A spectrum shaping circuit based on vector filtering DEM

Abstract

A spectrum shaping circuit based on vector filter DEM, comprising a Sigma-Delta modulator, a DEM circuit and a multi-bit DAC; the DEM circuit includes a vector filter and a vector sorter, the vector filter includes 2 type-I integrators, 2 type-II integrators, 2 resonant circuits with gains of Kg1 and Kg2 respectively, 4 feedforward paths with gains of K1, K2, K3 and 1 respectively, 3 digital adders and 1 delay element z-1; the Sigma-Delta modulator receives an input signal u(t), the output signal v[n] of the Sigma-Delta modulator is sent to the vector sorter of the DEM circuit, and after being processed by the vector filter of the DEM circuit, the output signal of the vector sorter is sent to the multi-bit DAC, and the multi-bit DAC outputs a shaped signal r(t). The present invention can provide stable mismatch shaping and improve the SNR.

Description

Technical Field

[0001] The present invention belongs to the field of analog integrated circuit design, and particularly relates to a spectrum shaping circuit based on vector filter DEM. Background Art

[0002] Multi-bit Sigma-Delta modulators have better stability and signal-to-noise ratio than single-bit Sigma-Delta modulators. The disadvantage of multi-bit DACs is that they cannot guarantee linearity due to unit element mismatch. To solve this problem, researchers have developed DEM circuits based on minimum-subtraction stability and techniques for mismatch shaping based on standard-integral all-feedback DEM circuits. Although these techniques can achieve mismatch shaping at high oversampling rates, their noise and harmonic suppression capabilities under high-order conditions are very limited. For example, based on the standard-integral all-feedback DEM circuit, not only can it not achieve notch filtering to improve SNR under the condition of adding a resonant circuit, but also the stability of mismatch shaping will be limited. Although the DEM circuit based on minimum-subtraction stability can achieve notch filtering under the condition of adding a resonant circuit, the output of the vector filter is large, reducing the hardware efficiency. Summary of the Invention

[0003] The object of the present invention is to provide a spectrum shaping circuit based on vector filter DEM for the problems in the above-mentioned prior art, overcome the problem that the noise and harmonic suppression capabilities of existing DEM circuits are limited under high-order conditions, provide stable mismatch shaping, improve SNR, and be able to achieve vector filtering with high hardware efficiency and bounded integrator vector output.

[0004] To achieve the above object, the present invention has the following technical solutions:

[0005] A spectrum shaping circuit based on vector filter DEM includes a Sigma-Delta modulator, a DEM circuit, and a multi-bit DAC; the DEM circuit includes a vector filter and a vector sorter, and the vector filter includes 2 type-I integrators, 2 type-II integrators, 2 resonant circuits with gains of K g1 and K g2 , 4 feedforward paths with gains of K1, K2, K3, and 1, 3 digital adders, and 1 delay element z -1 ;

[0006] One digital adder, one type-I integrator, and one type-II integrator are connected in series to form one vector filter branch. In this way, the first vector filter branch and the second vector filter branch are formed and connected in series; a resonant circuit with a gain of K g1The resonant circuit, a gain of K is connected between the output terminal of the type-II integrator of the second vector filter branch and its digital adder g2 The resonant circuit; the output signals of the type-I integrators and type-II integrators of the two vector filter branches are connected to one digital adder, the output signal of this digital adder is sent to the vector sorter, and the vector sorter passes through the delay element z -1 is connected to the digital adder of the first vector filter branch;

[0007] The Sigma-Delta modulator receives the input signal u(t), the output signal v[n] of the Sigma-Delta modulator is sent to the vector sorter of the DEM circuit, and after being processed by the vector filter of the DEM circuit, the vector sorter outputs the signal is sent to the multi-bit DAC, and the multi-bit DAC outputs the shaped signal r(t).

[0008] As a preferred embodiment of the present invention, the type-I integrator includes two digital adders, a delay element z -1 , a scalar negative feedback loop with a gain of K * and a vector-to-scalar adder ∑ VTS}{}, the two digital adders are connected in series, and are respectively the first-stage digital adder and the second-stage digital adder according to the signal flow direction, the signal is input by the first-stage digital adder and output by the second-stage digital adder, and the vector-to-scalar adder ∑ VTS}{} is led out between the two digital adders and is connected to the second-stage digital adder through the scalar negative feedback loop with a gain of K * , the output terminal of the second-stage digital adder is feedback-connected to the first-stage digital adder through the delay element z -1 .

