CN100417043C - Automatic gain controller and its control method - Google Patents

Abstract

The present invention relates to an automatic gain controller and a control method thereof. The automatic gain controller comprises a first multiplexer for receiving an input signal and a gain and generating a first output; a second multiplexer for receiving a signal time constant and a gain time constant and generating a second output; a filter electrically connected to the first multiplexer and the second multiplexer for generating a signal energy or an actual gain in response to the first output and the second output; and a signal energy processing device electrically connected to the filter and the first multiplexer and the second multiplexer for generating the gain and the gain time constant in response to the signal energy.

Description

Automatic gain controller and its control method

(1) Technical field

The invention relates to an automatic gain controller and its control method, in particular to an automatic gain controller with noise suppression function and its control method.

(2) Background technology

In general voice transmission equipment, such as Digital Enhanced Cordless Telecommunications (DECT), in order to eliminate echo, an echo canceller (echo canceller) is often built in. At the same time, in the hands-free (hand free) mobile phone, because the distance between the speaker's position and the mobile phone may change, resulting in the sound fluctuating, in order to control the volume within the preset range, the general voice transmission The devices all use an automatic gain controller for volume control.

Please refer to Fig. 1, it is the internal circuit block diagram of general speech transmission equipment, and it comprises an analog-to-digital converter (Anolog-to-Digital Converter, ADC) 11, a digital-to-analog converter (Digital-to-Anolog Converter, DAC ) 18, a finite impulse response filter (Finite ImpulseResponse Filter) 15, and an automatic gain controller (Automatic GainController, ADC) 13. After the analog signal input is converted into a digital signal by the analog-to-digital converter 11, the digital signal is multiplied by a first gain 12 and the echo value calculated by the finite impulse response filter 15 is subtracted to obtain a uniform Signal energy, the signal energy needs to be processed by the automatic gain controller 13 before being transmitted to the loudspeaker 14, so as to avoid the phenomenon that the sound heard by the receiver is fluctuating. When speaking, the signal received by the microphone 16 is multiplied by a second gain 17 , and converted into an analog signal by the digital-to-analog converter 18 for output.

Please refer to FIG. 2(a) and FIG. 2(b), which are the signal waveform diagrams before and after the volume is processed by the automatic gain controller used in the general voice transmission equipment. The waveform shown in Figure 2(a) is the measured waveform at point A in Figure 1, and the waveform shown in Figure 2(b) is the measured waveform at point B in Figure 1. It can be seen from Fig. 2(a) and Fig. 2(b) that the automatic gain controller will set two levels (Level) - the reference level (Assigned Level) and the noise level (Noise Level). The base level indicates the maximum preset volume, when the volume is higher than the base level, the automatic gain controller will reduce the volume. And when the volume is not greater than the reference layer, the automatic gain controller will amplify the volume, but will not amplify the volume to exceed the reference layer. As for the noise floor, it may be just noise when the volume is low, so it is not amplified.

However, in practical applications, when the first gain 12 and the second gain 17 are calculated by using a fixed point calculation, noise may be generated; in addition, the finite impulse response filter may not be able to remove the echo, and Noise with less energy remains. In the fixed-point calculation of these noises, if the number of bits is not enough, unpleasant noises may be generated, so it is necessary to further suppress the noises.

(3) Contents of the invention

The main purpose of the present invention is to provide an automatic gain controller, in the gain judgment process of the automatic gain controller, add the judgment to the noise floor, when the signal energy is not greater than the noise floor, provide a gain less than 1, make it To suppress noise.

According to one aspect of the present invention, there is provided an automatic gain controller, which includes: a first multiplexer, which has a signal enable terminal, and is set to a high level state for receiving a input signal and generate a first output; a second multiplexer, which has a signal enabling terminal, and which is set to a high level state, for receiving a signal time constant and generating a second output ; an infinite impulse response filter electrically connected to the first multiplexer and the second multiplexer for generating a signal energy in response to the first output and the second output; and a signal energy processing means, electrically connected to the infinite impulse response filter and the first multiplexer and the second multiplexer, for responding to the signal energy, and when the signal energy is greater than a predetermined noise floor, generate A first gain and a first gain time constant, and the first gain is fed back to the first multiplexer, the first gain time constant is fed back to the second multiplexer, and the first And the signal enable end of the second multiplexer is set to a low level state to output the first gain and the first gain time constant to the wireless impulse response filter, and then pass the wireless impulse response filter to obtain an actual gain, and when the signal energy is not greater than the noise floor, generate a second gain and a second gain time constant, and pass the second gain back to the first multiplexer and The second gain time constant is passed back to the second multiplexer, and then the signal enable terminals of the first and the second multiplexer are set to a low state to output the second The gain and the second gain time constant are sent to the infinite impulse response filter, and then passed through the infinite impulse response filter to obtain an actual gain.

