RU2281607C2 - Method and hybrid amplifier for amplifying digital signals - Google Patents

Abstract

FIELD: amplifying engineering; digital sound-amplifying channels.

SUBSTANCE: proposed method is characterized in division of dynamic range of signal to be amplified into two regions, one being low-value region and other, high-value one, followed by separate amplification of signals resulting from this operation. Expected enhanced quality of amplified signal is attained due to amplifying weak signal by means of low-power precision analog amplifier and strong one, by heavy-power amplifier, such as that operating in class D mode. Digital amplifier implementing proposed method is built around two channels of which one incorporates analog-to-digital converter and analog amplifier and other channel, digital-code-to-pulse-train converter and pulse amplifier with demodulator.

EFFECT: reduced output signal distortions at low level of input signal being amplified.

12 cl, 5 dwg

Description

The invention relates to amplification technology and is mainly intended for use in digital sound reproducing paths operating with digital signal sources, for example, Audio-CD, DVD-Audio, etc.

The amplification of the signals, presented in the form of a pulse sequence modulated according to one of the time parameters, makes it possible to use directly to increase the amplitude and power of the signals cascades operating in a class D mode, characterized in that the transistors are either in a saturation or cutoff state. The above provides a sufficiently high efficiency of amplifiers, unattainable for Class B circuits. The most common type of modulation in Class D amplifiers is pulse width modulation (PWM), and there are also pulse frequency modulation amplifiers, less often with a combination of several types of modulation. PWM sequence demodulation is carried out quite simply by low-pass filters (low-pass filters), often the role of which is played by frequency-selective loading.

The classical method of amplifying signals by converting them to a pulse sequence is that the amplified analog signal is converted into a PWM sequence using it as a modulating one, then the pulses of the PWM sequence are amplified, after which the PWM sequence is demodulated, thereby isolating the amplified analog signal [Shkritek P. Reference manual for sound circuitry. - M .: Mir, 1991, pp. 226-227; Controller class-D audio amplifier TDA 8929T. Philips Semiconductors, 2001].

The method is used to amplify signals received from analog sources. At the same time, a significant part of modern storage media contains information presented in digital form. In these cases, it is advisable to apply a digital code to the amplifier input as a primary signal, without converting it into an analog form. This method is also known, differs little from the first and consists in the following.

The method (prototype) of amplification of signals presented in digital form, consisting in the fact that an N-bit digital code is converted into a sequence of pulse-width modulated pulses that amplify, and after amplification, the PWM sequence is demodulated, thereby converting the original digital signal into an analog [ TAS 5001 digital audio PWM processor, Texas Instruments, 2001].

A digital amplifier that implements the prototype method comprises a digital code converter (pulse-code modulated (PCM) signal) into a PWM sequence, a pulse amplifier and a low-pass filter, the input of which is connected to the output of the pulse amplifier, the input of which is connected to the output of the converter, the input of which serves as the input of a digital amplifier, the output of which is the output of the filter [TAS 5001 digital audio PWM processor. Texas Instruments, 2001; TAS 5100A PWM power output stage. Texas Instruments, 2002].

The disadvantage of both the prototype method and the devices that implement it is the increase in non-linear distortion of the output signal with a decrease in the level of the input amplified. This reason hinders the use of class D amplifiers in the tasks of high-precision sound amplification.

The technical result achieved using the present invention is to reduce the distortion of the output signal at a low level of the input, amplified signal.

The technical result is achieved by the fact that in the method of amplifying the signals presented in digital form, according to the invention, the bits of the digital code corresponding to the count of the analog signal are divided into two groups — the group of the least significant bits and the group of the highest bits, the digital signal corresponding to the group of the least significant bits is converted into analog form, amplified in analog form and get the first component of the output signal, the digital signal corresponding to the group of senior bits is converted into a sequence of pulses, modulated by one or more time parameters, the pulses are amplified, after which they are demodulated and a second component of the output signal is obtained, the weighted sum of the components is the output amplified signal.

The digital signal corresponding to the high-order group can be converted into a sequence of pulse-width modulated pulses, or into a sequence of frequency-modulated pulses, or into a sequence of frequency and pulse-width modulated pulses.