[0009] As a preferred embodiment of the present invention, the type-II integrator includes two digital adders, a delay element z -1 , a scalar negative feedback loop with a gain of K * and a vector-to-scalar adder ∑ VTS}{}, the two digital adders are connected in series, and are respectively the first-stage digital adder and the second-stage digital adder according to the signal flow direction, the signal is input by the first-stage digital adder and output by the second-stage digital adder, and the delay element z -1 is connected between the two digital adders, and the vector-to-scalar adder Σ VTS}{} is led out between the delay element z -1 and the second-stage digital adder and passes through the scalar negative feedback loop with a gain of K *The scalar negative feedback loop is connected to the second-stage digital adder, and the output end of the second-stage digital adder is feedback-connected to the first-stage digital adder.

[0010] As a preferred embodiment of the present invention, the gain is K * K in the scalar negative feedback loop * = 1 / (2^N).

[0011] As a preferred embodiment of the present invention, the vector sequencer in the DEM circuit feeds back to the vector filter in a positive feedback manner.

[0012] As a preferred embodiment of the present invention, the gain is K g1 The resonant circuit of feeds back from the output end of the type-II integrator of the first vector filter branch to its digital adder in a negative feedback manner; the gain is K g2 The resonant circuit of feeds back from the output end of the type-II integrator of the second vector filter branch to its digital adder in a negative feedback manner.

[0013] As a preferred embodiment of the present invention, if the type-I integrator and type-II integrator connected in series in the first vector filter branch and the second vector filter branch are numbered in sequence, then the output of the (i - 1)-th stage integrator serves as the input of the i-th stage integrator; the output signal of the vector sequencer and the output signal of the i-th stage integrator are both N-dimensional vectors, where i ≥ 1 and is an integer.

[0014] As a preferred embodiment of the present invention, the order of the Sigma-Delta modulator is arbitrary.

[0015] As a preferred embodiment of the present invention, the vector sequencer satisfies the following expression at any time t = nT, where n is any integer and T is the DAC sampling period:

[0016]

[0017] In the formula, sv i [n] represents the enable signal of the i-th DAC unit, v[n] is the output of the sigma-delta modulator, and N is the number of unit elements of the DAC.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects:

[0019] Compared with the DEM circuit stabilized by minimum - value subtraction, the mean value of the output vector of each stage of the integrator in the vector filter of the DEM circuit of the present invention remains constant, thereby improving the stability of the vector filter, greatly reducing the hardware bit - width of the DEM, and improving the hardware efficiency. Compared with the DEM circuit stabilized by minimum - value subtraction and the DEM circuit based on standard integral full - feedback, the spectrum shaping circuit of the present invention can exponentially reduce the number of feedback paths, thereby reducing the design complexity. Compared with the DEM circuit based on standard integral full - feedback, the spectrum shaping circuit of the present invention can stably operate in the mode with a resonant circuit, achieving an improvement in SNR and the elimination of harmonic distortion; compared with the DEM circuit stabilized by minimum - value subtraction and the DEM circuit based on standard integral full - feedback without a resonant circuit, the spectrum shaping circuit of the present invention can obtain a higher SNR. Brief Description of the Drawings

[0020] Figure 1 FIG. 1 is a schematic structural diagram of a spectrum shaping circuit based on vector - filter DEM proposed by the present invention;

[0021] FIG. 2(a) is a schematic structural diagram of the type - I integrator proposed by the present invention;

[0022] FIG. 2(b) is a schematic structural diagram of the type - II integrator proposed by the present invention;

[0023] Figure 3 FIG. 3 is a comparison diagram of the FFT output results of the DEM circuit based on standard integral full - feedback and the circuit of the present invention under the condition of adding a resonant circuit;

[0024] Figure 4 FIG. 4 is a comparison diagram of the FFT output results of the DEM circuit based on standard integral full - feedback, the DEM circuit stabilized by minimum - value subtraction, and the circuit of the present invention;

[0025] Figure 5 FIG. 5 is a comparison diagram of the output results of the vector filters of the DEM circuit stabilized by minimum - value subtraction and the spectrum shaping circuit of the present invention under the action of the same vector sorter: (a) Output result diagram of the vector filter of the DEM circuit stabilized by minimum - value subtraction; (b) Output result diagram of the vector filter of the spectrum shaping circuit of the present invention. Detailed Description of the Invention

[0026] The present invention will be further described in detail below with reference to the accompanying drawings.

[0027] The present invention provides a spectrum shaping circuit based on vector filtering DEM. Compared with the standard integral all-feedback DEM circuit, under the condition of adding a resonant circuit, the circuit of the present invention can not only work stably, but also improve the SNR and eliminate harmonic distortion. In addition, the present invention also develops a hardware-efficient vector filtering design technology. Compared with the DEM circuit based on minimum subtraction stability, it can keep the average value of the vector output of the vector filter constant and bounded, which not only improves the stability of the DEM, but also reduces the bit-width requirement of the vector filter and improves the hardware efficiency of the DEM.

