JP2006165912A - Signal processor and image pickup device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a signal processor for accurately controlling a gain. <P>SOLUTION: In this audio signal processor 100, a variable gain amplifier 10 amplifies an analog audio signal SIG 12. An A/D converter 12 analog/digital converts an audio signal SIG 14 amplified by the variable gain amplifier 10. A gain control part 14 is configured of a digital circuit to control the gain of the variable gain amplifier 10 based on a digital audio signal SIG 16 to be outputted from the A/D converter 12. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a signal processing apparatus that adjusts a signal level of an analog input signal and converts the analog input signal into a digital output signal.

  A signal processing device that performs signal processing of an audio signal or the like includes an amplification unit that amplifies an input analog signal, and an analog-to-digital converter (hereinafter referred to as A / D conversion) that converts the analog signal amplified by the amplification unit into a digital signal. The signal converted into a digital signal by the A / D converter is output to a digital signal processor (Digital Signal Processor, hereinafter referred to as DSP) that performs various signal processing.

Here, when a signal having a wide dynamic range, such as audio, is handled, a technique is employed in which the gain of an amplifier that amplifies the input analog signal is changed in accordance with the amplitude of the input analog signal.
For example, Patent Document 1 discloses that when a signal level of an analog signal input to an A / D converter, that is, an amplitude is detected by a detection circuit and the detected signal level reaches a predetermined signal level, the analog signal is detected. A technique for controlling the signal level of an analog signal input to an A / D converter so as not to exceed a predetermined value by reducing the gain of an amplifier that amplifies the signal is disclosed.

JP-A-7-86943

  According to the technique described in FIG. 1 or FIG. 6 of Patent Document 1, the signal level of an analog input signal input to a signal processing device or an analog signal amplified by an amplifier is detected. Here, in order to detect the signal level of the analog signal, it is necessary to configure the detection circuit with an analog circuit. Therefore, when the element characteristics such as the resistance constituting the detection circuit vary, the detected signal level varies, and the accuracy of gain control of the amplifier may deteriorate.

  The present invention has been made in view of these problems, and an object thereof is to provide a signal processing apparatus capable of accurate gain control.

  In order to solve the above-described problems, a signal processing apparatus according to an aspect of the present invention includes a variable gain amplifier that amplifies an analog input signal, and an analog that converts the analog input signal amplified by the variable gain amplifier into a digital output signal. A digital converter; and a gain control unit that detects a signal level of the analog input signal based on a digital output signal output from the analog-digital converter and controls a gain of the variable gain amplifier.

  According to this aspect, the gain control unit detects the signal level of the digital output signal after digital conversion. Therefore, the gain of the variable gain amplifier can be accurately controlled even when variations in circuit element characteristics occur as compared with the case of detecting the signal level of an analog signal.

  The analog-digital converter may be a ΔΣ modulation type analog-digital converter including a ΔΣ modulator and a digital filter.

  The analog-to-digital converter includes a plurality of digital filters connected in multiple stages after the ΔΣ modulator, and the gain control unit converts the digital signal output from either the ΔΣ modulator or the plurality of digital filters connected in multiple stages. On the basis, the gain of the variable gain amplifier may be controlled.

  The gain control unit is connected to a ΔΣ modulator or multiple stages so that the delay time from when the analog input signal is input to the signal processing device until the signal level of the analog input signal is detected is less than the sampling cycle time of the analog input signal. The gain of the variable gain amplifier may be controlled based on a digital signal output from any of the plurality of digital filters.

  According to this aspect, the signal level of the digital signal output from the middle of the multiple digital filters connected in multiple stages is set so that the gain control timing of the variable gain amplifier is not delayed by the delay caused by the ΔΣ modulator and the digital filter. By detecting, the responsiveness of the signal processing device can be improved.

  The analog input signal input to the signal processing device may be an audio signal.

  Another embodiment of the present invention is also a signal processing device. This apparatus is a signal processing apparatus for analog-to-digital conversion of analog audio signals of a plurality of channels, and is amplified by a plurality of variable gain amplifiers that amplify the analog audio signals input for each channel and a plurality of variable gain amplifiers. A plurality of analog-digital converters for analog-digital conversion of the analog audio signals, and a gain control unit for controlling the gains of the plurality of variable gain amplifiers based on the plurality of digital signals output from the plurality of analog-digital converters. Prepare. The gain control unit reduces both the gains of the plurality of variable gain amplifiers when any one of the plurality of digital signals reaches a predetermined threshold value.

