JP2009089340A - Production technology for negative impedance employing dc feedback circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve, at very low cost, improvement in the heavy low-pitched sound reproduction of a speaker, and traceability of an optical pickup. <P>SOLUTION: An inverse integration type DC feedback circuit 3 is combined with a differential amplifier, of which the naked gain in a low frequency domain is designed to be very large, or with a constant-voltage amplifier, having similar phase rotation around the minimum resonance frequency. Since the properties as an induced load become actual, by increasing the mechanical impedance around the minimum resonance frequency of a speaker or of an optical pickup, the voltage phase of constant-voltage amplifier output is delayed. In the inverse integration type DC feedback circuit 3, the voltage phase in the cutoff frequency or higher is led by about at 90°, so that positive feedback becomes possible, by setting the cutoff frequency around the minimum resonance frequency of the speaker or of the optical pickup. By setting a DC feedback amount to a suitable value, amplifier operation around the minimum resonance frequency is made similar to that of a constant-current amplifier, and reduction compensation of reproduced sound pressure or improvement in traceability are realized. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to an electroacoustic device and an electronic control device, and more particularly, to a negative impedance generator and method necessary for suppressing a minimum resonance frequency generated when a speaker and an optical pickup are driven.

At the lowest resonance frequency of the speaker, the drive impedance is lowered, so that the electrical impedance rises and Q point is generated (FIG. 6). The impedance rise at the lowest resonance frequency is around 60Ω for a speaker with a rating of 8Ω. Since the speaker is generally driven at a constant voltage, the reproduced sound pressure around the lowest resonance frequency is reduced to about one-eighth of the reproduced sound pressure generated in the rated impedance region.

A tone control circuit and an equalizer unit have been used for a long time as a method for improving the reproduction sound pressure drop around the lowest resonance frequency by manipulating the frequency characteristic of the input acoustic signal. Although it is not necessary to use a special power amplifier and it is convenient, the number of amplification stages through which the acoustic signal passes increases, so that the sound quality changes and the characteristics deteriorate. In addition, the bass range of the input sound signal is increased, so that the howling margin, which is the difference between the playback level at which howling occurs and the actual playback level, is reduced, and the dynamic range is reduced by increasing the level around the lowest resonance frequency. Therefore, the high fidelity reproduction tends to be avoided.

As a technique to improve the reproduction sound pressure drop around the lowest resonance frequency without manipulating the frequency characteristics of the input acoustic signal, non-linear operation of the speaker is detected by a sensor coil provided in the microphone or voice coil, and negative feedback to the amplifier Thus, the MFB method (Motion Feed Back) for improving characteristics is put into practical use and widely known.

As a technique for improving the reproduction sound pressure drop around the lowest resonance frequency without manipulating the frequency characteristic of the input acoustic signal, a method of improving the characteristic by driving the speaker at a constant current is widely known.

A method of correcting only the load impedance viewed from the amplifier without compensating for a decrease in reproduced sound pressure around the lowest resonance frequency has been devised and well known (FIG. 5).

Since the actuator in the optical pickup used in the optical disk type reproducing apparatus and recording / reproducing apparatus has a similar structure to the speaker, a Q point is generated at the lowest resonance frequency.

Traceability degradation due to Q point is within the range that can be suppressed in the servo loop, but apparent Q point frequency degradation and support of moving parts that occur when the disk is rotated at high speed for high-speed access and high-density recording / reproduction. When an actuator using a metal leaf spring (common name: micro n-axis) is used, the low-frequency equivalent correction is performed because the traceability degradation cannot be ignored.

Considering the linearity of the servo loop, the error signal drive circuit has the best linear characteristics, and the frequency enhancement for equivalent correction is the nonlinear response amount of the servo loop (drive) when a transient excessive error signal is input. The adverse effect of this low-frequency equivalent correction, which increases the output time of the circuit and lengthens the convergence time of the servo loop, is similar to the correction by digital signal processing. Further, even in actuators other than the micro n-axis structure, suppression of the Q point leads to further improvement of traceability.

For this reason, some of the actuator drive ICs of some manufacturers have been announced to perform constant current drive of the load. However, since the output line of the driving IC has a high resistance, there is a problem in stability, and a general driving circuit is mainly driven at a constant voltage as in the case of a speaker. The use of a constant current amplifier in a speaker is also the same, and has been studied for a long time, but it has not been generalized due to problems such as a decrease in braking rate and stability.

The negative impedance is a concept used in an oscillation circuit or the like, and is an impedance component generated by controlling the load resistance value and the drive current value to have a proportional relationship.