According to the above idea, the input signal is a volume input signal.

According to the above idea, the filter uses two shift registers.

According to the above idea, when the first output is the input signal and the second output is the time constant of the signal, the filter outputs the signal energy.

According to the above idea, when the first output is the gain and the second output is the gain time constant, the filter outputs the actual gain.

According to the above idea, the signal energy processing device includes a comparator and a divider.

According to the above idea, wherein the signal energy processing device compares the signal energy with a preset noise floor, if the signal energy is greater than the noise floor, the signal energy processing device outputs a first gain and a first gain time constant; if the signal energy is not greater than the noise floor, the signal energy processing device outputs a second gain and a second gain time constant.

According to the above idea, the automatic gain controller further includes a multiplier electrically connected to the filter for multiplying the actual gain by the input signal to obtain an output signal.

According to the above idea, the automatic gain controller further includes a flip-flop electrically connected to the multiplier, and determines when to output the output signal according to its output enabling end.

According to the above idea, the flip-flop is a D-type flip-flop.

According to another aspect of the present invention, a method for controlling gain is provided, which is to process a signal energy through a signal energy processing device inside an automatic gain controller, and the automatic gain controller has a first and a second multi-channel converter, an infinite impulse response filter, a multiplier, and a D-type flip-flop, and generating an actual gain in response to the signal energy, the steps of which include: combining a signal from the first and the second multiplexers The enable terminal is set to a high level state; the infinite impulse response filter receives an input signal output by the first multiplexer, and receives a signal time constant output by the second multiplexer , and operate to generate the signal energy; compare the signal energy with a preset noise floor; if the signal energy is greater than the noise floor, the signal energy processing device generates a first gain and a first gain time constant; return the first gain to the first multiplexer, and return the first gain time constant to the second multiplexer; set the signal enable end to a low state; use the The first multiplexer outputs the first gain, and the second multiplexer outputs the first gain time constant, and transmits to the infinite impulse response filter; the first gain is processed by the infinite impulse response filter gain, and then obtain the actual gain; if the signal energy is not greater than the noise floor, the signal energy processing device outputs a second gain and a second gain time constant; returns the second gain to the first multiplexer device, and return the second gain time constant to the second multiplexer; set the signal enabling end to a low state; output the second gain with the first multiplexer, and Outputting the second gain time constant with the second multiplexer and sending it to the infinite impulse response filter; processing the second gain through the infinite impulse response filter to obtain the actual gain; using the multiplier to The actual gain is multiplied by the first output to obtain an output signal; an output enable end of the D-type flip-flop is set to a high level state; and the output signal is received by the D-type flip-flop, to send out the output signal.

According to the above idea, the signal energy processing device includes a comparator and a divider.

According to the above idea, the first gain is a value obtained by dividing a preset reference layer by the signal energy.

According to the above idea, the filter is a low-pass filter.

According to the above idea, the filter uses two shift registers.

According to the above idea, the second gain is a preset value not greater than 1.

(4) Description of drawings

FIG. 1 is a block diagram of an internal circuit of a general voice transmission device.

FIG. 2( a ) is a signal waveform diagram before the volume is processed by an automatic gain controller used in a general voice transmission device.

FIG. 2( b ) is a signal waveform diagram after volume is processed by an automatic gain controller used in a general voice transmission device.

Fig. 3(a) is a signal waveform diagram before the volume is processed by the automatic gain controller of the present invention.

Fig. 3(b) is a signal waveform diagram after the volume is processed by the automatic gain controller of the present invention.

Fig. 4 is a judgment flow chart of a preferred embodiment of the present invention.

FIG. 5 is a circuit block diagram of a preferred embodiment of the present invention.

FIG. 6 is a structural diagram of the infinite impulse response filter used in FIG. 5 .

(5) specific implementation

Please refer to FIG. 3( a ) and FIG. 3( b ), which are signal waveform diagrams before volume processing and signal waveform diagrams after volume processing by the automatic gain controller of the present invention. As can be seen from Figure 3(a) and Figure 3(b), the automatic gain controller can set two levels (Level) - the reference level (Assigned Level) and the noise level (NoiseLevel). The base level indicates the maximum preset volume, when the volume is higher than the base level, the automatic gain controller will reduce the volume. And when the volume is not greater than the reference layer, the automatic gain controller will amplify the volume, but will not amplify the volume to exceed the reference layer. As for when the volume is not greater than the noise floor, the volume will be lowered to achieve the purpose of suppressing noise, which is also the difference between the present invention and the prior art.