  According to this aspect, the gains of all the channels can be adjusted while performing the gain control of the variable gain amplifier based on the audio signal having the highest signal level among the audio signals input to the plurality of channels.

  Yet another embodiment of the present invention is an imaging apparatus. The apparatus includes an imaging unit, a microphone, the signal processing device that performs analog-digital conversion on an audio signal output from the microphone, and image data output from the imaging unit and an audio signal output from the signal processing device. And a digital signal processing unit.

  By mounting the above-mentioned signal processing device on an imaging device such as a digital still camera or digital video camera that can record audio signals, gain control is accurately performed according to the level signal of the input audio signal, and signal processing is performed. be able to.

  Note that any combination of the above-described constituent elements and the constituent elements and expressions of the present invention replaced with each other among methods, apparatuses, systems, etc. are also effective as an aspect of the present invention.

  According to the signal processing device of the present invention, accurate gain control can be performed according to the signal level of the input analog input signal.

(First embodiment)
FIG. 1 is a block diagram showing a configuration of an imaging apparatus 2000 according to the first embodiment of the present invention. The imaging device 2000 includes a microphone 200, an audio signal processing device 100, a DSP 300, and an imaging unit 310.

  The imaging unit 310 includes a lens, a CCD (Charge Coupled Device), and the like, converts video data into an electrical signal, performs analog-digital conversion, and outputs the signal to the DSP 300.

  The microphone 200 receives an audio signal AUD and converts it into an audio signal SIG10 that is an analog electric signal. The audio signal SIG10 converted into an electric signal by the microphone 200 is output to the audio signal processing apparatus 100.

  The audio signal processing apparatus 100 digitally converts the analog audio signal SIG10 and outputs a digital output signal SIG20 to the DSP 300.

  The DSP 300 records image data output from the imaging unit 310 and performs various signal processing such as format conversion and compression in order to record the digital output signal SIG20 output from the audio signal processing apparatus 100, or is not illustrated. Write data to the memory.

  FIG. 2 is a block diagram of the recording apparatus 1000 including the audio signal processing apparatus 100 and the peripheral circuit of FIG. The recording apparatus 1000 includes a microphone 200, an audio signal processing apparatus 100, and a DSP 300.

  The audio signal processing apparatus 100 includes an analog input terminal 102 and a digital output terminal 104 as input / output terminals, digitally converts an analog audio signal SIG10 input to the analog input terminal 102, and outputs the digital output signal SIG20 from the digital output terminal 104. Is output.

The audio signal processing apparatus 100 according to the present embodiment includes a variable gain amplifier 10, an A / D converter 12, a gain control unit 14, a preamplifier 16, and an interface unit 18.
An analog audio signal SIG10 input from the analog input terminal 102 is amplified by the preamplifier 16 and output to the variable gain amplifier 10 at the subsequent stage.

  The variable gain amplifier 10 further amplifies or attenuates the audio signal SIG12 amplified by the preamplifier 16 and outputs the amplified signal to the A / D converter 12 at the subsequent stage. The gain of the variable gain amplifier 10 is controlled according to the signal level of the audio signal input from the microphone 200.

The A / D converter 12 performs analog-to-digital conversion on the analog audio signal SIG14 output from the variable gain amplifier 10 and outputs a digital audio signal SIG16. For example, the A / D converter 12 performs analog-digital conversion with 16 bits and a sampling frequency fs of 48 kHz.
The audio signal SIG 16 output from the A / D converter 12 is input to the gain control unit 14 and the interface unit 18.

  The interface unit 18 converts the signal format of the digital audio signal SIG16 output from the A / D converter 12, and outputs the digital output signal SIG20 to the DSP 300.

  The gain control unit 14 detects the signal level of the analog audio signal SIG 14 input to the A / D converter 12 based on the digital audio signal SIG 16 subjected to analog-digital conversion output from the A / D converter 12. The gain of the variable gain amplifier 10 is controlled. The gain control unit 14 is configured as a digital circuit. The gain control unit 14 generates a gain control signal SIG22 based on the audio signal SIG16 and outputs it to the variable gain amplifier 10. That is, the gain control unit 14 has a function equivalent to detecting the signal level of the audio signal SIG 14 before analog-digital conversion output from the variable gain amplifier 10, and the digital audio that is the output of the A / D converter 12. This is done by detecting the signal SIG16.