[0028] See Figure 1 , the spectrum shaping circuit based on vector filtering DEM in the embodiment of the present invention includes a Sigma-Delta modulator, a DEM circuit and a multi-bit DAC. The DEM circuit includes a vector filter and a vector sorter. The vector filter includes 2 type-I integrators, 2 type-II integrators, 2 resonant circuits with gains of K g1 and K g2 , 4 feed-forward paths with gains of K1, K2, K3 and 1, 3 digital adders and 1 delay element z -1 .

[0029] 1 digital adder, 1 type-I integrator and 1 type-II integrator are connected in series to form 1 branch of the vector filter. The first vector filter branch and the second vector filter branch are formed in this way and connected in series; a resonant circuit with a gain of K g1 is connected between the output end of the type-II integrator and its digital adder of the first vector filter branch, and a resonant circuit with a gain of K g2 is connected between the output end of the type-II integrator and its digital adder of the second vector filter branch; the output signals of the type-I integrators and type-II integrators of the 2 vector filter branches are connected to 1 digital adder, and the output signal of this digital adder is sent to the vector sorter. The vector sorter is connected to the digital adder of the first vector filter branch through the delay element z -1 .

[0030] In an optional embodiment, the vector sorter in the DEM circuit feeds back to the vector filter in a positive feedback manner. The resonant circuit with a gain of K g1 feeds back from the output end of the type-II integrator of the first vector filter branch to its digital adder in a negative feedback manner; the resonant circuit with a gain of K g2 feeds back from the output end of the type-II integrator of the second vector filter branch to its digital adder in a negative feedback manner. The type-I integrators and type-II integrators connected in series of the first vector filter branch and the second vector filter branch are numbered in sequence, and the output of the (i - 1)-th stage integrator As the input of the i-th stage integrator; the output signal of the vector sorter and the output signal of the i-th stage integrator are both N-dimensional vectors, where i≥1 and is an integer. The order of the Sigma-Delta modulator is arbitrary. The vector sorter satisfies the following expressions at any time t = nT, where n is any integer and T is the DAC sampling period:

[0031]

[0032] In the formula, sv i [n] represents the enable signal of the i-th DAC unit, v[n] is the output of the sigma-delta modulator, and N is the number of unit elements of the DAC.

[0033] The Sigma-Delta modulator receives the input signal u(t), and the output signal v[n] of the Sigma-Delta modulator is sent to the vector sorter of the DEM circuit. After being processed by the vector filter of the DEM circuit, the vector sorter outputs the signal is sent to the multi-bit DAC, and the multi-bit DAC outputs the shaped signal r(t).

[0034] Referring to Fig. 2(a), the type-I integrator of the present invention includes two digital adders, a delay element z -1 , a scalar negative feedback loop with a gain of K * and a vector-to-scalar adder Σ VTS {}. The two digital adders are connected in series, and are respectively the first-stage digital adder and the second-stage digital adder according to the signal flow direction. The signal is input from the first-stage digital adder and output from the second-stage digital adder. The vector-to-scalar adder ∑ VTS {} is led out between the two digital adders and is connected to the second-stage digital adder through the scalar negative feedback loop with a gain of K * . The output end of the second-stage digital adder is feedback-connected to the first-stage digital adder through the delay element z -1 . The working principle of the type-I integrator of the present invention is as follows:

[0035]

[0036] Referring to Fig. 2(b), the type-II integrator of the present invention includes two digital adders, a delay element z -1 , a scalar negative feedback loop with a gain of K * and a vector-to-scalar adder ∑ VTSTwo digital adders are connected in series. They are respectively the first-stage digital adder and the second-stage digital adder according to the signal flow direction. The signal is input from the first-stage digital adder and output from the second-stage digital adder, and the delay element z -1 is connected between the two digital adders. The vector-to-scalar adder ∑ VTS is led out between the delay element z -1 and the second-stage digital adder and is connected to the second-stage digital adder through a scalar negative feedback loop with a gain of K * . The output end of the second-stage digital adder is feedback-connected to the first-stage digital adder.

[0037] The working principle of the integrator of type II of the present invention is as follows:

[0038] Among them

[0039] In the DEM circuit of the spectrum shaping circuit of the present invention, a resonant circuit is adopted. Therefore, notches are generated in the amplitude-frequency response of the vector filter, thereby reducing the in-band noise and harmonic distortion; by designing a new type of integrator of type I and integrator of type II, it is possible to make the output mean value of each stage of the integrator in the vector filter constant, and reduce the output vector infinity norm, and improve the stability of the vector filter.

