RF signal automatic gain control method

The automatic gain control (AGC) method contains the following steps: producing a feedback signal and transmitting the feedback signal to a signal processing unit to produce a working signal; transmitting the working signal to a first signal control unit to produce a first control voltage; transmitting the first control voltage to a second signal control unit to produce a second control voltage, which is a fixed voltage; and transmitting the second control voltage to an AGC unit where the fixed second control voltage is used as a reference value. As such, when a radio-frequency (RF) input signal varies due to channel loading variation, an RF output signal by the AGC unit can be maintained within a specified dB range.

BACKGROUND OF THE INVENTION

(a) Technical Field of the Invention

The present invention is generally related to an automatic gain control method for radio-frequency (RF) signal, and more particular to a RF signal automatic grain control method capable of maintaining RF output signal within a specified dB range.

(b) Description of the Prior Art

Electronic devices are often operated under various control circuits to achieve desired performance. Feedback is a major mechanism utilized by numerous control circuits and therefore they are often named as feedback control circuits. The so-called automatic gain control (AGC) circuit is one such control circuit.

AGC circuit is commonly applied in radio-frequency (RF) reception devices. This is due to that RF signal suffers significant fluctuation resulted from factors like multiple paths and attenuation in the transmission process. The AGC circuit is used to maintain the stability of RF output signal's dB value.

For conventional AGC circuit, once channel loading to the RF input signal changes, a reference value fed back by the AGC circuit has to be manually adjusted to as to maintain the stability of RF output signal's dB value, which is cumbersome to operation personnel.

SUMMARY OF THE INVENTION

To obviate the shortcomings of prior art, a novel automatic gain control (AGC) method is provided herein. The AGC method contains the following steps: producing a feedback signal and transmitting the feedback signal to a signal processing unit to produce a working signal; transmitting the working signal to a first signal control unit to produce a first control voltage; transmitting the first control voltage to a second signal control unit to produce a second control voltage, which is a fixed voltage; and transmitting the second control voltage to an AGC unit where the fixed second control voltage is used as a reference value. As such, when a radio-frequency (RF) input signal varies due to channel loading variation, an RF output signal by the AGC unit can be maintained within a specified dB range.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown inFIGS. 1 to 3, an automatic gain control (AGC) method for radio-frequency (RF) signal according to the present invention is implemented in an AGC system which contains an AGC unit1, a distributor2, an AGC circuit3, and a selector4.

The AGC unit1is to adjust the strength of an input RF signal.

The distributor2is electrically connected to an output terminal of the AGC unit1, and produces a feedback signal. The distributor2has a first output terminal21and a second output terminal22. An output RF signal is provided on the first output terminal21and the feedback signal is provided on the second output terminal22.

The AGC circuit3is electrically connected to the second output terminal22of the distributor2. The AGC circuit3contains a signal processing unit31, a first signal control unit32, and a second signal control unit33. The signal processing unit31receives the feedback signal from the distributor2, and produces a working signal as output. The first signal control unit32is electrically connected to an output terminal of the signal processing unit31and receives the working signal. The first signal control unit32converts the working signal into a first control voltage as output. The first signal control unit32varies the first control voltage according to its channel loading. The second signal control unit33is electrically connected to an output terminal of the first signal control unit32and to the AGC unit1. The second signal control unit33receives the first control voltage from the first signal control unit32and converts the first control voltage into a second control voltage according to the channel loading of the second signal control unit33. As the second signal control unit33provides compensation according to its channel loading, the second control voltage is a fixed voltage. The second control voltage is then transmitted to the AGC unit1.

The selector4is electrically connected to the AGC circuit3and the AGC unit1. More specifically, the selector4is electrically connected to an output terminal of the second signal control unit33and to the AGC unit1. The selector4allows one of an AGC signal or a RGC signal to pass, and transmits the second control voltage.

As shown inFIG. 3, an AGC method according to an embodiment of the present invention contains the following steps.

In step100, a feedback signal is produced.

In step110, the feedback signal is transmitted to the signal processing unit31to produce a working signal, where the working signal can be a DC voltage.

In step120, the working signal is transmitted to the first signal control unit32to produce a first control voltage, where the first control voltage varies depending on the channel loading to the first signal control unit32.

In step130, the first control voltage is transmitted to the second signal control unit33to produce a second control voltage, which can be a fixed voltage as the second signal control unit33provides compensation in accordance with its channel loading.

In step140, the second control voltage is transmitted to the AGC unit1.

If the RF input signal is an AGC signal, the second control voltage produced by the second signal control unit33can be directly transmitted to the AGC unit1as a reference value. As such, when the RF input signal varies due to channel loading variation, the RF output signal by the AGC unit1through the first output terminal21of the distributor2can be maintained within a specified dB range.

As shown inFIG. 4, an AGC method according to another embodiment of the present invention contains the following steps.

In step200, a feedback signal is produced.

In step210, the feedback signal is transmitted to the signal processing unit31to produce a working signal, where the working signal can be a DC voltage.

In step220, the working signal is transmitted to the first signal control unit32to produce a first control voltage, where the first control voltage varies depending on the channel loading to the first signal control unit32.

In step230, the first control voltage is transmitted to the second signal control unit33to compensate the variation due to the channel loading and produce a second control voltage. In other words, the second control voltage is for compensating the variation resulted from the channel loading change.

In step240, the second control voltage is transmitted to the selector4.

In step250, the second control voltage is transmitted to the AGC unit1.

Alternatively, the selector4is for selecting an AGC control signal or a RGC control signal to pass, and transmits the second control voltage which is a fixed voltage to the AGC unit1. The fixed second control voltage is as a reference value so that, when the RF input signal varies, the RF output signal by the AGC unit1through the first output terminal21of the distributor2can be maintained within a specified dB range.

In the above steps120and220, when the first control voltage is under a fully channel loaded condition, the first control voltage is transmitted to the second signal control unit33, which directly produces the second control voltage.

In the above steps120and220, when the first control voltage is under a not fully channel loaded condition, the first control voltage is transmitted to the second signal control unit33, where the second signal control unit33produces the second control voltage in accordance with a pre-determined adjustment method. The adjustment method can be one by digitally setting a preset voltage to the second signal control unit33, or one by manually setting a preset voltage to the second signal control unit33.

The AGC circuit can further contain a signal average unit electrically connected between the first and second signal control units32and33. The first control voltage produced by the first signal control unit32is first transmitted into the signal average unit, and then into the second signal control unit33so as to produce the second control voltage. Under this condition, the second signal control voltage can be a Quadrature Amplitude Modulation (QAM) signal. While certain novel features of this invention have been shown and described and are pointed out in the annexed claim, it is not intended to be limited to the details above, since it will be understood that various omissions, modifications, substitutions and changes in the forms and details of the device illustrated and in its operation can be made by those skilled in the art without departing in any way from the spirit of the present invention.