Please refer to FIG. 4 , which is a judgment flow chart of a preferred embodiment of the present invention. In order to achieve the purpose of suppressing noise, the present invention compares a signal energy (signal_energy) converted from volume with the noise floor (step 41), if the signal energy is greater than the noise floor, a first gain and A first time constant (step 42), then the first gain and the first time constant are processed by a low-pass filter (LowPass Filter) to obtain an actual gain (step 43); otherwise, if the signal energy is not greater than the noise floor, then produce a second gain and a second time constant (step 44), then process the second gain and the second time constant through the low-pass filter to obtain an actual gain (step 44) 45). Among them, the low-pass filter is used to adjust the gain, so that the gain does not change too fast.

The above-mentioned first gain is the value obtained by dividing the reference layer by the signal energy, the second gain is a preset value not greater than 1, and the related calculation formula is as follows (the formula (1) is the signal energy, formula (2) is the actual gain obtained when the signal energy is greater than the noise floor, and formula (3) is the actual gain obtained when the signal energy is not greater than the noise floor):

signal_energy[n]=signal_energy[n-1]+|signal|*2 ^{_signal_time_const} (1)

-signal_energy[n-1]*2 ^{-signal_time_const}

actual_gain[n]=actual_gain[n-1]+|Gain|*2 ^{_AGC_time_const1} (2)

-actual_gain[n-1]*2 ^{-AGC_time_const1}

actual_gain[n]=actual_gain[n-1]+|Gain|*2 ^{_AGC_time_const2} (3)

-actual_gain[n-1]*2 ^{-AGC_time_const2}

The purpose of choosing different time constants (AGC_time_const1 and AGC_time_const2) in formula (2) and formula (3) is mainly to allow users to set themselves according to system requirements to achieve different gain convergence speeds.

Please refer to Fig. 5, which is a circuit block diagram of a preferred embodiment of the present invention, the structure of this circuit block diagram is designed according to the judgment flow of Fig. 4, and it comprises a first multiplexer 51, a second multiplexer Road converter 52, an infinite impulse response filter (Infinite Impulse Response Filter) 53, a signal energy processing device 54, a multiplier 55, and a D-type flip-flop 56.

At the beginning, a signal connected to the first multiplexer 51 and the second multiplexer 52 is enabled to be set to a high level state ("1"). At this time, the first multiplexer 51 outputs an input signal (the first output) and the second multiplexer 52 outputs a signal time constant (the second output), and the input signal and the signal time constant are sent to the infinite impulse response filter 53 for calculation Generate a signal energy, and then send the signal energy to the signal energy processing device 54 for processing, wherein the signal energy processing device includes a comparator and a divider). The system will preset a noise floor, and if the signal energy is greater than the noise floor at this time, the signal energy processing device 54 outputs the first gain and the first gain time constant, and the first gain and the first gain The time constant is passed back to the first multiplexer 51 and the second multiplexer 52 for subsequent actual gain calculation; and if the signal energy is not greater than the noise floor, the signal energy processing device 54 outputs the second gain and the second gain time constant, and return the second gain and the second gain time constant to the first multiplexer 51 and the second multiplexer 52 for subsequent actual gain operation.

Then, the signal enable is set to a low level state ("0"), at this time the first multiplexer 51 outputs a gain (first gain or second gain) and the second multiplexer 51 outputs 52 outputs a gain signal time constant (the first gain time constant or the second gain time constant), the gain and the gain signal time constant are sent to the infinite impulse response filter 53 for calculation to generate an actual gain, and then through the multiplication The converter 55 multiplies the actual gain with the input signal to obtain an output signal. Finally, the output enable of the D-type flip-flop 56 is set to a high level state (“1”) to send out the output signal.

The infinite impulse response filter 53 used in Fig. 5 is the usefulness of calculation formula (1), (2) and (3), because formula (1), (2) and (3) are all 2 order square operation, so it can be implemented by a shift register. The structure diagram of the infinite impulse response filter is shown in Figure 6, which includes a first shift register 62, a second shift register 63, a fetch An absolute value operation 61 and an addition and subtraction operation 64 . Now take formula (1) as an example, and then refer to Figure 5, assuming that the first output is the input signal (signal), and the second output is the signal time constant (signal_time_const), then A, B, and C are obtained respectively as follows:

A＝|signal|*2 ^{-signal_time_const}

B=signal_energy[n-1]*2 ^{-signal_time_const}

C = signal_energy[n-1]

After calculating A, B, and C, perform the addition and subtraction operations to obtain the signal energy (signal_energy), and the results are as follows:

signal_energy[n]=A-B+C=signal_energy[n-1]+|signal|* ^{2_signal_time_comst}

-signal_energy[n-1]*2 ^{-signal_time_const}

According to the above principle, when the first output is the gain and the second output is the gain time constant, the actual gain can also be obtained through the infinite impulse response filter 53 .

