The present invention relates to the control of a transmission output of a radio.
For a radio which must stably hold transmission output power, it is very important to stably maintain the gain of a transmitting circuit at all times.
To realize such a radio, various types of transmission output control have already been carried out. The transmission output control can be broadly classified into an open loop type, in which the gain of a transmitting circuit is stabilized by means of an output from a temperature sensor or a temperature-detecting element, such as a thermistor; and a closed loop type, in which the gain of the transmitting circuit is stabilized through use of an output from a detection circuit provided in the final stage of the transmitting circuit.
The transmission output control of the former type has the advantage of comparative simplicity and less expense, as well as of being able to intentionally and readily change the transmission output. On the other hand, the individual difference in the temperature characteristics of the components constituting the temperature-detecting element and the transmitting circuit makes it impossible to ensure sufficient accuracy of gain. The transmission output control of the latter type requires a detection circuit which is provided in the final stage of the transmitting circuit and is the only element that may adversely affect the accuracy of gain. For this reason, the transmission output control of the closed loop type-provides the accuracy of gain better than that provided by the transmission output control of the open loop type. On the other hand, the extent of variation in the transmission output power is determined by the extent of detection of the detection circuit. Therefore, the transmitting circuit, which intentionally changes the transmission output power, will become very complicated in configuration and expensive.
In the case of the foregoing existing technique being applied to a radio which transmits a signal through a control channel or a call channel by use of one transmitting circuit, and which intentionally changes the transmission output of the call channel while constantly maintaining the transmission output of the control channel, e.g., a base station for use with a simplified portable telephone which employs a time-division multiplexing method, a sufficient accuracy of transmission output cannot be achieved by the open loop method. The closed loop method suffers the problem of limiting the extent of change in the transmission output or involves the monitoring of a detection value output from the detection circuit for each transmission.
To solve the foregoing problems, the present invention provides a radio which transmits a signal through a control channel or a call channel by use of one transmitting circuit and which intentionally changes the transmission output of the call channel, the improvement being characterized by comprising: a closed loop which is formed, at the time of transmission of a signal through the control channel, in order to feed back a detection output value of the transmission output of the control channel to a transmission output control section to thereby control the transmission output of the control channel, and which is canceled at the time of transmission of a signal through the call channel, thereby controlling the transmission output of the call channel.