In an acoustic amplifier, a high braking rate is regarded as a measure of performance. However, the braking rate when the constant current amplifier is used is extremely low in its operation. In the case of an MFB amplifier, it is common to implement it by adding a dedicated circuit to the constant voltage amplifier. In this case, although the braking rate is improved, the circuit scale becomes larger than that of a normal constant voltage amplifier. It is also disadvantageous in terms of stability.

In an optical pickup actuator, suppression of the Q point is important in order to improve traceability. However, when a constant current amplifier or MFB is used, a problem similar to that at the time of suppression of the Q point of the speaker occurs. Similar to the use of a tone control circuit or an equalizer unit in a speaker, the low-frequency equivalent correction also causes a decrease in the dynamic range in the servo loop.

The present invention is a high-feedback constant voltage power amplifier that is generally used and a high braking rate that is a feature of the constant voltage amplifier by reexamining the constants of the DC feedback circuit used for removing the output offset voltage. The basic principle is to compensate for a decrease in power conversion efficiency around the Q point of the speaker or optical pickup without lowering.

As an advanced form, the same compensation results can be achieved even in constant voltage power amplifiers, digital amplifiers, and actuator drive ICs that do not perform overall negative feedback. High-quality acoustic amplifiers capable of reproducing deep bass and high-traceability optics Disc-type playback equipment and recording / playback equipment are provided at low cost.

As means for compensating for a decrease in reproduced sound pressure around the lowest resonance frequency of a speaker according to a conventional technique, use of a constant current amplifier, use of MFB, use of a tone control circuit and an equalizer unit are generally used.

The reproduction sound pressure obtained by using the constant current amplifier is the reverse characteristic of the constant voltage amplifier. Therefore, even if the decrease in the reproduction sound pressure at the lowest resonance frequency can be compensated, the total reproduction frequency characteristic is the characteristic expected when designing the speaker. For this purpose, it is common to use a dedicated equalizer for frequency characteristic compensation. In addition, it is said that there is much discomfort in terms of hearing because the braking rate is extremely lower than that of a constant voltage amplifier.

Although the use of MFB is prevalent mainly in subwoofers, it is common that the structure becomes complicated and that there is also a sense of incongruity in hearing and that a dedicated equalizer is also used. The above problem is exactly the same when the actuator of the optical pickup is driven.

The present invention actively utilizes the phase rotation problem inherent in the differential amplifier using the overall negative feedback, thereby maintaining the wideband and high braking rate characteristic of the constant voltage amplifier, The reproduction sound pressure drop and the driving force drop in the vicinity of the lowest resonance frequency of the optical pickup are effectively compensated. Further, in a constant voltage power amplifier or digital amplifier that does not perform overall negative feedback, the same effect is realized by setting the phase delay around the lowest resonance frequency to around 90 degrees by using the phase shifter (21). .

The basic configuration for all applications is shown in FIG. 1 and is the best mode. If the circuit 2 and the circuit 3 have a sufficient bare gain and a sufficiently stable design, they can be used for any speaker driving circuit. New circuit operation is added only by changing the constants of the conventional circuit, so it can be realized at low cost and in small size, but high-quality heavy bass reproduction can be realized extremely stably. It is expected to be used for equipment.

The actuator drive IC often determines the gain of the drive IC at the time of design. Therefore, the amount of phase rotation is not fixed by the actuator drive IC used. Therefore, the use of FIG. 13 or FIG. 14 is determined by actual measurement when the optical pickup is driven. In application to optical pickup, the traceability improvement at defect and lead-in is great, and as a result, the system can be made highly efficient, so it is expected to be applied to all optical disc type reproduction equipment and recording / reproduction equipment. .

In the example of FIG. 1, a phase inverter (1) that compensates for phase inversion in the circuit 2, an inversion type constant voltage power amplifier (2) that generates drive power, and an inversion integration type that eliminates an output offset voltage generated in the power amplifier. It consists of a DC feedback circuit (3). The inverting constant voltage power amplifier (2) is designed as a differential amplifier having a sufficiently large bare gain, and does not use the capacitive load compensation circuit (11) or the inductive load compensation circuit (12) shown in FIG. And a circuit configuration having a phase margin capable of stably driving an inductive load, and a gain is set by using an overall negative feedback.

A differential amplifier that is designed stably and that uses overall negative feedback absorbs the phase difference between the output current and the output voltage and controls the output voltage to be in phase with the input voltage. In actual differential amplifiers, when inductive or capacitive loads are driven due to problems of phase margin and gain margin associated with the circuit configuration, a phase difference occurs within the amplifier's phase margin range depending on the value. It will be a thing.