  The gain control unit 14 detects the signal level of the audio signal SIG14 every sampling based on the audio signal SIG16. The gain control unit 14 reduces the gain of the variable gain amplifier 10 when the digital audio signal SIG 16 exceeds a predetermined value. For example, the gain control unit 14 reduces the gain of the variable gain amplifier 10 by 0.5 dB when the audio signal SIG16 reaches a half level of full scale. Hereinafter, an operation of reducing the gain of the variable gain amplifier 10 when the audio signal SIG16 reaches a predetermined level is referred to as an attack operation.

  Further, the gain control unit 14 controls the timing at which the gain of the variable gain amplifier 10 is lowered by an attack operation. In the present embodiment, the gain control unit 14 reduces the gain of the variable gain amplifier 10 by 0.5 dB within the time of the sampling cycle time Ts = 1 / fs given by the reciprocal of the sampling frequency fs.

When the attack operation by the gain control unit 14 continues, the gain of the variable gain amplifier 10 continues to decrease. Therefore, the gain control unit 14 performs a recovery operation in which the gain of the variable gain amplifier 10 is gradually increased on a time scale sufficiently longer than the sampling cycle time Ts.
For example, the gain control unit 14 increases the variable gain amplifier 10 by 0.5 dB in a time that is about 1000 times the sampling cycle time Ts = 1 / fs. In this way, by gradually increasing the gain of the variable gain amplifier 10 by the gain control unit 14, when the volume of the audio signal AUD is reduced after the gain is set low by the attack operation, an appropriate gain is obtained. Can be returned.

The operation of the recording apparatus 1000 configured as described above will be described.
FIG. 3 is a time chart showing how the gain control unit 14 performs gain control. In FIG. 3, the signal level of the audio signal SIG10 output from the microphone 200 is shown in the first row. The signal level of the audio signal SIG14 output from the variable gain amplifier 10 is shown in the second stage of FIG. The third stage of FIG. 3 shows the gain α of the variable gain amplifier 10.

At times T0 to T1, the volume of the audio signal AUD input to the microphone 200 increases, and the signal level of the audio signal SIG10 gradually increases. At times T0 to T1, the gain of the variable gain amplifier 10 is set to α1. Therefore, the signal level of the audio signal SIG14 increases with the audio signal SIG10.
When the signal level of the audio signal SIG14 reaches the threshold value SIGmax at time T1, the gain control unit 14 reduces the gain of the variable gain amplifier 10 by 0.5 dB by the gain control signal SIG22 and sets it to α2.

  As a result of the gain of the variable gain amplifier 10 being lowered at time T1, the signal level of the audio signal SIG14 is lowered. Since the signal level of the audio signal SIG10 continues to increase for a while after the time T1, the signal level of the audio signal SIG14 also increases with the increase of the signal level of the audio signal SIG10, and thereafter takes a substantially constant value.

  In this way, the gain control unit 14 monitors the digital audio signal SIG16 that is the output of the A / D converter 12, and when the audio signal SIG14 reaches the predetermined signal level SIGmax, the gain of the variable gain amplifier 10 is reduced. As a result, the audio signal SIG14, that is, the input signal of the A / D converter 12, can be prevented from exceeding a certain value. By preventing the signal level of the analog audio signal SIG14 output from the variable gain amplifier 10 before analog-digital conversion from exceeding a certain value, a signal having a predetermined signal level or higher is input to the A / D converter 12. Therefore, the dynamic range required for the A / D converter 12 can be narrowed.

FIG. 4 is a block diagram showing a configuration of the A / D converter 12 of FIG. The A / D converter 12 is a ΔΣ modulation type AD converter, and includes a ΔΣ modulator 20 and a digital filter 22.
The ΔΣ modulator 20 outputs a pulse signal obtained by digitally converting the input analog audio signal SIG14 by oversampling 64 times.
The digital filter 22 is a decimation filter for removing high-frequency components, and down-samples a signal that has been oversampled by 64 times and transmits the audio signal band. The digital filter 22 is composed of six digital filters 22a to 22f connected in series, and is downsampled to 1/2 times for each stage and output.

