KR20100050679A - Device and method for calibrating cutoff frequency of analog filter - Google Patents

Abstract

PURPOSE: According to the cut-off frequency calibrating apparatus of the analog filter and method thereof is the situation of the received signal and the interferential signal which is near, the cut-off frequency which guarantees the always uniform performance by it minutes, changeably adjusting the cut-off frequency of the analog filter, is obtained. CONSTITUTION: A digital signal having the gain which the digital filter(150) is adjusted is input. The digital filter filters the channel signal of the frequency band wanting among inputted signals. The power level of the signal inputted with the first power detector(160) is the digital filter is calculated. The second power detector(170) calculates the power level of the signal outputted in the digital filter.

Description

Cutoff frequency correction device of analog filter and method thereof {DEVICE AND METHOD FOR CALIBRATING CUTOFF FREQUENCY OF ANALOG FILTER}

The present invention relates to an apparatus and method for compensating a cutoff frequency of an analog filter for adjusting a cutoff frequency of an analog filter in a baseband according to a situation of a received signal and an adjacent signal.

Analog filters employed in receivers, such as broadcast receivers, tend to change randomly in the cut-off frequency, which is a major characteristic, as the process changes.

A method of compensating the cutoff frequency of a conventional analog filter includes a circuit (compensation circuit) having a resistance (R) and a capacitor (C) similar to the passive elements (R, C) used in the analog filter. In this compensation circuit, the process changes of resistors and capacitors are sensed through RC delay, and a value is applied to the analog filter to compensate for this.

In other words, the desired capacitance can be found by variably adjusting the capacitor to have a RC delay time closest to a predetermined reference time (cycle of the clock) in the calibration circuit, thereby realizing the resistance or capacitance implemented through the actual process. To compensate for this, it is possible to know how much the capacitance needs to be changed. The information thus found is equally applied to the capacitance of the analog filter, thereby having a cutoff frequency close to the ideal cutoff frequency.

As such, the cutoff frequency, which is determined once using the correction circuit, always maintains the same value regardless of the environmental change of the received signal. Therefore, the desired received signal is coming in small or large, or adjacent signals that interfere with reception are coming in large or small, or always operate with a constant cutoff frequency.

The object of the present invention is not only to correct for the cutoff frequency for the analog filter in the baseband, but also to adjust the fine cutoff frequency according to the situation of the received signal and the adjacent signal without fixing the corrected value so that the actual signal is received. The present invention provides an apparatus and method for compensating a cutoff frequency of an analog filter capable of determining a cutoff frequency in an optimized form according to various environments.

Technical problems to be achieved by the present invention are not limited to the above-mentioned technical problems, and other technical problems not mentioned above may be clearly understood by those skilled in the art from the following description. There will be.

Technical means of the present invention for achieving the above object, a digital filter for receiving a digital signal whose gain is adjusted and filters the channel signal of the desired frequency band of the input signal; A first power detector for detecting a signal input to the digital filter and calculating a power level of the detected signal; A second power detector for detecting a signal output from the digital filter and calculating a power level of the detected signal; And a filter correction unit configured to determine and control the cutoff frequency of the analog filter by subtracting the power level input from the first power detector and the power level input from the second power detector and comparing the subtracted difference value with a set reference value. Characterized in that it comprises a.

The analog filter may filter the channel signal of a specific frequency band of the input signal according to the cutoff frequency controlled by the filter correction part and output the filtered channel signal to the digital filter side.

In detail, the power level calculated by the first and second power detectors is either the sum of the maximum power level of the detected signal and the total power level of the detected signal or the average value of the detected signal. The reference value of the filter correction unit is variable every moment within approximately 10% of the power level detected by the first power detector, or is fixed or preset to a predetermined value.

The filter correction unit controls the cutoff frequency of the analog filter when the value obtained by subtracting the power level of the first power detector and the power level of the second power detector is larger than the reference value, and controls the power level and the first power detector of the first power detector. 2 If the power level of the power detector is subtracted from the value equal to or less than the reference value, the cutoff frequency of the analog filter is maintained in the current state.

The analog filter may include an amplifier for inverting and amplifying a phase of an input signal; A resistor installed at an inverting input terminal of the amplifier; A plurality of capacitors installed in parallel between the inverting input terminal and the output terminal of the amplifier; And switch means installed in series with each capacitor to open and close according to a control signal of the filter correction unit.

