Automatic gain control apparatus of cable modem, and lock-time acquisition method using the same

Abstract

Provided is an automatic gain control (AGC) apparatus of a cable modem. The apparatus includes: a gain controller for measuring a power level of digital input signals transmitted from outside, accumulating the measured values of the digital input signals for a predetermined period, acquiring an average size of the signals, and calculating an error value between the average signal size and a predetermined signal size; an amplitude control unit for receiving error values adjusted by the gain controller and controlling an amplitude of the signal; a low pass filter for receiving the signal outputted from the amplitude control unit and performing low pass filtering on the signal; and a signal size control unit for receiving the signal obtained from filtering of the low pass filter and controlling the signal size.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which:

FIG. 1 is a flowchart describing a conventional automatic gain control method;

FIG. 2 is a block diagram showing an automatic gain control (AGC) apparatus of a cable modem in accordance with an embodiment of the present invention; and

FIG. 3 is a flowchart describing a lock-time acquisition method using the automatic gain control apparatus in accordance with an embodiment of the present invention.

Claims

1. An automatic gain control (AGC) apparatus of a cable modem, comprising: a gain control means for measuring a power level of digital input signals transmitted from outside, accumulating the measured values of the digital input signals for a predetermined period, acquiring an average size of the signals, and calculating an error value between the average signal size and a predetermined signal size;an amplitude control means for receiving error values adjusted by the gain control means and controlling an amplitude of the signal;a low pass filtering means for receiving the signal outputted from the amplitude control means and performing low pass filtering on the signal; anda signal size control means for receiving the signal obtained from filtering of the low pass filtering means and controlling the signal size.

2. The apparatus as recited in claim 1, wherein the gain control means includes: a power detecting unit for measuring power level of a reception signal;a power accumulating unit for accumulating power level values to acquire an average value of the power levels detected in the power detecting unit;a power averaging unit for acquiring an average power level of the signal based on the value accumulated in the power accumulating unit;a signal size detecting unit for acquiring a signal size based on a result value of the power averaging unit; andan error detecting unit for calculating an error value between an inputted average signal size and a predetermined signal size.

3. The apparatus as recited in claim 1, wherein the amplitude control means includes an amplifier for loop gain of the signal, a delayer for comparison with a previous signal to control the amplitude, and an adder for adding the previous signal to a present signal.

4. The apparatus as recited in claim 1, wherein the low pass filtering means includes two amplifiers for amplifying the gain to perform low pass filtering, a delayer and an adder.

5. The apparatus as recited in claim 1, wherein the signal size control means includes an amplifier for controlling the signal size.

6. A lock-time acquisition method of an automatic gain control (AGC) apparatus in a cable modem, comprising the steps of: a) setting up a reference signal size and a lock threshold, and initializing a loop filter, a low pass filter and gain of a gain control amplifier;b) measuring a size of a signal transmitted from outside and calculating an error between the signal size and the reference signal size;c) accumulating errors between the measured two signals for a predetermined window period to acquire an average error;d) comparing the accumulated average error value with the lock threshold; ande) when the average error value converges into the lock threshold, deallocating a lock-time.

7. The method as recited in claim 6, further comprising the steps of: f) when the average error value does not converge into the lock threshold, comparing the average error value with diverge threshold and checking whether a symbol count exists within the total number of symbols; andg) when the symbol count exists in the total number of symbols, operating again the procedure after reset of the entire signals and when the symbol count is out of the total number of symbols, transmitting an automatic gain control failure message.

8. The method as recited in claim 6, wherein in the step e), a symbol count value is deallocated at a lock-time to acquire the lock-time when the signal level starts to be regularly maintained by automatic gain control.