Automatic gain controller outputting control value varying nonlinearly, and a method of outputting a gain control signal thereof

An automatic gain controller having an estimator to estimate the level of an input signal, a subtractor to calculate a difference between the level estimated by the estimator and a predetermined reference value, a gain controller to output a control value achieved by scaling non-linearly the difference output by the subtractor, an accumulator to accumulate the output of the gain controller, and a modulator to modulate the output of the accumulator to a pulse width modulated signal. The gain controller outputs the control value proportional to a square of the difference. If en error between the power of the input signal and the reference value is great, the power can be quickly adjusted to a desired signal level, and if the error is small, the gain can be controlled finely.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No. 2002-115 filed on Jan. 2, 2002, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an automatic gain controller, and more particularly, to an automatic gain controller outputting a gain control signal to automatically control a signal gain inputted into a signal receiver such as a digital television.

2. Description of the Related Art

A signal receiver such as a digital television has an automatic gain controller to control the gain of the inputted signal. In case the power of the inputted signal is either excessive or low, it is difficult to properly control the signal and therefore the automatic gain controller automatically adjusts the gain of the inputted signal to an appropriate level.

The automatic gain control is necessary particularly in digital communication. In the digital communication, an analog-to-digital converter samples an analog signal passed through a radio frequency channel, and the digitalized signal undergoes a digital signal processing. When an analog signal is digitalized, an input signal needs to have a sufficient amount of power in order to minimize quantizing noise. However, if the power of the signal input is excessive, the AD converter becomes saturated and a circuit processing a digital signal causes mis-operation. Therefore, the level of the input signal should be adjusted to a certain level.

The automatic gain controller is necessary not only for a digital television but for all communication devices including a mobile communication device, etc.FIG. 1illustrates a conventional automatic gain controller, and more particularly, an automatic gain controller used for digital communication.

As illustrated inFIG. 1, a conventional automatic gain controller comprises a power estimator11, a subtractor13, a gain multiplier15, an accumulator20, and a modulator30.

The power estimator11receives a digital signal outputted from an AD converter and estimates the power of the input signal. The subtractor13calculates the value of a difference between the power estimated by the power estimator11and a predetermined reference value, i.e., an error of the signal power. The calculated difference value is inputted into the gain multiplier15which multiplies the difference value by a constant gain K. The constant gain K multiplied by the value of the difference between the reference value and the actual power of an input signal determines the bandwidth of the automatic gain controller.

The accumulator20comprises a delay unit23to delay the signal input and an adder21to add the output of the delay unit23and the output of the gain multiplier15and input the outcome into the delay unit23. The output value of the gain multiplier15is accumulated by the accumulator20.

The modulator30modulates the output value of the accumulator20. A Σ-Δ DA converter generating a pulse width modulation signal corresponding to the output of the accumulator20is used as a modulator30. The output of the modulator30is provided to other parts in a signal receiver, such as an IF amplifier or an RF amplifier requiring a gain control signal.

However, the above conventional automatic gain controller has a problem that the signal level of the input signal might not be properly adjusted when the status of the channel receiving the input signal changes too much since the gain value K controlling bandwidth is fixed. For example, as illustrated inFIG. 2, if the gain value K is set too low (K<1), it is difficult to follow the change of the input signal as the gain of the automatic gain controller becomes low, and if the gain value K is set too high (K>1), a jitter occurring at the state of the input signal being stably received may become high because the gain of the automatic gain controller becomes high.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide an automatic gain controller that is able to quickly adjust the power of the input signal to a desired signal level by letting the controller have a large gain value when a difference between the input signal power and the reference value is great, and also able to control the gain finely by letting the controller have a small gain value when the difference is small.

The foregoing and other objects of the present invention are achieved by providing that the automatic gain controller includes an estimator to estimate the level of a signal input, a subtractor to calculate a difference between the level estimated by the estimator and a predetermined reference value, and a gain controller to output a control value achieved by nonlinearly scaling the difference output from the subtractor.

The gain controller comprises a first multiplier to multiply a predetermined constant gain by the difference from the subtractor, an absolute value calculator to calculate an absolute value of the difference, and a second multiplier to output the control value by multiplying the output of the first multiplier by the output of the absolute value calculator. Then, the gain controller outputs the control value proportional to the square of the difference.

Meanwhile, the automatic gain controller according to the present invention has an accumulator to calculate accumulated values of the control value output by the gain controller, and a modulator to generate a modulated signal corresponding to the accumulated value outputted by the subtractor. The signal outputted by the modulator is provided to the device in need of a gain control signal, such as an IF amplifier.