The technical method of the present invention for achieving the above object comprises: a first step of filtering a channel signal including a desired frequency band of the input analog signal according to the set cutoff frequency; A second step of converting a gain-adjusted analog signal into a digital signal after adjusting the gain of the filtered signal; A third step of filtering and outputting a channel signal of a desired frequency band among the converted digital signals; A fourth step of detecting a digital signal before the third step is performed and calculating a power level of the detected signal; A fifth step of detecting a digital signal after the third step is performed and calculating a power level of the detected signal; And a sixth step of determining and controlling the cutoff frequency of the analog signal by subtracting the power level calculated in the fourth step and the power level calculated in the fifth step and comparing the subtracted difference value with the set reference value. It is characterized by performing.

As described above, the present invention has an advantage of determining the cutoff frequency in an optimized form according to various environments in which an actual signal is received.

In addition, by fine-tuning the cutoff frequency of the analog filter in accordance with the situation of the received signal and the adjacent interference signal, it is possible to obtain a cutoff frequency that ensures uniform performance at all times regardless of the analog filter process changes in terms of production yield. Advantageously, the accuracy of the cutoff frequency correction due to the resistance of the resistor and the capacitor in the analog filter can be overcome.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a circuit block diagram illustrating an apparatus for compensating a cutoff frequency of an analog filter according to an exemplary embodiment of the present invention, which includes an RF receiver 110, an analog filter 120, a variable gain amplifier 130 (VGA), and an AD converter 140; ADC), a digital filter 150, a first power detector 160, a second power detector 170, an automatic gain control unit 180 (AGC) and a filter correction unit 190.

The RF receiver 110 includes a mixer for synthesizing an input RF signal with a local signal corresponding to a selected channel and outputting a down-converted Low IF or Zero IF signal. The mixer may be any type of mixer, and includes an image rejection mixer, a quadrature mixer, and a harmonic rejection mixer.

The analog filter 120 filters out a specific frequency band according to a preset cutoff frequency among the low IF or zero IF signals input from the RF receiver 110 to output a low pass filter (LPF) or a band pass (BPF). filter). The frequency of the signal input to the analog filter 120 is always a signal of a constant frequency is input according to the down conversion (down conversion) of the RF receiver 110 irrespective of the selected channel.

In general, the analog filter 120 has a filtering band and its center frequency fixed to a predetermined value through a predetermined correction process. However, the center frequency and the filtering band of the analog filter 120 have a unique error and an external circuit. It is changed by the connection of, and ambient and its own temperature, which requires correction of the cutoff frequency.

The variable gain amplifier 130 is configured to amplify the signal input from the analog filter 120 by a level required by the AD converter 140 at a later stage. The variable gain amplifier 130 has a variable gain in accordance with a control signal of the automatic gain control unit 180.

The analog to digital converter (AD converter 140) is configured to convert the analog signal input from the variable gain amplifier 130 into a digital signal.

The digital filter 150 is configured to pass only a signal of a frequency band to be received. The digital filter 150 has better cutoff frequency characteristics or skirt characteristics than the analog filter 120, so that only the signal of a desired frequency band can be accurately filtered.

The first power detector 160 is configured to detect a signal input to the digital filter 150 and calculate a power level of the detected signal. In the case of the analog filter 120, not only the frequency band to be received but also a portion of the adjacent interference signal are passed due to the cutoff frequency and the skirt characteristic. Accordingly, the signal detected by the first power detector 160 is intended to be received. Not only the signal but also a portion of the adjacent signal is included, which causes the first power detector 160 to consider both the signal level to be received and the power level of the adjacent interference signal.

The second power detector 170 is configured to detect a signal output from the digital filter 150 and calculate a power level of the detected signal. In the case of the digital filter 150, since the cutoff frequency and the skirt characteristic are excellent, only the signal of the frequency band to be received is passed. Accordingly, the second power detector 170 considers only the power level of the signal to be received. Done.

When the first power detector 160 and the second power detector 170 calculates the power level of the detected signal, the maximum power level of the detected signal may be calculated, or the sum or average of the total power levels may be calculated. In this case, any of these methods may be used.

The automatic gain control unit 180 compares the power level input from the first power detector 160 with the preset power level, so that the variable gain amplifier 130 has a set amplitude such that the amplitude of the signal input to the AD converter 140 becomes a set amplitude. To control the gain.

The filter correction unit 190 subtracts the power level input from the second power detector 170 from the power level input from the first power detector 160, and compares the subtracted difference value with the set reference value. Determine and control the cutoff frequency of filter 120 to be optimized. For example, the filter correction unit 190 reduces the cutoff frequency of the analog filter 120 when the value obtained by subtracting the power level of the first power detector 160 and the power level of the second power detector 170 is greater than the reference value. The capacitance of the analog filter 120 is controlled in the direction, and the value obtained by subtracting the power level of the first power detector 160 and the power level of the second power detector 170 is equal to or smaller than the reference value. Will maintain the current cutoff frequency.