FIG. 11 shows a circuit used for the confirmation experiment as the inverting constant voltage power amplifier (2). When the loads 5 and 5A are driven using this circuit, the amplitude and phase of the drive current around the lowest resonance frequency are as shown in FIG. 7, and the load is a simplified equivalent circuit of the speaker as compared with the load 5A which is a pure resistance load. 5 confirms that the regenerative power, which is the product of current and voltage, decreases.

The cutoff frequency of the inverting integration type DC feedback circuit (3) for removing the output offset voltage is set to a frequency (usually 1 Hz or less) sufficiently lower than 20 Hz, which is generally regarded as the lower limit audible sound. The voltage phase between point D and point C when the cutoff frequency of the inverting integral type DC feedback circuit (3) is set around the lowest resonance frequency of the speaker in the circuit configuration of FIG. 2 is as shown in FIG. Therefore, since the feedback path is closed in FIG. 1 under the same conditions, the voltage phase between the point A and the point B is equivalent to the same phase state as shown in FIG. 9, and positive feedback is established.

Usually, R1 and R2 constitute a voltage divider that stabilizes the convergence of the DC feedback. When the bare gain of the circuit 3 is sufficiently large, the divided value is generally equal to or less than the inverse of the gain of the circuit 2. In FIG. 1, R1 and R2 are also used to adjust the positive feedback amount.

The frequency at which the positive feedback is established is equal to or higher than the cutoff frequency of the circuit 3, and the positive feedback component at that time is attenuated by about 10 dB as shown in FIG. Accordingly, the positive feedback amount is less than 1, and it can be understood that the circuit configuration of FIG. 1 operates similarly to the constant current amplifier (FIG. 10) without oscillation.

When driving the actuator of the optical pickup, the Q point can be lowered by using the circuits of FIGS. Actuator drive IC often determines the gain of the drive IC at the time of design, and the amount of phase rotation varies depending on the product, so the Q loop is in a state where the servo loop is disconnected (the phase rotation is absorbed when the servo is locked) When the output voltage is delayed by 90 degrees or more, FIG. 13 is used, and when the output voltage is delayed by less than 90 degrees, FIG. 14 is used.

The optical pickup may require a servo band from DC transiently, and lead-in and focus jump may be disabled by the DC feedback circuit. Therefore, in FIG. 13 and FIG. 14, the circuit 23 can stop DC feedback. It is said. The circuit 24 is a driving IC, and in many cases is a single power supply operation, but the positive / negative power supply operation notation is used to simplify the entire drawing. The circuit 25 is an addition resistor that reduces interference between the output of the circuit 3 and an error signal, and the circuit 26 is a simple expression of an optical pickup. FIGS. 1 and 12 show examples when the speaker is driven, and FIGS. 13 and 14 show examples when the optical pickup is driven.

Further, the sound quality control by varying the braking rate as in claims 2 and 4 is adopted in a commercial product under the name of damping factor control, and is a well-known effect among enthusiasts. The fact that the operating current in the servo circuit as in Item 8 affects the audio circuit and the video circuit is also well known among enthusiasts. Changes in glossiness and stickiness are known as the influence on the sound quality by the servo circuit, and good color and distortion of the screen are known as changes in the image.

The present invention has been developed as a technique for compensating for a decrease in power conversion efficiency around the Q point generated at the lowest resonance frequency of a speaker, and its application to an optical pickup has been confirmed as its development form.

However, it is possible to stably supply a signal having a bandwidth equal to or lower than the cutoff frequency of the DC feedback circuit to the load while compensating for a decrease in power conversion efficiency around the Q point by controlling cutoff of the DC feedback in application confirmation to the optical pickup. It was confirmed.

Therefore, it seems possible to use it effectively for high-efficiency driving of all inductive loads, especially for robot control and electromagnetic solenoid control.

It is an Example of this invention. In the configuration of FIG. 1, the circuit 5 as a load is changed. It is a block diagram notation of FIG. It is a structural example of a general amplifier. It is an example of a compensation circuit that cancels out an increase in impedance around the lowest resonance frequency. This is an example of speaker impedance increase due to the lowest resonance frequency. This is a comparative example of the speaker drive current around the lowest resonance frequency and the drive current at the time of pure resistance load. This is a phase difference that occurs at a frequency equal to or higher than the cutoff frequency of the inverting integral type DC feedback circuit (3). It is an example of delay phase cancellation of an inverting integral type DC feedback circuit (3). 2 is a configuration example of a constant current power amplifier of a load current feedback type. It is a detailed view of an inverting constant voltage power amplifier (2) and an inverting integral type DC feedback circuit used for characteristic confirmation. This is an application example when the phase relationship of FIG. 9 is not established, such as a digital amplifier or an amplifier that does not perform overall negative feedback. This is an application example when a delay of 90 degrees or more occurs in the output voltage when the optical pickup is driven at Q point. This is an application example when a delay of less than 90 degrees occurs in the output voltage when the optical pickup is driven at the Q point.

