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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
electronic circuit for acoustically reproducing an original signal, and more particularly to a digital
signal processing (DSP) for realizing a feedback loop using a digital power amplifier.
BACKGROUND OF THE INVENTION Conventional speakers are open loop transducers. The
output of a transducer is largely dependent on its physical properties and the environment in
which it works. It is often difficult to control physical properties and the environment. In
particular, they vary with temperature, age and other factors. As the physical characteristics
change depending on the environment, the sound to be reproduced will also change greatly from
the original signal.
Until now, special attention was needed in the design and manufacture of the transducer in order
to improve the transducer performance and maintain the transfer function linearity, ie the
relationship between the original signal and the output signal. Therefore, expensive materials,
precise assembly and special manufacturing techniques have been required. For example, it is
common practice to make the magnet larger and stronger to improve the performance of the
speaker transducer. However, doing so is expensive and greatly affects the size and weight of the
transducer package. The increase in size and weight is a problem, especially when mounted in a
In classical analog amplifiers used in known sound reproduction devices, the power gain is
dependent on the amplitude modulation of the DC power supply. However, these amplifiers are
inherently inefficient, with a typical efficiency of only about 50%. This results in high cost, but
requires a large heat sink to dissipate the energy loss, especially when the power level is high,
and because the power is used inefficiently, the reliability of the semiconductor is high. Because
the sex is low, the cost is high.
In the conventional digital power amplifier, the energy loss of power consumption is reduced by
using the conduction time modulation of the direct current source and the low loss switching
element. However, the control circuit of the conventional digital power amplifier is usually
composed of discrete semiconductor devices. These digital power amplifiers require expensive
high-speed analog circuits in which component placement and wiring lengths are severely
limited in order to avoid crosstalk. Such circuits are required to improve performance, and as the
amplifier bandwidth increases, placement restrictions become increasingly severe. As a result,
the configuration of these amplifiers becomes increasingly complex and very expensive to
perform accurate sound reproduction. Still, with digital systems, the efficiency goes up to 90%.
Another way to prevent the transducer from becoming expensive and heavy due to the use of
large magnets is to use dynamic feedback. In this type of system, in the examples disclosed in US
Pat. Nos. 4,180,706 and 3,647,969, the feedback signal is processed by conventional analog
power amplifiers and analog circuits to provide classical Feedback control. However, when using
analog hardware and control in this way, performance is likely to fluctuate due to component
variations and aging and environmental conditions. Therefore, it is complicated and expensive to
make and use this type of system, since the variation must be compensated by design and
component selection. When mounted in a car, size, weight, reliability and cost are very important
factors for mass production of the car. Furthermore, as the sound reproduction system becomes
more complex and less efficient, so much energy is consumed in the car's electrical system, so
more needs to be stored. Therefore, if a more powerful analog sound reproduction system, such
as an entertainment system or an active noise cancellation system, is made in the conventional
manner and mounted on a vehicle, the size and capacity of the power source such as a battery or
generator must be increased accordingly. . Similarly, a conventional broadband digital audio
reproduction system mounted on a car is limited in complexity and hardware, and the
improvement of the transducer is also accommodated in the car when the size of the magnet is
limited. It gets harder.
SUMMARY OF THE INVENTION The present invention overcomes the above-mentioned
drawbacks, and in a sound reproduction system according to the present invention, a digital
power amplifier (DSP) controlled digital power amplifier and motional feedback. And the signal
source drives the transducer. The digital power amplifier modulates the conduction time of the
DC power supply, and controls the ratio of on time to off time using a low loss switching element.
This improves efficiency and reduces power consumption as compared to analog amplifiers, and
the placement of discrete semiconductor components that make up a digital amplifier also
typically does not require strictness. Also, dynamic feedback detects the acoustic output of the
transducer and converts it to a digital signal. The DSP compares it to the digital representation of
the original input signal and generates a modified drive signal to supply to the transducer. This
feedback is performed in a classical negative feedback control system. Such feedback
compensates for non-linearities in the system due to transducer design, manufacturing
characteristics and operating environment, and solves design and component selection problems
in conventional dynamic feedback systems.