The setting of the reference value of the filter correction unit 190 may include a variable allocation method and a fixed setting method. The variable allocation scheme means that the variable allocation scheme is allocated every second within about 10% of the power level detected by the first power detector 160, and the fixed setup scheme means that the fixed setup scheme is fixed and set in advance to a predetermined value.

In the case of the analog filter 120 according to the present invention can be simply configured as shown in Figure 2, the analog filter 120 is an amplifier (Amp) and a resistor (R), a plurality of capacitors (C1 ~ Cn) and a plurality of switches It consists of means (S1-Sn).

The amplifier Amp inverts and amplifies the phase of the input signal, and a resistor R is provided at an inverting input terminal (-) of the amplifier Amp, and a plurality of capacitors C1 to Cn are connected to the amplifier Amp. Are arranged in parallel between the inverting input terminal (-) and the output terminal of (), and the switch dimension stages (S1 to Sn) are installed in series with the respective capacitors (C1 to Cn) in accordance with the control signal of the filter correction unit 190. It is comprised by the transistor which opens and closes.

As the switch means S1 to Sn are turned on, the capacitance of the analog filter 120 increases but the cutoff frequency decreases. Accordingly, the filter correction unit 190 properly adjusts the capacitance of the analog filter 120 according to the determined cutoff frequency. For example, the filter correction unit 190 controls to increase the number of turn-on of each switch means (S1 to Sn) in the direction in which the capacitance of the analog filter 120 increases when the cutoff frequency is to be decreased. If, initially, the on and off of each switch means (S1 ~ Sn) is set (default) so as to have a minimum capacitance in the analog filter 120, the control of the filter correction 190 is controlled The implementation of the algorithm is advantageous, as well as faster access to the target capacitance.

In addition, it is preferable to set the capacitances of the capacitors C1 to Cn differently so that various capacitances can be adjusted with a small number of capacitors. For example, the n-th capacitor Cn is designed to have twice the capacitance of the n-th capacitor Cn-1.

On the other hand, when the RF receiver 110 is composed of an orthogonal mixer, the baseband circuits 120 to 190 as shown in FIG. 1 may be formed of I and Q channels, and in this case, baseband circuits of I and Q channels. Are each made of the configuration of FIG.

3 is a flowchart illustrating a cutoff frequency correction process of an analog filter according to the present invention, which will be described with reference to FIGS. 1 and 2.

First, the analog filter 120 filters and outputs the low IF or zero IF signal input from the RF receiver 110 according to the set cutoff frequency. Of course, the frequency out of the cutoff frequency of the input signal is filtered out (S1).

In this case, the analog filter 120 generally passes not only a frequency band to be received but also a portion of an adjacent interference signal.

The signal passing through the analog filter 120 is adjusted by the gain through the variable gain amplifier 130 is amplified and output to the amplitude required by the AD converter 140 of the rear stage, AD converter 140 is a variable gain amplifier The analog signal input at 130 is converted into a digital signal according to a predetermined algorithm and outputted (S2).

The digital filter 150 filters and passes only signals of a desired frequency band among the digital signals input from the AD converter 140. In the case of the digital filter 150, since the cutoff frequency and the skirt characteristic are superior to those of the analog filter 120, only the signal of the desired frequency band can be passed accurately (S3).

The first power detector 160 detects a signal input to the digital filter 150 and calculates a power level P _PD1 of the detected signal (S4). In the case of the analog filter 120, not only the frequency band to be received but also a portion of the adjacent interference signal are passed due to the cutoff frequency and the skirt characteristic. Accordingly, the signal detected by the first power detector 160 is intended to be received. Not only the signal but also a portion of the adjacent interference signal is included, which causes the first power detector 160 to consider both the signal to receive and the power level for the adjacent interference signal.

The second power detector 170 detects a signal output from the digital filter 150 and calculates a power level P _PD2 of the detected signal (S5). In the case of the digital filter 150, since the cutoff frequency and the skirt characteristic are excellent, only the signal of the frequency band to be received is passed. Accordingly, the second power detector 170 considers only the power level of the signal to be received. Done.

When the first power detector 160 and the second power detector 170 calculates the power level of the detected signal, the maximum power level of the detected signal may be calculated, or the sum or average of the total power levels may be calculated. In this case, any of these methods may be used.