According to the present invention, if an error between the power of the input signal and the reference value is great, the power can be quickly adjusted to a desired signal level, and if an error is small the gain can be controlled finely.

The foregoing and other objects of the present invention may also be achieved by providing a method of outputting a gain control signal of an automatic gain controller, which comprises: estimating the level of a signal input, calculating a difference between the level estimated and a predetermined reference value, and outputting a control value by nonlinearly scaling the calculated difference between the level estimated and the predetermined reference value.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3is a block diagram of an automatic gain controller according to an embodiment of the present invention, andFIG. 4is a block diagram illustrating a detailed construction of the gain controller inFIG. 3. In the present embodiment, an automatic gain controller outputting a gain control signal for a digital signal is provided.

A signal received through an external channel is converted to a digital signal by an AD converter (not shown) and the converted digital signal is inputted into the automatic gain controller according to this embodiment of the present invention.

The automatic gain controller comprises a power estimator51, a subtractor53, a gain controller60, an accumulator70, and a modulator80.

The power estimator51receives a digital signal outputted by an AD converter and estimates the power of the input signal. The power of the input signal can be calculated either by using a square value of the input signal or simply by adopting an absolute value of the input signal.

The output of the power estimator51and a predetermined reference value are inputted into the subtractor53. The reference value is set to a certain value that is calculated under the assumption that the input signal has a normal distribution. The reference value is stored in a storage unit such as a register (not shown) and is changeable depending on the need. The subtractor53calculates a difference, i.e., an error of the power signal, between the power estimated in the power estimator11and the reference value. The calculated difference value is inputted into the gain controller60.

The gain controller60is comprised of a first multiplier61, a second multiplier65and an absolute value calculator63as illustrated inFIG. 4. Into the first multiplier61is input the difference outputted by the subtractor53, and the first multiplier61multiplies a predetermined constant gain K by the difference. The difference outputted by the subtractor53is also inputted into the absolute value calculator63, and the absolute value calculator63calculates the absolute value of the difference outputted by the subtractor53. The second multiplier65multiplies the output of the first multiplier61by the output of the absolute value calculator63, and the output of the second multiplier65becomes a control value outputted by the gain controller60.

The output of the gain controller60having the above construction can be expressed by the following formula:

In this formula, n is a sampling time for the digital input signal;

y(n) is the output of the gain controller60;

K is a constant gain of the first multiplier61; and

e(n) is an error outputted by the subtractor53.

As shown in the above formula, the gain controller60outputs the control value by nonlinearly scaling the inputted difference, and the outputted control value is proportional to the square of the difference outputted by the subtractor53.

The accumulator70comprises a delay unit73to delay a signal input thereto, and an adder71to add the output of the delay unit73and the output of the gain controller60and input the output thereof to the delay unit73. The delay unit73delays the signal input thereto as long as one sample period. Since the input of the delay unit73is the output of itself and the gain controller60, the delay unit73consecutively accumulates the output of the gain controller60. Therefore, the accumulator70accumulates every control value outputted by the gain controller60, and then calculates the accumulated value.

The modulator80modulates the output value of the accumulator70. A Σ-Δ DA converter to generate a pulse width modulation signal corresponding to the output of the accumulator70is preferably used as the modulator80. Accordingly, the modulator80generates a pulse width modulation signal comprised of either a binary value of 1 or 0, and this signal becomes a final output of the automatic gain controller. The final output generated by the modulator80is provided to other parts by a signal receiver, such as an IF amplifier or an RF amplifier requiring a gain control signal.

FIG. 5is a graph illustrating the output of the gain controller60indicated in the above formula. As illustrated inFIG. 5, the greater the value of the difference between the estimated level of the input and the predetermined reference value, which is an error of signal input power and the reference value, the greater the gain of the automatic gain controller is as a secondary function. Therefore, the level change of the signal input can be quickly followed and the movement of the signal receiver becomes quickly stabilized. In addition, the gain becomes smaller when the above difference value is small. As a result, fluctuation caused by an unnecessarily large gain does not occur in the signal level, and high jitter occurring at the state of the input signal being stably received is prevented.

The above embodiment explains an example of the control value proportional to a square of an error so as to quickly follow the level change of the input signal when the level of the input signal changes greatly. However, various methods may be applied to nonlinearly increase the control value as the value of an error increases. For example, one of the possible methods could be making the gain controller proportional to a cube of an error, or employing various circuits, in which the characteristics of the gain is changeable according to another nonlinear characteristic that can not be indicated in a specific formula.

As described above, according to the present invention, if an error between the power of the input signal and the reference value is great, the power can be quickly adjusted to a desired signal level, and if the error is small, the gain can be controlled finely.