JPH0779256B2 - Quantizer - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quantizer for converting a digital signal having a long word length into a digital signal having a short word length sampled at high speed.

2. Description of the Related Art In recent years, with the improvement of digital signal processing technology, signals that have been conventionally analog processed have been digitally processed.
Along with this, higher performance and lower cost of digital-analog converters have become more important. Noise-shaping quantizers are often used for these purposes. As a quantizer using noise shaping, for example, Japanese Patent Laid-Open No. 63-209334 discloses a quantizer of a multi-stage noise shaping type. By using this quantizer, stable high-order noise shaping can be performed without causing oscillation or the like.

However, on the other hand, there is also a problem that the gradation of the quantizer output increases. Therefore, a method has been proposed in which this quantizer is improved so as to suppress an increase in gradation of the quantizer output.

The block diagram is shown in Fig. 5 and explained (for example, Journal of solid state circuit, Aug.1989, Vo.
l.24, No.4).

The delay circuit 127 and the adder 126 form an integrator 102. Local quantizer 103, adder 128, delay circuit 4, subtractor 101,
Main loop 10 which is a single integral type noise shaping quantizer having a first-order shaping order by integrator 102
0 is configured. Further, the adder 120 and the delay circuit 121 configure the integrator 108, and the adder 122 and the delay circuit 123 configure the integrator 1.
10 are configured. The subtractors 107 and 109, the local quantizer 6, the integrators 108 and 110, and the delay device 112 constitute a sub-loop 106 which is a double integral type noise shaping quantizer having a quadratic shaping order. Subloop 106
Is given to the input / output difference of the local quantizer 103 by the subtractor 2. The output of the integrator 108 is the multiplier 130.
After being multiplied by the coefficient a, it is added to the input of the local quantizer 103 via the adder 128.

Here, the input X is a 16-bit digital signal, and the local quantizers 103 and 6 perform the quantization as shown in Tables 1 and 2. The output is standardized at 16384.

Here, the quantization error generated by the local quantizer 103 is Vq1, and the quantization error generated by the local quantizer 6 is Vq1.
Let q2 be the relationship between the input X and output W of the main loop 100,
The relationship between the input X'and the output W'of the sub-loop 106 is expressed by the equations (1) and (2).

W = X + (1-z -1) · Vq1 ... (1) W '= X' + (1-z -1) 2 · Vq2 ... (2) where the adder output of the 2 local quantizer 103 Therefore, the output W'of the sub-loop 106 is differentiated by the differentiator 10 composed of the subtracter 13 and the delayer 14 by the following X '=-Vq1 (3), and then is added by the adder 12 to the main When added to the output W of the loop 100, the term of Vq1 shown in the equation (1) is canceled out, and the relation between the input and output X, Y as a whole is as shown in the equation (4).

Y = X + (1−z ⁻¹ ) ³ · Vq2 (4) Here, the reason why this circuit operates stably despite the gradation of the sub-loop is ± 05 is as follows. That is, the value of the integrator 108 is fed back by the multiplier 130 to the local quantizer 103 via the adder 128. Therefore, when the value of the integrator 108 is large, the local quantizer 103
Since the input of is also large, the value of the subtractor 2 becomes a large negative value. This value is given to the integrator 108 via the subtractor 107, but since the other input of the subtractor 107 is 0.5 at the most, a large negative value is input to the integrator 108 and gradually increases. The output of the integrator 108 becomes small.

In this way, by feeding back the main loop 100 in the direction in which the value of the integrator 108 becomes smaller, the input of the local quantizer 6 can be suppressed to a smaller value, and the output level of the local quantizer 6 can be reduced. The tone can be lowered.

Here, the possible values of W, that is, the gradation is −2, −1, ...,
There are 5 ways of +2 (5 values), and the possible value of W'is -0.
Since it is a binary value of 5, +0.5, the possible values of Y are -3, -2,
…, 7 values of +3. That is, the input signal is 7-valued (3
It shows that it is compressed to a little bit). Also,
Equation (4) shows that the quantization error in the low frequency band is driven to the high frequency band. Therefore, by configuring as shown in FIG. 5, the output is performed without damaging the dynamic range of the input digital signal. The bit number of the digital signal can be compressed, and a dynamic range of about 118 dB can be obtained by operating this circuit with 64 times oversampling.