Here, there may be various cases in the form of a signal input to the analog filter 120, but the two most representative cases are calculated as shown in FIGS. 4A and 4B.

In the first case, the power level of the signal N to be received is strong as shown in FIG. 4A, but the power level of the adjacent interference signal N + 1 is insignificant. In the second case, the signal to be received as shown in FIG. 4B ( The power level of N) is weak, but the power level of the adjacent interference signal N + 1 is strong.

Since the digital filter 150 does not include a passive element such as R or C, the digital filter 150 passes only the channel signal N to be received almost accurately. In this case, when the cutoff frequency of the analog filter 120 located in front of the digital filter 150 is equal to or greater than the cutoff frequency of the digital filter 150, the second power detector 170 may receive the channel signal N. ), And if the cutoff frequency of the analog filter 120 is smaller than the cutoff frequency of the digital filter 150, the second power detector 170 may monitor the power of the channel signal N to be received. Monitored value is smaller than actual value.

On the other hand, the first power detector 160 monitors the power level of a part of the interference channel signal N + 1 adjacent to the reception channel signal N according to the cutoff frequency of the analog filter 120. Depending on the cutoff frequency of 120, the proportion of power of adjacent interference signals among the monitored power levels is changed.

Subsequently, when the power level information on the digital signal is transmitted from the first and second power detectors 160 and 170, the filter correction unit 190 inputs the power level P _PD1 input from the first power detector 160. After subtracting the power level P _PD2 input from the second power detector 170, the subtracted difference value and the set reference value P _REF are compared with each other (S6).

Here, the filter correction unit 190 is a value obtained by subtracting the power level P _PD1 of the first power detector 160 and the power level P _PD2 of the second power detector 170 is greater than the reference value P _REF . In this case, the capacitance of the analog filter 120 is controlled in a direction of decreasing the cutoff frequency of the analog filter 120 (S7). If the value obtained by subtracting the power level P _PD1 of the first power detector 160 and the power level P _PD2 of the second power detector 170 is equal to or smaller than the reference value P _REF , the analog filter 120. The cutoff frequency of C1) is maintained at the current state (S8).

The adjustment of the cutoff frequency of the analog filter 120 performed by the filter correction unit 190 will be described with reference to FIGS. 5A and 5B.

First, the operation of adjusting the cutoff frequency when the power level of the reception channel signal is much larger than the power level of the adjacent interference signal will be described with reference to FIG. 5A. In FIG. 6A, when the cutoff frequency of the analog filter 120 is moved to the lower side (A direction) and to the higher side (B direction), the power level monitored by the first power detector 160 and the second side are compared. The difference between the power levels monitored by the power detector 170 does not show a large difference because the power level of the interference signal is relatively small. Therefore, in this case, a decision is made to take the cutoff frequency of the analog filter 120 a little wider, which causes a sharp worsening at the rear end of the RF receiver 110, particularly near the cutoff frequency of the analog filter 120. Can minimize the effects of the SNR value.

On the other hand, if the power level of the adjacent interference signal is significantly larger than the power level of the channel signal to be received, the operation will be described with reference to Figure 6b. In FIG. 6B, when the cutoff frequency of the analog filter 120 is moved to the lower side (C direction), the power level monitored by the first power detector 160 is gradually approaching the power level monitored by the second power detector 170. Done. On the other hand, when the cutoff frequency of the analog filter 120 is moved upward (D direction), the power level monitored by the first power detector 160 is gradually increased than the power level monitored by the second power detector 170. Done.

Accordingly, the filter correction unit 190 may determine a direction for correcting the cutoff frequency of the analog filter 120 using the respective power levels detected by the first and second power detectors 160 and 170. While gradually moving the cutoff frequency in the direction, while continuously monitoring the difference between the power levels monitored by the first and second power detectors 160 and 170, the cutoff frequency at which the power level is finally approached is determined by the analog filter 120. This is determined by the final cutoff frequency.

By optimizing the cutoff frequency of the analog filter in this way, it is possible to obtain a cutoff frequency that guarantees uniform performance at all times regardless of the process changes made on the chip, which is advantageous in terms of production yield and also in the tuner IC of the broadcast receiver. When the configuration of the present invention is used, it is possible to ensure stable reception performance in various reception environments.

This method can be usefully applied in various wireless reception environments including a tuner of a broadcast receiver as well as a wireless LAN.

Preferred embodiments of the present invention are disclosed for purposes of illustration, and those skilled in the art will be able to make various modifications, changes, and additions within the spirit of the present invention. Therefore, such modifications, changes and additions should be determined not only by the claims below, but also by equivalents to those claims.