  In the A / D converter 12 configured as described above, a delay occurs in the ΔΣ modulator 20 and the digital filter 22. Assuming that the delay time in the ΔΣ modulator 20 is τ1, and the delay times in the digital filters 22a to 22f are τ2a to τ2f, respectively, the audio signal SIG16 output from the last stage digital filter 22f has a delay time τ with respect to the audio signal SIG14. = Τ1 + τ2a + τ2b + τ2c + τ2d + τ2e + τ2f

  The delay time τ is a time required for the audio signal SIG14 input to the ΔΣ modulator 20 to be converted from analog to digital and output as the audio signal SIG16a. When the delay time τ is long, the time required for the gain control unit 14 to detect the signal level of the audio signal SIG 16a and set the gain of the variable gain amplifier 10 becomes long, so that accurate gain setting becomes difficult.

Therefore, as shown in FIG. 4, in audio signal processing apparatus 100 according to the present embodiment, among digital filters 22a to 22f connected in multiple stages, gain control is performed on audio signal SIG16b output from intermediate stage digital filter 22d. The signal is output to the unit 14, and the gain level is controlled by detecting the signal level of the audio signal SIG16b.
Of the digital filters 22 connected in multiple stages, the audio signal output from which stage is output to the gain control unit 14 depends on the delay time of the ΔΣ modulator 20 and each of the digital filters 22a to 22f and the gain control unit 14. It may be determined based on the response speed required for the system.
For example, the delay time τ = τ1 + Στ2 may be set to be equal to or less than the sampling cycle time Ts.

  As described above, when a plurality of digital filters are connected in multiple stages, the gain control unit 14 monitors the output signal of the digital filter in the middle to shorten the delay time, and the signal level of the audio signal fluctuates rapidly. Even in this case, the gain control of the variable gain amplifier 10 can be followed.

  As described above, according to the audio signal processing apparatus 100 according to the present embodiment, the gain control unit 14 that controls the gain of the variable gain amplifier 10 is arranged in the subsequent stage of the A / D converter 12 and digitally converted. Based on the audio signal SIG16, the signal level of the audio signal SIG14 output from the variable gain amplifier 10 is detected. Therefore, the signal processing in the gain control unit 14 can be digitized and configured as a digital circuit. As a result, compared to the case where the gain control unit 14 is configured by an analog circuit, even when the characteristics of the transistors and resistors constituting the circuit vary, the detection of the signal level is not affected. The gain of the variable gain amplifier 10 can be set appropriately in accordance with the volume of the audio signal AUD input to.

  Further, by configuring the gain control unit 14 with a digital circuit, it becomes easy to set and change the gain control parameters of the variable gain amplifier 10. For example, the amount of decrease in the gain of the variable gain amplifier 10 by a single attack operation, the time required for the attack operation and the recovery operation, and the like can be freely changed in the digital circuit.

  In addition, since the variable gain amplifier 10 that performs amplification and attenuation is configured by an analog circuit, a high-performance A / D converter is not required, so that the circuit scale and current consumption can be suppressed.

(Second Embodiment)
FIG. 5 is a block diagram showing a configuration of a recording apparatus 1010 including a two-channel audio signal processing apparatus 110 and peripheral circuits according to the second embodiment. In FIG. 5, the same components as those in FIG. 2 are denoted by the same reference numerals, and redundant description is omitted.
The recording device 1010 supports stereo input, converts the audio signals SIG10R and SIG10L output from the two microphones 200R and 200L from analog to digital, and outputs them to the DSP 300.
The recording device 1010 includes two microphones 200R and 200L, an audio signal processing device 110, and a DSP 300.

The audio signal processing apparatus 110 includes a variable gain amplifier 10 and an A / D converter 12 that amplify an audio input signal for each of the R channel and the L channel. Each channel is distinguished by subscripts R and L.
Based on the audio signals SIG16R and SIG16L output from the A / D converters 12R and 12L of the respective channels, the gain control unit 14 determines the signal levels of the audio signals SIG14R and SIG14L input to the A / D converters 12R and 12L. Is detected. As a result, when one of the audio signals SIG14R and SIG14L reaches the threshold value SIGmax, the gain of the variable gain amplifiers 10R and 10L is reduced by 0.5 dB by the gain control signal SIG22. That is, in audio signal processing apparatus 110 according to the present embodiment, gain α of variable gain amplifiers 10R and 10L provided for each channel is controlled simultaneously.