In summary, the present invention has the following advantages compared to the prior art:

1. In the gain judgment process of the automatic gain controller, the present invention adds the judgment of the noise floor, and provides a gain less than 1 when the signal energy is not greater than the noise floor, so as to achieve the purpose of suppressing noise.

2. The present invention provides different gain time constants for the first gain and the second gain, so that the system can have different gain convergence speeds according to requirements during operation.

3. On hardware structure, the present invention has only used several simple circuit components, can finish the function of automatic gain controller and suppression noise, and there is no multiplier in the infinite impulse response filter that the present invention uses, Instead, it is replaced by a shift register, which greatly simplifies the hardware design and reduces the manufacturing cost.

The effects produced by the unique framework of the present invention are sufficient to effectively improve the deficiencies of the prior art, and thus have industrial value, thereby achieving the purpose of developing the present invention.

Claims (8)

1. An automatic gain controller comprising: A first multiplexer, which has a signal enabling terminal, and is set to a high level state, for receiving an input signal and generating a first output; a second multiplexer, which shares the signal enable terminal with the first multiplexer, and is set to a high level state, for receiving a signal time constant and generating a second output; an infinite impulse response filter electrically connected to the first multiplexer and the second multiplexer for generating a signal energy in response to the first output and the second output; and a signal energy processing device, electrically connected to the infinite impulse response filter and the first multiplexer and the second multiplexer, for responding to the signal energy, and when the signal energy is greater than a preset noise When layering, a first gain and a first gain time constant are generated, and the first gain is passed back to the first multiplexer, and the first gain time constant is passed back to the second multiplexer, and then setting the signal enabling end shared by the first and the second multiplexer to a low level state, so as to output the first gain and the first gain time constant to the wireless impulse response filter, and then An actual gain is obtained through the wireless impulse response filter, and when the signal energy is not greater than the noise floor, a second gain and a second gain time constant are generated, and the second gain is returned to the first The multiplexer and the second gain time constant are passed back to the second multiplexer, and then the signal enabling end shared by the first and the second multiplexer is set to a low level state , so as to output the second gain and the second gain time constant to the infinite impulse response filter, and then pass through the infinite impulse response filter to obtain an actual gain. 2. The automatic gain controller as claimed in claim 1, wherein the input signal is a volume input signal. 3. The automatic gain controller as claimed in claim 1, wherein the infinite impulse response filter uses two shift registers. 4. automatic gain controller as claimed in claim 1, is characterized in that, The signal energy processing device includes a comparator and a divider. 5. automatic gain controller as claimed in claim 1 is characterized in that, also comprises: A multiplier, electrically connected to the filter, for multiplying the actual gain with the input signal to obtain an output signal; a flip-flop, electrically connected to the multiplier, to determine what When the output signal is output, the flip-flop is a D-type flip-flop. 6. A method for controlling gain, which is to process a signal energy through a signal energy processing device inside an automatic gain controller, and the automatic gain controller has a first and a second multiplexer, an infinite An impulse response filter, a multiplier and a D-type flip-flop, and generating an actual gain in response to the signal energy, the steps comprising: setting a signal enable terminal shared by the first and the second multiplexer to a high level state; receiving an input signal output by the first multiplexer and a signal time constant output by the second multiplexer with the infinite impulse response filter, and performing operations to generate the signal energy; comparing the signal energy with a predetermined noise floor; If the signal energy is greater than the noise floor, the signal energy processing device generates a first gain and a first gain time constant; returning the first gain to the first multiplexer, and returning the first gain time constant to the second multiplexer; setting the signal enabling end shared by the first and second multiplexers to a low level state; outputting the first gain by the first multiplexer, and outputting the first gain time constant by the second multiplexer, and transmitting to the infinite impulse response filter; processing the first gain through the infinite impulse response filter to obtain the actual gain; If the signal energy is not greater than the noise floor, the signal energy processing device outputs a second gain and a second gain time constant; returning the second gain to the first multiplexer, and returning the second gain time constant to the second multiplexer; setting the signal enabling end shared by the first and second multiplexers to a low level state; outputting the second gain by the first multiplexer, and outputting the second gain time constant by the second multiplexer, and transmitting to the infinite impulse response filter; processing the second gain through the infinite impulse response filter to obtain the actual gain; multiplying the actual gain with the first output by the multiplier to obtain an output signal; an output enabling end of the D-type flip-flop is set to a high level state; and The output signal is received by the D-type flip-flop to send out the output signal. 7. The method according to claim 6, characterized in that: The first gain is a value obtained by dividing a preset reference layer by the signal energy; The second gain is a preset value not greater than 1. 8. The method of claim 6, wherein: The infinite impulse response filter is a low-pass filter using two shift registers.

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