The technical result is also achieved by the fact that the hybrid amplifier according to the first embodiment, including a pulse amplification channel, comprising a digital code converter into a sequence of pulses modulated by one or more time parameters, a pulse amplifier with a demodulator, according to the invention, comprises an adder and an analog gain channel, containing a digital-to-analog converter and an analog amplifier, a pulse channel is used to amplify a signal corresponding to a group of senior bits in the amplified signal, analog channel for amplifying a signal corresponding to the group LSBs of the amplified signal, an adder is used for adding the output signals of two channels output of the adder serves to connect the load.

The technical result is also achieved in that the hybrid amplifier according to the second embodiment, comprising a pulse amplification channel, comprising a digital code converter into a sequence of pulses modulated by one or more time parameters, a pulse amplifier with a demodulator according to the invention comprises an analog gain channel containing a digital-to-analog converter and an analog amplifier, a pulse channel is designed to amplify the signal corresponding to the group of senior digits th signal channel is for the analog gain signal corresponding group of LSBs of the amplified signal, the two channel gain included in antiphase outputs channels serve for connecting to them the load.

The digital code to pulse train, which is part of the pulse channel of the hybrid amplifier, can be made in the form of a device that converts a digital signal into a sequence of pulse-width modulated pulses, or into a sequence of frequency-modulated pulses, or into a sequence of frequency and width-modulated pulses.

The invention is illustrated graphic material. Figure 1 shows a timing diagram illustrating a method of amplifying digital signals, figure 2 is a functional diagram of a first embodiment of a hybrid amplifier, figure 3 is a functional diagram of a second embodiment of a hybrid amplifier.

The timing diagram (figure 1) contains:

- signal u ₁ (t) from the region of small values of the dynamic range and corresponding to the group of lower digits, signal u ₂ (t) = 0 from the region of large values of the dynamic range and corresponding to the group of senior digits at u _in1 (t), not exceeding the region small values (u _in1 (t) is the input amplified signal), the output signal is u _S (t) (figa);

- signal u ₁ (t) from the region of small values of the dynamic range and corresponding to the group of lower digits, the signal u ₂ (t) from the region of large values of the dynamic range and corresponding to the group of senior digits at u _in2 (t)> u _in1 (t), the output signal u _S (t) (figb);

- signal u ₁ (t) from the region of small values of the dynamic range and corresponding to the group of lower digits, signal u ₂ (t) from the region of large values of the dynamic range and corresponding to the group of senior digits at u _in3 (t)> u _in2 (t), the output signal u _S (t) (figv);

Timing diagrams (Fig. 1) are obtained by functional modeling of the process of amplification of an eight-digit digital code, divided into two groups of bits according to the circuit shown in Fig. 2.

The functional diagram of the digital amplifier of FIG. 2 contains a 4-bit digital-to-analog converter (DAC) 1, a 4-bit PCM-PWM converter 2, an analog amplifier 3, a 4 pulse amplifier with a demodulator and an adder 5. The output of adder 5 is the output of the hybrid amplifier , The 8-bit input of which is the inputs of the converters 1 and 2, the outputs of which are connected to the inputs of the amplifiers 3 and 4, respectively, the outputs of which are in turn connected to the inputs of the adder 5. The input of the DAC 1 is a group of the least significant bits of the input code, the input pre Browser PCM-PWM 2 is a group of high order bits of the input code.

The functional diagram of the digital amplifier of FIG. 3 comprises a 4-bit DAC 6, a 4-bit PCM-PWM converter 7, an analog amplifier 8, a pulse amplifier 9 with a demodulator, and an amplifier load with resistance R _L. The load of the digital amplifier is connected between the outputs of the amplifiers 8 and 9, the inputs of the converters 6 and 7, the outputs of which are connected to the inputs of the amplifiers 8 and 9 pulses, respectively, serve as the 8-bit input of the digital amplifier. The input of the DAC 6 is a group of the least significant bits of the input code, the input of the converter PCM-PWM 7 is a group of the highest bits of the input code.