Preferably, the digital power amplifier and the dynamic feedback are integrally controlled by one
digital signal processor (DSP). Either analog input or digital input can be employed, but in the
case of analog input it is converted to binary code, so the DSP uses binary data strings to
calculate an appropriate error correction signal and To the transducer. The signal is converted
into a high speed pulse train and the duration of the pulse is responsible for the amplitude of the
loudspeaker signal. The pulse train then passes through the filter to remove unwanted high
frequency components and is supplied to the transducer.
Likewise, a motion sensor used for motional feedback produces a digital output or an analog
output. The analog output is converted to binary code. Additional features such as frequency and
phase equalization, power limiting, overload protection, dynamic range compression and
decompression can also be added to the DSP control system with little or no additional hardware.
Thus, according to the present invention, an improved acoustic response is obtained from the
speaker. This response may be more accurate and at a much lower cost than models that are
precisely designed and made according to the requirements of conventional high linearity
transducers. Also, the large or expensive magnet structures that are conventionally required for
accurate sound reproduction are substantially eliminated. Thus, the invention is particularly
suitable for use in mass production of motor vehicles, helping to reduce costs and ease of
installation limitations. The result will have a major impact on the product market. In addition,
high efficiency is achieved by using digital power amplifiers, reducing the need for expensive
heat sinks and reducing overall power consumption. As a result, unlike the prior art, it is possible
to add sound output enhancement and other improvements without adding parts therefor. Also,
the power consumption required to add these functions can be considerably reduced compared
to conventional analog systems, and the complexity is also reduced compared to digital
amplifiers built using discrete semiconductor devices.
Therefore, an advantage of the present invention is that it provides an acoustic speaker system
using a DSP controlled digital power amplifier and dynamic feedback. Another advantage of the
present invention is that the present invention provides a speaker system that can provide more
accurate sound reproduction at less cost and with smaller equipment than conventional
performance improvement techniques. Yet another advantage of the present invention is that a
loudspeaker system can be obtained that includes digital signal processing techniques without
adding to the cost of hardware and the associated implementation to realize the performance
improvement. Yet another advantage of the present invention is that it provides significantly
lower energy consumption and improved acoustic performance as compared to conventional
performance-enhancing implementations.
present invention will now be described with reference to the drawings. As shown in FIG. 1, the
sound reproduction system 10 includes a signal source 12, an amplification unit 14 and a
plurality of speakers 16. In the preferred embodiment, the system 10 is a conventional carmounted acoustic entertainment system and includes an auxiliary bass speaker system 20. The
auxiliary bass speaker system 20 includes the digital power amplifier and dynamic feedback
controller 22 of the present invention. However, the DSP amplifier and dynamic feedback
controller 22 may be used with the main amplification portion of the acoustic entertainment
system or in other automotive sound reproduction systems such as active noise silencers.
In the preferred embodiment, the role of the controller 22 in the auxiliary bass speaker system is
chosen to conventionally reproduce the most non-linear portion of the original signal. In addition,
the auxiliary bass speaker system is responsible for the lowest frequency portion of the spectrum
of sounds that is most relevant to the cone motion needed to provide accurate playback.
Therefore, precise engineering and placement of the largest possible magnet or transducer parts
is required to acoustically reproduce the original signal source. However, the present invention is
not limited to the frequency range of the auxiliary bass loudspeaker system in the preferred
As shown in FIG. 1, the auxiliary bass speaker system 20 includes a transducer 24 driven by a
controller 22. The control device 22 includes an interface unit 29, a DSP amplification unit 50,
and a dynamic feedback circuit 23. As shown in FIG. 2, when the system 20 is used in a
conventional car audio entertainment system, an analog input 17 is usually input. However,
digital signals originating from digital signal sources may be received directly by DSP controller
30, as shown by phantom line 19 in FIG. However, usually, the analog-to-digital converter 26
binary-codes the analog signal, and the converted digital signal is supplied to the DSP controller
30. The DSP controller 30 can be implemented with conventional hardware, such as, for example,
the Texas Instruments TMS320C25.
The DSP controller 30 is connected to a power amplifier including a pulse generator 32 via an
address bus, a control bus and a data bus. The pulse generator 32 is connected to the H bridge
circuit 33. The details of the DSP power amplifier 50 are shown in FIG. The output of the Hbridge 33 is preferably passed through a low pass filter 38 to remove unwanted high frequency
components such as digital carriers and then supplied to the speaker 24. Otherwise, unnecessary
high frequency components are reproduced by the speaker. If the speaker impedance is high
enough at the carrier frequency of the digital power amplifier and there is little current flow
through the speaker 24 and little energy dissipation, then the filter 38 may not be necessary.
