The present invention relates to a receiving apparatus and a power control method, in particular, to a receiving apparatus configured to reduce its standby power consumption to a minimum, and a power control method.
In recent years, digital satellite broadcasts are coming into wider use. The digital satellite broadcasts are capable of transmitting a high quality signal as compared with existing analogue broadcasts, and are designed to use a multi channel method. Concerning such digital satellite broadcasts, a plurality of specialized channels for sports, movies, music, news, etc., are prepared. A receiving apparatus of a user receives only channels selected from among the plurality of specialized channels, for which the user makes contract.
By the way, in order to receive channels for which a user makes contract (limited receiving), it is necessary to receive individual information of each user (EMM: Entitlement Management Message), which is sent from a sending side, and to store it in a receiving apparatus beforehand.
That is to say, concerning conventional receiving apparatuses, radio waves received by an antenna are amplified and frequency-converted in a high-frequency portion. Moreover, required processing including PSK demodulation and error correction is performed for the frequency-converted data in a DSP (Digital Signal Processor). The high-frequency portion and the DSP are generally housed in one shielded case, which is called a front-end portion. Then, a transport stream, which is output from the front-end portion, is separated into audio data, video data, program specification information, and the like by a demultiplexer, and is judged whether or not a desired EMM has been received. If a result of the judgment is that the desired EMM has been received, that EMM is stored.
Accordingly, the receiving apparatus should always be in a power-on state (energized state) for the purpose of receiving an EMM, which is transmitted unexpectedly; and in order to judge whether or not the EMM is desired one, circuits such as a demultiplexer circuit are required to be operated. Therefore, there is a problem of high power consumption even in a standby state (standby power consumption).
For these reasons, in Japanese Patent Laid-Open No. Hei 11-317713, the following technology is disclosed: on a transmission side, EMM transmission-schedule information, in which scheduled time of EMM transmission is described, is transmitted; and on a receiving side, after the received EMM transmission-schedule information is analyzed, transmission time of EMM, whose destination is that on the receiving side, is stored. This permits power supplies for portions other than CPU (Central Processing Unit) to be turned off while a program is not viewed, which minimizes standby power consumption.
However, in the case of this technology, there is a cost problem because existing transmission apparatuses additionally require a function of generating EMM transmission-schedule information.