1 is a circuit block diagram illustrating an apparatus for compensating a cutoff frequency of an analog filter according to an exemplary embodiment of the present invention.

2 is a circuit diagram showing a detailed configuration of an analog filter according to the present invention.

3 is a flowchart illustrating a cutoff frequency correction process of an analog filter according to an exemplary embodiment of the present invention.

4A and 4B are diagrams each showing a representative situation of a received signal input to an analog filter.

5A and 5B are diagrams for explaining a cutoff frequency adjusting method of an analog filter according to the present invention.

* Explanation of symbols for the main parts of the drawings

110: RF receiver 120: analog filter

130: variable gain amplifier (VGA) 140: AD converter (ADC)

150: digital filter 160: first power detector

170: second power detector 180: automatic gain control unit (AGC)

190: filter correction

Claims (12)

A digital filter that receives a digital signal whose gain is adjusted and filters and outputs a channel signal of a desired frequency band among the input signals; A first power detector for detecting a signal input to the digital filter and calculating a power level of the detected signal; A second power detector for detecting a signal output from the digital filter and calculating a power level of the detected signal; And A filter correction unit for determining and controlling the cutoff frequency of the analog filter by subtracting the power level input from the first power detector and the power level input from the second power detector and comparing the subtracted difference value with a set reference value; Cutoff frequency correction device of an analog filter. The method of claim 1, And the analog filter filters the channel signal of a specific frequency band of the input signal according to the cutoff frequency controlled by the filter correction and outputs the channel signal to the digital filter. The method according to claim 1 or 2, The power level calculated by the first and second power detectors is either the sum of the maximum power level of the detected signal and the total power level of the detected signal or the average value of the detected signal. Correction device. The method according to claim 1 or 2, The reference value of the filter correction unit, the cutoff frequency correction device of the analog filter, characterized in that the variable is assigned every second within approximately 10% of the power level detected by the first power detector or is fixed to a predetermined value in advance. The method according to claim 1 or 2, The filter correction unit controls the cutoff frequency of the analog filter when the value obtained by subtracting the power level of the first power detector and the power level of the second power detector is larger than the reference value, and controls the power level and the first power detector of the first power detector. 2, wherein the cutoff frequency of the analog filter is maintained in the current state when the value of the power detector subtracted from the power level is equal to or smaller than the reference value. The method according to claim 1 or 2, The analog filter is a low-pass filter or a band pass filter, characterized in that the cutoff frequency correction device of the analog filter. The method according to claim 1 or 2, The analog filter, An amplifier for inverting and amplifying the phase of the input signal; A resistor installed at an inverting input terminal of the amplifier; A plurality of capacitors installed in parallel between the inverting input terminal and the output terminal of the amplifier; And switch means installed in series with each of the capacitors to be opened and closed according to a control signal of the filter correction unit. The method of claim 7, wherein The cutoff frequency correction device of the analog filter, characterized in that the capacitance of the analog filter increases but the cutoff frequency decreases as each switch means is turned on. A first step of filtering a channel signal including a desired frequency band among the input analog signals according to the set cutoff frequency; A second step of converting a gain-adjusted analog signal into a digital signal after adjusting the gain of the filtered signal; A third step of filtering and outputting a channel signal of a desired frequency band among the converted digital signals; A fourth step of detecting a digital signal before the third step is performed and calculating a power level of the detected signal; A fifth step of detecting a digital signal after the third step is performed and calculating a power level of the detected signal; And Subtracting the power level calculated in the fourth step and the power level calculated in the fifth step, and then variably determining and controlling the cutoff frequency of the analog signal by comparing the subtracted difference value with the set reference value; Cutoff frequency correction method of the analog filter, characterized in that for performing. The method of claim 9, The power level calculated in the fourth and fifth steps is any one of the sum of the maximum power level of the detected signal and the total power level of the detected signal or the average value of the detected signal. Calibration method. 11. The method according to claim 9 or 10, The reference value in the sixth step is variable every minute within approximately 10% of the power level detected in the fourth step is assigned or fixed in advance to a predetermined value cut-off frequency correction method of the analog filter. 11. The method according to claim 9 or 10, In the sixth step, if the value obtained by subtracting the power level calculated in the fourth step and the power level calculated in the fifth step is larger than a reference value, the sixth step is controlled in a direction of decreasing the cutoff frequency of the analog signal, and the fourth step. If the value obtained by subtracting the power level calculated in step 5 and the power level calculated in step 5 is equal to or less than the reference value, the cutoff frequency correction method of the analog filter, characterized in that to maintain the current cutoff frequency of the analog signal.

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