It is known that the number U - the countdown of the analog signal - in positional notation with base 2 is expressed as a series

U = a _N-1 2 ^N-1 + a _N-2 2 ^N-2 + ... + a ₂ 2 ² + a ₁ 2 ¹ + a ₀ 2 ⁰ ,

where N is the number of bits (positions) of the selected number system, in this case it is equal to the number of bits of the binary code U (n) = (a _N-1 , and _N-2 , ..., and ₁ , and ₀ );

a _n is the value of the nth digit (n = 0, 1, 2, ... N-1)

2 ⁿ is the weight of the n-th digit.

The presented expression of any capacity (if N is a finite number) can be transformed using the distributive property and obtain a weighted sum of several groups as a result.

As an illustration, we give the count U, described by an eight-bit binary code.

U = 2 ⁴ (a ₇ 2 ³ + a ₆ 2 ² + a ₅ 2 ¹ + a ₄ 2 ⁰ ) + a ₃ 2 ³ + a ₂ 2 ² + a ₁ 2 ¹ + a ₀ 2 ⁰ .

In this example, we have two four-bit groups: the first is enclosed in brackets and is a group of high-order bits with a total weight factor of 2 ⁴ , and the second group is a group of low-order bits, represented by the first four members on the right. It can be seen from the above record that the group of digits, indicated by brackets, has the same bit weights as the group of the lower four digits. Therefore, we can assume that the eight-digit binary number u _S (n) = (a ₇ , a ₆ , ..., a ₁ , a ₀ ) is presented in the form of the sum of two four-digit numbers u ₁ (n) = (a ₃ , a ₂ , a ₁ , a ₀ ) and u ₂ (n) = (a ₇ , a ₆ , a ₅ , a ₄ ) the last of which is involved in addition with the weight coefficient. The analog signals u ₁ (t) and u ₂ (t) shown in FIG. 1 are obtained by converting from four-digit binary codes u ₁ (t) and u ₂ (t), respectively, and taking into account weighting factors. The weighted sum of the two analog signals u ₁ (t) and u ₂ (t) gives a copy of the original signal u _S (t) (of course, with sampling and quantization errors)

u _S (t) = u ₂ (t) + u ₁ (t) = 2 ⁴ u ₀₂ (t) + u ₁ (t),

where u ₀₂ (t) is the signal corresponding to the group of senior digits without taking into account the weight coefficient.

Thus, in order to amplify the signal represented in the eight-bit binary code u _S (t), it can be divided into two low-resolution signals and separately amplified each of them.

The method is based on the idea of dividing the dynamic range of the signal into two regions - the region of small values and the region of large values, and then separate amplification of the signals obtained as a result of such separation. The expected effect - improving the quality of the amplified signal - is ensured by amplifying a weak signal with a low-power analog precision amplifier, and a strong one with an economical powerful amplifier, for example, operating in class D. Considering that the nonlinear distortions of the latter type of amplifiers are large for small values of the input signal, it is advisable to use a pulse amplifier to amplify only strong signals, that is, in the region of large values where high profitability is required and permissible linearity.

To explain the principle of separate amplification, we turn to Fig. 1, where three cases of amplification of signals differing in amplitudes u _in1 (t) <u _in2 (t) <u _in3 (t) are _shown . With a weak input signal u _in1 (t) (Fig.1a), when the range of its instantaneous values fits into the group of the least significant bits of the digital code that carries information about this signal, amplification occurs only in the analog channel, including DAC 1 and analog amplifier 3 (see figure 2). The total output signal u _S (t) = u ₁ (t) consists only of the first component, since u ₂ (t) = 0. With an increase in the input signal level and, for example, when u _u2 (t) is reached (Fig. 1b), a group of high-order bits is also activated, the signal from which is removed for amplification in a pulse channel consisting of an PCM-PWM converter 2 and an economical pulse amplifier 4. The signals u ₁ (t) and u ₂ (t) are summed in block 5, and an amplified signal u _S (t) = u ₁ (t) + u ₂ (t) is formed at the output of the amplifier, including the first and the second component. Similarly, amplification occurs at a higher signal level u _in3 (t). The weighting summation in the present example can be carried out both by using a weighting adder and by selecting the amplification factors K _U1 and K _{U2 of} amplifiers 3 and 4, respectively, so that the condition (K _U1 / K _U2 ) = 2 ^{4 is} satisfied (ratio gain factors are selected equal to the weight coefficient related to the group of senior digits).