[0040] In an optional embodiment, K * in the scalar negative feedback loop with a gain of K * = 1 / (2^N).

[0041] The vector filter of the embodiment of the present invention can make the output vector mean value of the vector filter bounded, and can greatly improve the loop stability by reducing the infinity norm of the vector entering the vector sorter; and can reduce the hardware bit width to improve the hardware efficiency of the DEM circuit; the proposed circuit design is as follows:

[0042] According to the working modes of the two integrators in FIGS. 2(a) and 2(b), it can be obtained that when K * = 1 / (2^N), the mean values of the output vectors of the integrator of type I and the integrator of type II are both constant values. Therefore, regardless of the number and value of the input vectors of the integrator, it can be ensured that the mean value of the output vector of each stage of integration in the vector filter is constant, thereby reducing the infinity norm of the output vector of the overall vector filter and improving the stability of the loop.

[0043] The spectrum shaping circuit of the present invention can operate stably in the mode with a resonant circuit compared to the standard integral full-feedback DEM circuit. Therefore, compared to the standard integral full-feedback DEM circuit, the present invention can introduce a notch in the output spectrum of and then suppress the noise at high frequencies within the bandwidth, thereby improving the SNR.

[0044] Figure 3 Figure shows the comparison of the FFT output results of the standard integral full-feedback DEM circuit and the circuit of the present invention under the condition of adding a resonant circuit in the present invention. It can be seen from Figure 3 that when two resonant circuits are introduced, due to instability, the standard integral full-feedback DEM circuit has a very high noise floor and harmonic distortion. Compared to the standard integral full-feedback DEM circuit, the spectrum shaping circuit of the present invention can operate stably and has obvious notches. Therefore, the spectrum shaping circuit of the present invention achieves a very low noise floor, eliminates harmonic distortion, and greatly improves the SNR.

[0045] The spectrum shaping circuit of the present invention can greatly improve the SNR compared to the standard integral full-feedback DEM circuit and the DEM circuit stabilized by minimum subtraction. As Figure 4 shown, compared to the standard integral full-feedback DEM circuit and the DEM circuit stabilized by minimum subtraction, the circuit of the present invention has a lower noise floor at low frequencies within the bandwidth, thereby greatly suppressing the noise introduced by DAC element mismatch and improving the SNR.

[0046] Figure 5 Figure shows the comparison of the output results of the vector filters of the DEM circuit stabilized by minimum subtraction and the spectrum shaping circuit of the present invention under the action of the same vector sequencer. It can be seen from Figure 5 Figures (a) and (b) that the output of the vector filter of the DEM circuit stabilized by minimum subtraction is larger, while the output of the vector filter of the spectrum shaping circuit of the present invention is smaller, thereby reducing the infinity norm of the vectors entering the vector sequencer, greatly improving the loop stability. And because the hardware bit width is reduced, the hardware efficiency of the DEM circuit is also improved. For the M (M is any integer)-order vector filtering, the spectrum shaping circuit of the present invention based on vector filtering DEM has an exponentially reduced number of feedback paths in the vector filter compared to the standard integral full-feedback DEM circuit and the DEM circuit stabilized by minimum subtraction. As

[0047] shown in Figure 1As shown, only 2^N feedback paths are required in the present invention; however, 4*(2^N) feedback paths are required for the standard integral full-feedback DEM circuit and the DEM circuit based on minimum-subtraction stabilization. Therefore, the present invention can greatly reduce the number of feedback paths and lower the design complexity.

[0048] The spectrum shaping circuit based on vector filter DEM proposed by the present invention has three important improvements compared with the DEM circuit based on minimum-subtraction stabilization and the standard integral full-feedback DEM circuit: 1) Compared with the DEM circuit based on minimum-subtraction stabilization, the output vector mean value of each integrator in the vector filter of the present invention remains constant, thus improving the stability of the vector filter, greatly reducing the hardware bit width of the DEM, and improving the hardware efficiency; 2) Compared with the DEM circuit based on minimum-subtraction stabilization and the standard integral full-feedback DEM circuit, the spectrum shaping circuit of the present invention can exponentially reduce the number of feedback paths, thus reducing the design complexity. 3) Compared with the standard integral full-feedback DEM circuit, the spectrum shaping circuit of the present invention can stably operate in the mode with a resonant circuit added, achieving an improvement in SNR and elimination of harmonic distortion; 4) Compared with the DEM circuit based on minimum-subtraction stabilization and the standard integral full-feedback DEM circuit without a resonant circuit, the spectrum shaping circuit of the present invention can obtain a higher SNR.