However, in the above configuration, after the value of the integrator 108 in the subloop 106 is determined, the output of the integrator 108 → the multiplier
130 → adder 128 → local quantizer 103 → subtractor 2 → subtractor 1
The calculation must be performed again through the path of 07 → integrator 108 → subtractor 109 → integrator 110 → local quantizer 6, which requires a very long calculation time. Moreover, the feedback is applied from the output of the integrator 108, which is the first-stage integrator, and the subsequent integrator 110 has no feedback. Therefore, it is almost impossible to prevent oscillation or overflow in the integrator 110. Therefore, for example, there is a problem that it is difficult to use a sub-loop having a shaping order of 3 or higher.

In view of the above problems, the present invention requires less calculation time,
It is an object to provide a quantizer that can obtain the same effect.

Means for Solving the Problems To achieve the above object, a quantizer according to the present invention comprises a first local quantizer for quantizing an input signal, and a first local quantizer for noise shaping of a given input. Noise shaping type quantizer, a second local quantizer for quantizing an input signal, a detecting means for detecting a quantization error generated by the second local quantizer, and a detecting means for detecting the quantizing error. A feedback circuit for multiplying the output by a predetermined transfer function and feeding it back,
The quantization error generated by the first noise shaping quantizer and the output of the feedback circuit are added and input to the second local quantizer, and the output level of the output of the feedback circuit and the first local quantizer are added. Based on the quantization error generated by the noise shaping quantizer, a control means for adding / subtracting a predetermined value to / from the output value of the first local quantizer is provided, and the output of the second local quantizer is set. The first noise shaping quantizer is differentiated according to the order, the differentiated output and the output of the control means are added, and the addition result is taken out as an output.

Alternatively, it has a first local quantizer for quantizing an input signal, a first noise-shaping quantizer for noise-shaping a given input, and a second noise-shaping quantizer for quantizing an input signal. A local quantizer, detection means for detecting a quantization error generated by the second local quantizer, and a feedback circuit for multiplying the output of the detection means by a predetermined transfer function to feed back the output. The quantization error generated by the first noise shaping quantizer and the output of the feedback circuit are added to be input to the second local quantizer, and the output level of the output of the feedback circuit is set. Based on the order of the first noise shaping quantizer, the second local quantizer output according to the order of the first noise shaping type quantizer, and a control means for adding and subtracting a predetermined value to and from the output value of the first local quantizer. The differential output and the output of the control means Added by differentiating the bets, in which they were taken out of the addition result as an output.

Function As described above, the output of the local quantizer in the main loop is +1, +2, ... Or -1, -2, depending on the output of the feedback circuit and the value of the quantization error generated by the main loop.
..., so that the quantization error generated by the main loop is always opposite to the output of the feedback circuit, and the value of the quantization error generated by the main loop depends on the value of the output of the feedback circuit. Change. Therefore, the absolute value of the input level of the local quantizer in the sub-loop to which the addition result of this value and the output of the feedback circuit is input is always smaller than a certain value, and the gradation of the local quantizer in the sub-loop is reduced. be able to. Further, since the output of the feedback circuit is fixed in advance, the time required for the calculation can be shortened.

Examples Hereinafter, the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of a quantizer according to the present invention. Referring to this figure, 1 is a local quantizer, which quantizes an input signal. The relationship between input and output is as shown in Table 3. The output is standardized by 1264.

Reference numeral 5 is a control circuit for adding the output of the amplitude detector 11 and the output of the local quantizer 1, which will be described later, and has a configuration as shown in FIG. That is, the adder 20 outputs the output C of the amplitude detector 11 and the output Q1 of the local quantizer 1.
And are added, and the limiter 21 prevents the result from exceeding -3 to +3. Reference numeral 6 is a local quantizer, and the relationship between the input and the output is as shown in Table 3. Reference numeral 9 is a feedback circuit, and its transfer function H (z) is as shown in the expression (5), and specifically has a configuration as shown in FIG.

H (z) = − 2z ⁻¹ + z ⁻² (5) That is, the input is given to the delay circuit 41, the difference between the output doubled by the multiplier 44 and the output of the delay circuit 42 is subtracted.
43 required. 11 is an amplitude detector, which is a subtractor 2
Is the output of the main loop (-Vq
1) and the output β of the feedback circuit 9 are input, and a 3-bit signal C (C ₂ , C ₁ , C ₀ ) is output here according to their levels. It is as shown in.