, представляя исходный отсчет U в виде:In the general case, when dividing an N-bit binary code into two equal groups, a group of higher digits is assigned a common weight coefficient equal to

presenting the original reference U in the form:

-разрядных кодаand form for further transformations and amplification two

-bit code

and

Of course, a hybrid amplifier can be designed to work with digital codes of arbitrary bit depth, divided into groups of equal and different bit depths.

The circuit shown in Fig. 3 differs from the above only in that the addition of signals occurs directly in the load R _L due to the inclusion of amplifiers 8 and 9 in antiphase, therefore, when the load R _{L is} connected between the outputs of the amplifiers, a potential difference will be applied to it, defined by the sum of the modules u ₁ (t) and u ₂ (t). The weighting summation in this case occurs due to the choice of amplification factors K _U1 and K _{U2 of} amplifiers 8 and 9, respectively, so that the condition (K _U2 / K _U1 ) = 2 ^{4 is} fulfilled.

Claims (12)

1. A method of amplifying signals, characterized in that the bits of the digital code corresponding to the sample of the analog signal are divided into two groups — the group of the least significant bits and the group of the highest bits, the digital signal corresponding to the group of the least significant bits is converted into an analog form, amplified in an analog form and receive the first component of the output signal, the digital signal corresponding to the group of senior digits is converted into a sequence of pulses modulated by one or more time parameters, the amplification pulses They are then demodulated and the second component of the output signal is obtained, the weighted sum of the components is the output amplified signal. 2. The method according to claim 1, characterized in that the digital signal corresponding to the high order group is converted into a sequence of pulse-width modulated pulses. 3. The method according to claim 1, characterized in that the digital signal corresponding to the high-order group is converted into a sequence of frequency-modulated pulses. 4. The method according to claim 1, characterized in that the digital signal corresponding to the high-order group is converted into a sequence of frequency and width-modulated pulses. 5. A hybrid amplifier, including a pulse amplification channel, comprising a digital code converter into a sequence of pulses modulated by one or more time parameters, a pulse amplifier with a demodulator, characterized in that an adder and an analog gain channel containing a digital-to-analog converter are inserted into it and an analog amplifier, a pulse channel is designed to amplify the signal corresponding to the group of high-order bits of the amplified signal, the analog channel is intended for amplification To add a signal corresponding to the group of the least significant bits of the amplified signal, the adder serves to add the output signals of two channels, the output of the adder serves to connect the load. 6. The hybrid amplifier according to claim 5, characterized in that the digital code to pulse train included in the pulse channel is made in the form of a device that converts a digital signal into a sequence of pulse-width modulated pulses. 7. The hybrid amplifier according to claim 5, characterized in that the digital code to pulse train included in the pulse channel is made in the form of a device that converts a digital signal into a sequence of frequency-modulated pulses. 8. The hybrid amplifier according to claim 5, characterized in that the digital code to pulse train included in the pulse channel is made in the form of a device that converts a digital signal into a sequence of frequency and width-modulated pulses. 9. A hybrid amplifier, including a pulse amplification channel, comprising a digital code converter into a sequence of pulses modulated by one or more time parameters, a pulse amplifier with a demodulator, characterized in that an analog amplification channel is introduced into it, comprising a digital-to-analog converter and an analog amplifier , the pulse channel is designed to amplify the signal corresponding to the high order group of the amplified signal, the analog channel is intended to amplify the signal a corresponding group of LSBs of the amplified signal, the two channel gain included in antiphase, output channels are used for connecting a load thereto. 10. The hybrid amplifier according to claim 9, characterized in that the digital code to pulse train included in the pulse channel is made in the form of a device that converts a digital signal into a sequence of pulse-width modulated pulses. 11. The hybrid amplifier according to claim 9, characterized in that the digital code to pulse train included in the pulse channel is made in the form of a device that converts a digital signal into a sequence of frequency-modulated pulses. 12. The hybrid amplifier according to claim 9, characterized in that the digital code to pulse train included in the pulse channel is made in the form of a device that converts a digital signal into a sequence of frequency and width-modulated pulses.

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