and electronic device using the same filter circuit
View Patent ↗Filter circuit includes Nth-order active filters switching circuit which switches shorting or non-shorting of active filter, and power-supply control circuit which controls such that a power supply of active filter is turned off when switching circuit shorts active filter. A receiver employing filter circuit turns off the power supply of active filter not needed when no interference wave exists within a given range from a desired frequency band. The foregoing structure allows lowering the power consumption of filter circuit.
1. A filter circuit comprising:
an Nth-order active filter;
a switching circuit for switching at least a part of the Nth-order active filter to be shorted or not to be shorted;
a power-supply control circuit for turning off a power supply of at least the part of the Nth-order active filter when the switching circuit shorts at least the part of the Nth-order active filter; and
a passive element control circuit for controlling a constant of a passive element of the Nth-order active filter,
wherein the passive element control circuit switches the passive element of the Nth-order active filter, of which power supply is turned off by the power-supply control circuit, to function as a passive element of the Nth-order active filter of which power supply is turned on.
2. The filter circuit of claim 1 further comprising:
a switch disposed respectively before and after at least a part of the Nth-order active filter; and
a switch coupled in parallel with the switches and at least a part of the Nth-order active filter.
3. The filter circuit of claim 1 , wherein the Nth-order active filter includes a first passive element and a second passive element coupled in parallel with the first passive element,
wherein the passive element control circuit controls a constant of the passive elements depending on an open or a not-open of the second passive element.
4. The filter circuit of claim 1 , wherein the Nth-order active filter includes a first passive element and a second passive element coupled in series to the first passive element,
wherein the passive element control circuit controls a constant of the passive elements depending on a short or a not-short of the second passive element.
5. The filter circuit of claim 1 , wherein the passive element of the Nth-order active filter of which power supply is turned off is disposed adjacently to the passive element of the Nth-order active filter of which power supply is turned on.
6. A filter circuit comprising: an Nth-order active filter;
an Mth-order active filter coupled in parallel with the Nth-order active filter;
a switching circuit for switching a connection between the Nth-order active filter and the Mth-order active filter;
a power-supply control circuit for turning off a power-supply of one of the Nth-order active filter and the Mth-order active filter, where the power supply is turned off for that active filter which one is opened by the switching circuit; and
a passive element control circuit for controlling a constant of a passive element of one of the Nth-order active element and the Mth-order active element,
wherein the passive element control circuit switches a passive element of a first active filter, of which power supply is turned off by the power-supply control circuit, to function as a passive element of a second active filter, of which power supply is turned on.
7. A receiver comprising:
a mixer; and
a filter circuit coupled to an output side of the mixer;
wherein the filter circuit includes:
an Nth-order active filter;
a switching circuit for switching at least a part of the Nth-order active filter to be shorted or not to be shorted;
a power-supply control circuit for turning off a power supply of at least the part of the Nth-order active filter when the switching circuit shorts at least the part of the Nth-order active filter; and
a passive element control circuit for controlling a constant of a passive element of the Nth-order active filter,
wherein the passive element control circuit switches the passive element of the Nth-order active filter, of which power supply is turned off by the power-supply control circuit, to function as a passive element of the Nth-order active filter of which power supply is turned on.
8. The receiver of claim 7 further comprising a detector coupled to an output side of the filter circuit for detecting an interference wave level,
wherein the receiver controls the switching circuit and the power-supply control circuit in response to the interference wave level detected by the detector.
9. The receiver as defined in claim 7 , wherein the receiver controls the power supply of the Nth-order active filter, which is opened by the switching circuit, to be turned off in response to a stop of analog broadcasting.
10. An electronic device employing the receiver as defined in claim 7 .
11. A receiver comprising:
a mixer; and
a filter circuit coupled to an output side of the mixer;
wherein the filter circuit includes:
an Nth-order active filter;
an Mth-order active filter coupled in parallel with the Nth-order active filter;
a switching circuit for switching a connection between the Nth-order active filter and the Mth-order active filter;
a power-supply control circuit for turning off a power-supply of one of the Nth-order active filter and the Mth-order active filter, where the power supply is turned off for that active filter which one is opened by the switching circuit; and
a passive element control circuit for controlling a constant of a passive element of one of the Nth-order active element and the Mth-order active element,
wherein the passive element control circuit switches a passive element of a first active filter, of which power supply is turned off by the power supply control circuit, to function as a passive element of a second active filter, of which power supply is turned on.
12. The receiver of claim 11 further comprising a detector coupled to an output side of the filter circuit for detecting an interference wave level,
wherein the receiver controls the switching circuit and the power-supply control circuit in response to the interference wave level detected by the detector.
13. The receiver as defined in claim 11 ,
wherein the receiver controls the power supply of the Nth-order active filter, which is opened by the switching circuit, to be turned off in response to a stop of analog broadcasting.
14. An electronic device employing the receiver as defined in claim 11 .