Next, the operation of the circuit shown in FIG. 1 will be described. The adder 3, the local quantizer 1, the control circuit 5, the subtractor 2, and the delay unit 4 constitute a main loop of single integration type noise shaping. If the quantization error generated by both the local quantizer 1 and the control circuit 5 is Vq1, the output of the subtractor 2 is -V.
It becomes q1. Since this value is fed back to the input via the delay unit 4, the output W of the control circuit 5 is as in the equation (6) as in the case of the conventional example.

W = X + (1−z ⁻¹ ) · Vq1 (6) On the other hand, the local quantizer 6, the adder 7, the subtractor 8 and the feedback circuit 9 constitute a double integral type noise shaping subloop. Here, considering the input to the local quantizer 6, this value is obtained by subtracting the quantization error Vq1 generated by the main loop from the feedback amount β by the feedback circuit 9. With the amplitude detector 11, the feedback amount β = 20000,
When the input of the sub-loop (-Vq1) = 12000, the output of the local quantizer 1 is +2 according to Table 5, and the input P'of the local quantizer 6 is P '= 12000-11264 × 2 + 20000 = 9472 ( 7), which is always smaller than the feedback amount β and can be suppressed to 11264 or less which is the input limit of the local quantizer 6.
Therefore, as in the prior also in this circuit example, as Vq2 the quantization error local quantizer 6 is generated, W '= - Vq1 + ( 1-z -1) 2 · Vq2 ... (8), adding the output Y of the vessel 12 will be Y = W + (1-z -1) · W '= X + (1-z -1) 3 · Vq2 ... (9) , and the third-order noise shaping obtained. In this case, the output of the local quantizer 1 is 7 from -3 to +3.
Since this is a value, and the output of the local quantizer 6 is a binary value of ± 0.5, the final output Y is a nine value from -4 to +4, and the same shaping effect as in the conventional example can be obtained.

Here, considering the signal transmission path, as can be seen from FIG. 3, the output of the feedback circuit 9 is fixed regardless of the output of the amplitude detector 11, and only the sign of the output of the subtractor 2 matters. Become. Here, even if the sign of the output of the feedback circuit 9 and the sign of the output of the subtractor 2 are different, the signal transmission path is as follows: amplitude detector 11 → control circuit 5 → subtractor 2 → adder 7 → subtract It is significantly shorter than that of the device 8 or the local quantizer 6. As for the feedback to the main loop, the feedback is applied so that the value to be input to the local quantizer 6 becomes small. Therefore, the feedback is applied to the entire sub loop, and the degree of freedom in designing the feedback circuit 9 is increased. Therefore, even if the characteristic of the feedback circuit 9 is third or higher, the circuit can operate stably. That is, for example, the local quantizer 6 shown in Table 4 may be used, and the transfer function of the feedback circuit 9 may be of a higher order as shown in equation (10).

If this transfer function is used, a fourth-order noise shaping effect can be obtained in the low frequency range, and a dynamic range of about 118 dB can be obtained by operating this circuit with 32 times oversampling.

FIG. 4 shows another embodiment of the quantizer according to the present invention. In this figure, components having the same functions as those in FIGS. 1 to 3 are designated by the same reference numerals, and detailed description thereof will be omitted. The difference between this embodiment and the embodiment shown in FIG. 1 is that
The amplitude detector 15 is compared with the amplitude detector 11 in FIG. 1 in which the outputs of both the subtractor 2 and the feedback circuit 9 are input. Is input. The input / output relationship of this amplitude detector 15 is the sixth
It is as shown in the table.

Even with this configuration, the operation is almost the same as in FIG.
Since the value output from the subtractor 2 tends to cancel the output from the feedback circuit 9, the sub-loop operates stably, and a larger shaping effect can be obtained with fewer gray scales.

In the above embodiments, the local quantizer 1 which outputs 5 values from -3 to +3 is used, but of course, the present invention is not limited to this, and 6 values or more or 5 values or less are used. It can be one. Further, the case where the transfer function of the feedback circuit 9 shown in the equation (5) or (10) is used and the local quantizer 6 having a binary or ternary output is shown. Needless to say, it is not limited to this. Also, the amplitude detector 1
The output values of 1,15 are not limited to those shown in Table 5 or 6, and +3 and -3 are also output.
Alternatively, it may be one that outputs only ± 1 and 0. Also, the main loop does not have to be a single-integration type noise shaping circuit, in short, the quantization error generated in this loop is input to the sub-loop, and the feedback amount of the quantization error in the sub-loop and the sub-loop are input. It suffices to control addition, subtraction, etc. to the local quantizer output of the main loop according to the value from the main loop.