As shown in more detail in FIG. 3, the pulse generator 32 comprises a set of positive data
registers and a pulse generating counter, and a set of negative data registers and a pulse
generating counter. The data supplied to the pulse generator 32 is output to the H bridge circuit
33 as a pulse width modulated (PWM) signal. The registers and counters are made with
conventional logic devices, but their circuit configuration is determined by the size (number of
bits) and speed of the words employed. In the H bridge circuit 33, two types of pulse width
modulated signals are input to the H bridge driver 34. The driver 34 comprises an isolated
switch driver such as Linear Technology's LT1158. Each switch driver provides positive and
negative signals to MOSFET transistors arranged in the form of a conventional H-bridge. For
example, this type of glitch can be made with four IRFZ44 MOSFET transistors. The load
connected to the central branch of the H bridge preferably passes through a low pass filter 38,
which removes the carrier and prevents excess energy from being dissipated in the speaker 24.
The hardware of the amplifier shown in FIG. 3 is shown in FIG. 4 with an additional DSP
controller implemented in software in DSP 30. Specifically, the software includes, for example, an
interface unit 29 including a filter and a scaling circuit 60 and a part of a protection circuit 72, a
part of a dynamic feedback circuit 23 including a dynamic feedback 70 and a part of a protection
circuit 72 And a portion of the amplifier 50 including the portion 80. The filter function acts
directly on the digital audio data to perform frequency crossover in the range acoustically
reproduced by the speaker 24. The scaling function sets the gain of the system, thereby
controlling the sound output level of the speaker 24. As shown in more detail in FIG. 5, the low
pass filter 62 and the gain control 64 may be added with a conventional frequency equalizer 66
such as software that performs the function of a digital filter.
As shown in FIG. 4, the dynamic feedback and associated protection unit 70 receives the signal
from the analog to digital converter 26, and the A / D converter 26 is attached to the speaker 24,
for example a transducer 27 such as an accelerometer. Receive a dynamic feedback signal from
Also, the output 88 of the amplifier feedback loop 81 surrounded by a virtual line in FIG. 4 is
input to the amplifier function circuit 80. Specifically, a clip detector as simple as a numerical
boundary algorithm can control the gain of the amplifier to prevent clipping.
Referring again to FIG. 5, dynamic feedback and associated protection 70 are shown in more
detail. The protection function 72 receives, for example, the output of the frequency
compensation unit 74, has a function of limiting thermal energy, and performs a filter function
necessary to keep the feedback loop stable by classical feedback control. Another preferred
example of the dynamic feedback protection function is to receive digital dynamic data signals
25 generated in response to the action of the feedback transducer 27 to limit the vibration
amplitude of the loudspeaker diaphragm. The output of protection function 72 is summed with
the digital data signal and adjusted by loop gain 76 to produce an appropriate output 78. The
output 78 is provided to an amplifier interface circuit 80.
As shown in more detail in FIG. 6, the digital speaker data 78 supplied to the amplifier function
circuit is processed and separated using the SIGNUM function, and data is supplied to the
positive pulse generator and the negative pulse generator of the amplifier 50. . An optional
feedback loop 81, also shown in FIG. 6, receives the output of the amplifier, and the feedback
signal is processed through loop filtering 82 and loop gain control 84. The loop filtering 82 of
this optional feedback loop 82 can also be employed in any desired manner, such as a nested
differential feedback loop.
As a result, the use of digitally processed signals results in significant energy savings as
compared to analog signal processing in conventional dynamic feedback systems. Also, using a
digital signal processing amplifier is very advantageous in terms of implementation as compared
to processing a signal digitally using a conventional analog amplifier and a high precision analog
circuit. The integrated DSP power amplifier with dynamic feedback disclosed herein consumes
much less power in the power output range of the amplifier as compared to a conventional
analog amplifier. Although partial, the DSP system of the present invention is much more
efficient than conventional analog amplifiers. Furthermore, DSP dynamic feedback systems are
more stable than systems using conventional hardware and components used in control. In
conventional systems, performance was likely to fluctuate due to component variations, aging
and environmental conditions.
While the invention has been described above, many modifications may be made by one skilled
in the art without departing from the spirit of the invention as set forth in the claims.
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