Explanation of symbols

1 Phase inverter 2 Inverted constant voltage power amplifier (power amplifier)
3 Inverting Integral Type DC Feedback Circuit 4 Speaker Terminal 5 Speaker Simplified Equivalent Circuit 5A Pure Resistive Load 6 Phase Inverter Block Diagram Notation 7 Inverting Constant Voltage Power Amplifier (Power Amplifier) Block Diagram Notation 8 Speaker Terminal Block Diagram Notation 9 Block diagram notation of simplified speaker equivalent circuit 10 Block diagram notation of inverting integration type DC feedback circuit 11 Capacitive load compensation circuit 12 Inductive load compensation circuit 13 Minimum resonance frequency impedance correction circuit 14 Minimum resonance frequency of circuit 5 is input to FIG. Current waveform 15 flowing through the circuit 5A when the lowest resonance frequency of the circuit 5 is input to FIG. 1, current waveform 16 flowing through the circuit 5 FIG. 2, waveform C at the point 17 FIG. 2, waveform D at the point 18 lowest resonance of the circuit 5 The frequency A point waveform 19 at the time of input in FIG. 1 The lowest resonance frequency of the circuit 5 at the point B waveform 20 at the time of input in FIG. Vessel 22 digital amplifier or the like effective band switching circuit 24 actuator drive IC of the servo loop by the constant voltage amplifier 23 DC feedback ON / OFF is not performed overall negative feedback (power driver IC)
25 Adder resistor 26 to reduce error signal interference 26 Optical pickup A The minimum resonance frequency of the circuit 5 is the output of the circuit 3 at the time of input B. The minimum resonance frequency of the circuit 5 is the output of the circuit 2 at the input of FIG. 2 is the circuit 2 output D at the time of input in FIG. 2 The circuit 3 output R1 at the time of input in FIG. 2 is the circuit 3 output R1 The ground resistance R2 of the DC feedback circuit The feedback resistance R3 of the DC feedback circuit The pure resistance of the speaker Component R4 Rated impedance value of the speaker

Claims (8)

As a result of using the circuit configuration of FIG. 1, it is characterized by correcting the decrease in the reproduced sound pressure near the lowest resonance frequency of the speaker while maintaining the high braking rate that is characteristic of the constant voltage power amplifier. Audio equipment additional circuit and device to perform. A constant voltage power amplifier realized as a result of using the circuit configuration according to claim 1, wherein the sound quality to be reproduced is changed by changing a braking rate in a low sound region when the speaker is driven. And equipment. As a result of using the circuit configuration of FIG. 12, the reproduced sound pressure drop near the lowest resonance frequency of the speaker is extremely stable while maintaining the characteristic sound quality of constant voltage power amplifiers and digital amplifiers that do not perform overall negative feedback. An audio equipment additional circuit and device characterized by correcting the above. A constant voltage power amplifier realized as a result of using the circuit configuration according to claim 3, wherein the sound quality to be reproduced is changed by changing a braking rate in a low sound region when the speaker is driven. And equipment. As a result of using the circuit configuration of FIG. 13, the servo at the time of transient excessive error signal input is improved by improving the traceability in the vicinity of the lowest resonance frequency of the optical pickup and by reducing the low frequency equivalent correction amount of the servo circuit. An optical pickup additional circuit and device characterized in that the nonlinear response amount of the loop is reduced and the convergence of the servo loop is accelerated. As a result of using the circuit configuration of FIG. 14, the servo at the time of transient excessive error signal input is improved by improving the traceability near the lowest resonance frequency of the optical pickup and by reducing the low-frequency equivalent correction amount of the servo circuit. An optical pickup additional circuit and device characterized in that the nonlinear response amount of the loop is reduced and the convergence of the servo loop is accelerated. The servo circuit using the circuit configuration of FIG. 13 is used to vary the braking rate in the low range when driving an actuator such as a focus coil, tracking coil, tilt coil, etc., and the current mode flowing to the servo circuit and the current mode flowing to the power circuit Optical disk playback equipment and recording / playback equipment characterized by giving subtle changes to the sound quality and image quality of recording and playback when changed. The servo mode using the circuit configuration of FIG. 14 is used to vary the braking rate in the low range when driving an actuator such as a focus coil, tracking coil, tilt coil, etc., and the current mode that flows to the servo circuit and the current mode that flows to the power circuit Optical disk playback equipment and recording / playback equipment characterized by giving subtle changes to the sound quality and image quality of recording and playback when changed.

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