As described above, the present invention has the first local quantizer for quantizing the input signal, and the first noise shaping quantizer for performing noise shaping of the given input, A second local quantizer for quantizing the input signal, a detecting means for detecting a quantization error generated by the second local quantizer, and an output of the detecting means multiplied by a predetermined transfer function. A feedback circuit for feeding back, and adding the quantization error generated by the first noise shaping quantizer and the output of the feedback circuit and inputting to the second local quantizer. Control means for adding or subtracting a predetermined value to or from the output value of the first local quantizer based on the output level of the output of the feedback circuit and the quantization error generated by the first noise shaping quantizer. And a second local quantizer output By differentiating the force according to the order of the first noise shaping quantizer, adding the differentiated output and the output of the control means, and taking out the addition result as an output, or Having a first local quantizer for quantizing the
Noise shaping type quantizer, a second local quantizer for quantizing an input signal, a detecting means for detecting a quantization error generated by the second local quantizer, and a detecting means for detecting the quantizing error. A feedback circuit that multiplies the output by a predetermined transfer function and feeds it back, and adds the quantization error generated by the first noise shaping quantizer and the output of the feedback circuit to the second Control means for inputting to the local quantizer and adding or subtracting a predetermined value to or from the output value of the first local quantizer based on the output level of the output of the feedback circuit. The output of the digitizer is differentiated according to the order of the first noise shaping quantizer, the differentiated output and the output of the control means are added, and the addition result is taken out as the output. Local quantizer floor Fewer, it can reduce the tone of the whole quantizer. Further, even when a sub-loop feedback circuit having a quadratic degree or more is used, it is possible to suppress the oscillation of the feedback circuit without increasing the gradation, and further, it is possible to reduce the time required for the calculation. Is to have.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a quantizer according to the present invention, FIG. 2 is a block diagram showing a concrete embodiment of the amplitude detector 11, and FIG. 3 shows details of a feedback circuit in the same embodiment. FIG. 4 is a block diagram showing another embodiment of the quantizer according to the present invention, and FIG. 5 is a block diagram showing a conventional quantizer. 1,6 ...... Local quantizer, 4 ...... Delay circuit, 5 ...... Control circuit, 9 ...... Feedback circuit, 10 ...... Differentiator, 11, 15 ...... Amplitude detector.

Continuation of the front page (56) Reference JP-A-54-99545 (JP, A) JP-A-61-84914 (JP, A) JP-A-63-161713 (JP, A) JP-A-3-289709 (JP , A) JP 4-56407 (JP, A) JP 3-289808 (JP, A) JP 3-289809 (JP, A) JP 4-30618 (JP, A) JP 4-30619 (JP, A) JP-A-4-30620 (JP, A) JP-B 6-83150 (JP, B2)

Claims (3)

[Claims] 1. A first noise-shaping quantizer for noise-shaping a given input, and a first local quantizer for quantizing an input signal, and quantizing an input signal. A second local quantizer, a detecting means for detecting a quantization error generated by the second local quantizer, and a feedback circuit for feeding back an output of the detecting means by multiplying a predetermined transfer function by feedback. Then, the quantization error generated by the first noise shaping quantizer and the output of the feedback circuit are added to be input to the second local quantizer, and the output of the feedback circuit And a control means for adding or subtracting a predetermined value to or from the output value of the first local quantizer based on the output level and the quantization error generated by the first noise shaping quantizer. The output of the local quantizer is the first noise Differentiated according to the degree of Epingu type quantizer adds the output of the control means and its differential output, the quantizer which is to extract the addition result as an output. 2. A first noise-shaping quantizer for noise-shaping a given input, and a first local quantizer for quantizing an input signal, and for quantizing an input signal. A second local quantizer, a detecting means for detecting a quantization error generated by the second local quantizer, and a feedback circuit for feeding back an output of the detecting means by multiplying a predetermined transfer function by feedback. Then, the quantization error generated by the first noise shaping quantizer and the output of the feedback circuit are added to be input to the second local quantizer, and the output of the feedback circuit Control means for adding / subtracting a predetermined value to / from the output value of the first local quantizer based on the output level is provided, and the output of the second local quantizer is set to the order of the first noise shaping quantizer. According to the differential output and the control means Added by differentiating the output, the quantizer which is to extract the addition result as an output. 3. The quantizer according to claim 1 or 2, wherein a value after the output value of the first local quantizer is controlled by the control means is within a predetermined value.