According to the audio signal processing device 110 according to the present embodiment, even in an audio signal processing device having a plurality of channels such as stereo, the gain control unit 14 is configured by a digital circuit as in the first embodiment. be able to. As a result, compared to the case where the gain control unit 14 is configured by an analog circuit, even when characteristics such as transistors and resistors constituting the circuit vary, accurate amplitude detection can be performed. The gains of the variable gain amplifiers 10R and 10L can be appropriately set according to the volume of the audio signal AUD to be performed.
Furthermore, by configuring the gain control unit 14 with a digital circuit, it becomes easy to set and change the gain control parameters of the variable gain amplifiers 10R and 10L.

  Those skilled in the art will understand that the above-described embodiment is an exemplification, and that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there.

  In the present embodiment, the case where the A / D converter 12 is a ΔΣ modulation type A / D converter has been described. However, the present invention is not limited to this, and an A / D conversion such as a step flash type or a two step flash type is possible. A vessel may be used. In an A / D converter such as a step flash type, there is almost no delay, so the audio signal SIG 16 output from the A / D converter 12 can be input to the gain control unit 14.

  In the present embodiment, the case where the signal input to the signal processing device is an audio signal has been described. However, the present invention is not limited to this, and the present invention provides a signal processing device that converts an analog signal into an analog signal and outputs the signal. Can be widely applied.

  In the present embodiment, all of the audio signal processing apparatus 100 may be integrated, or a block that performs analog signal processing and a block that performs digital signal processing may be integrated separately. Which part is integrated may be determined by cost, occupied area, or the like.

It is a block diagram which shows the structure of the imaging device which concerns on 1st Embodiment. FIG. 2 is a block diagram of a recording device including the audio signal processing device of FIG. 1 and peripheral circuits. It is a time chart which shows the mode of the gain control in the gain control part of FIG. It is a block diagram which shows the structure of the A / D converter of FIG. It is a block diagram which shows the structure of the audio signal processing apparatus which concerns on 2nd Embodiment, and the recording device containing a peripheral circuit.

Explanation of symbols

  10 variable gain amplifiers, 12 A / D converters, 14 gain control units, 16 preamplifiers, 18 interface units, 20 ΔΣ modulators, 22 digital filters, 100 audio signal processing devices, 110 audio signal processing devices, 102 analog input terminals, 104 digital output terminal, 200 microphone, 300 DSP, 310 imaging unit, 1000 recording device, 1010 recording device.

Claims (7)

A variable gain amplifier for amplifying an analog input signal;
An analog-to-digital converter for analog-to-digital conversion of an analog input signal amplified by the variable gain amplifier into a digital output signal;
Based on the digital output signal output from the analog-digital converter, a signal level of the analog input signal is detected, and a gain control unit that controls the gain of the variable gain amplifier;
A signal processing apparatus comprising:   The signal processing apparatus according to claim 1, wherein the analog-digital converter is a ΔΣ modulation type analog-digital converter including a ΔΣ modulator and a digital filter. The analog-to-digital converter includes a plurality of digital filters connected in multiple stages after the ΔΣ modulator,
3. The gain control unit according to claim 2, wherein the gain control unit controls the gain of the variable gain amplifier based on a digital signal output from either the ΔΣ modulator or the plurality of digital filters connected in multiple stages. The signal processing apparatus as described.   The gain control unit is configured so that a delay time from when the analog input signal is input to the signal processing device until the signal level of the analog input signal is detected is equal to or less than a sampling cycle time of the analog input signal. The signal processing apparatus according to claim 3, wherein the gain of the variable gain amplifier is controlled based on a digital signal output from either a ΔΣ modulator or the plurality of digital filters connected in multiple stages.   The signal processing apparatus according to claim 1, wherein the analog input signal is an audio signal. A signal processing apparatus for analog-digital conversion of analog audio signals of a plurality of channels,
A plurality of variable gain amplifiers for amplifying analog audio signals input for each channel;
A plurality of analog-to-digital converters for analog-to-digital conversion of analog audio signals amplified by the plurality of variable gain amplifiers;
A gain control unit for controlling the gains of the plurality of variable gain amplifiers based on a plurality of digital signals output from the plurality of analog-digital converters;
The signal processing apparatus, wherein the gain control unit reduces the gains of the plurality of variable gain amplifiers together when a signal level of any of the plurality of digital signals reaches a predetermined threshold value. An imaging unit;
With a microphone,
The signal processing apparatus according to claim 5, wherein the audio signal output from the microphone is analog-digital converted and output;
A digital signal processing unit that processes image data output from the imaging unit and an audio signal output from the signal processing device;
An imaging apparatus comprising:

Images