[0049] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A spectrum shaping circuit based on a vector filtering DEM, characterized in that, including a Sigma-Delta modulator, a DEM circuit, and a multi-bit DAC; the DEM circuit includes a vector filter and a vector sorter, and the vector filter includes two type-I integrators, two type-II integrators, two resonant circuits with gains of K g1 and K g2 , four feedforward paths with gains of K1, K2, K3, and 1, three digital adders, and a delay element z -1 ; One digital adder, one type-I integrator, and one type-II integrator are connected in series to form one branch of a vector filter. The first vector filter branch and the second vector filter branch are formed in this way and connected in series; a resonant circuit with a gain of K is connected between the output end of the type-II integrator and its digital adder of the first vector filter branch. g1 A resonant circuit with a gain of K is connected between the output end of the type-II integrator and its digital adder of the second vector filter branch. g2 The output signals of the type-I integrators and type-II integrators of the two vector filter branches are connected to one digital adder. The output signal of this digital adder is sent to a vector sorter, and the vector sorter is connected to the digital adder of the first vector filter branch through a delay element z. -1 ​ The Sigma-Delta modulator receives an input signal u(t), and the output signal v[n] of the Sigma-Delta modulator is sent to the vector sorter of the DEM circuit. After being processed by the vector filter of the DEM circuit, the vector sorter outputs a signal that is sent to the multi-bit DAC, and the multi-bit DAC outputs a shaped signal r(t); The vector sorter satisfies the following expression at any time t = nT, where n is an arbitrary integer and T is the DAC sampling period: where sv i [n] represents the enable signal of the i-th DAC unit, v[n] is the output of the sigma-delta modulator, and N is the number of unit elements of the DAC.

2. The spectral shaping circuit based on vector filtering DEM according to claim 1, wherein The type-I integrator includes two digital adders, a delay element z -1 , a scalar negative feedback loop with a gain of K * , and a vector-to-scalar adder ∑ VTS . The two digital adders are connected in series and are respectively the first-stage digital adder and the second-stage digital adder according to the signal flow direction. The signal is input from the first-stage digital adder and output from the second-stage digital adder. The vector-to-scalar adder ∑ VTS is led out between the two digital adders and is connected to the second-stage digital adder through the scalar negative feedback loop with a gain of K * . The output terminal of the second-stage digital adder is feedback-connected to the first-stage digital adder through the delay element z -1 .

3. The spectral shaping circuit based on vector filtering DEM according to claim 2, wherein, The type-II integrator includes two digital adders, a delay element z -1 , a scalar negative feedback loop with a gain of K * , and a vector-to-scalar adder ∑ VTS . The two digital adders are connected in series, and are respectively the first-stage digital adder and the second-stage digital adder according to the signal flow direction. The signal is input from the first-stage digital adder and output from the second-stage digital adder. The delay element z -1 is connected between the two digital adders. The vector-to-scalar adder ∑ VTS is led out between the delay element z -1 and the second-stage digital adder and is connected to the second-stage digital adder through the scalar negative feedback loop with a gain of K * . The output end of the second-stage digital adder is feedback-connected to the first-stage digital adder.

4. The spectral shaping circuit based on vector filtering DEM according to claim 3, wherein The gain is K * of K in the scalar negative feedback loop * = 1 / (2^N).

5. The spectrum shaping circuit based on vector filtering DEM according to claim 1, characterized in that The vector sorter in the DEM circuit feeds back to the vector filter in a positive feedback manner.

6. The spectral shaping circuit based on vector filtering DEM according to claim 5, wherein The gain is K g1 The resonant circuit is feedback from the output terminal of the type-II integrator of the first vector filter branch to its digital adder in a negative feedback manner; the gain is K g2 The resonant circuit is feedback from the output terminal of the type-II integrator of the second vector filter branch to its digital adder in a negative feedback manner.

7. The spectrum shaping circuit based on vector filtering DEM according to claim 1, characterized in that If the type-I integrator and type-II integrator in series connection of the first vector filter branch and the second vector filter branch are numbered in sequence, the output of the (i-1)th stage integrator serves as the input of the ith stage integrator; the output signal of the vector sequencer and the output signal of the ith stage integrator are both N-dimensional vectors, where i ≥ 1 and i is an integer.

8. The spectral shaping circuit based on vector filtering DEM according to claim 1, characterized in that The order of the Sigma-Delta modulator is arbitrary.

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