CN117559998A - Thermal noise self-shaping method and system applied to high-precision analog-to-digital converter - Google Patents

Thermal noise self-shaping method and system applied to high-precision analog-to-digital converter Download PDF

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CN117559998A
CN117559998A CN202311674913.7A CN202311674913A CN117559998A CN 117559998 A CN117559998 A CN 117559998A CN 202311674913 A CN202311674913 A CN 202311674913A CN 117559998 A CN117559998 A CN 117559998A
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signal
noise
shaping
filter
digital converter
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刘术彬
田丽
张延博
熊雨舟
付国龙
张祥辉
朱樟明
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Xidian University
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Xidian University
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M1/00—Analogue/digital conversion; Digital/analogue conversion
    • H03M1/06—Continuously compensating for, or preventing, undesired influence of physical parameters
    • H03M1/08—Continuously compensating for, or preventing, undesired influence of physical parameters of noise
    • H03M1/0854—Continuously compensating for, or preventing, undesired influence of physical parameters of noise of quantisation noise
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H17/00—Networks using digital techniques
    • H03H17/02—Frequency selective networks
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M1/00—Analogue/digital conversion; Digital/analogue conversion
    • H03M1/12—Analogue/digital converters
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H17/00—Networks using digital techniques
    • H03H2017/0072—Theoretical filter design
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H17/00—Networks using digital techniques
    • H03H2017/0072—Theoretical filter design
    • H03H2017/0081—Theoretical filter design of FIR filters
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H17/00—Networks using digital techniques
    • H03H2017/0072—Theoretical filter design
    • H03H2017/009—Theoretical filter design of IIR filters

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  • Theoretical Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • Mathematical Physics (AREA)
  • Analogue/Digital Conversion (AREA)

Abstract

The invention provides a thermal noise self-shaping method and a system applied to a high-precision analog-to-digital converter, wherein the method comprises the following steps: judging that noise of the analog-to-digital converter is shaped into a single loop or a cascade structure, if the single loop is selected to be a feedforward structure or a feedback structure, if the cascade structure is selected to be the feedforward structure and/or the feedback structure; constructing an FIR filter as a loop filter in a feed-forward structure, and constructing an IIR filter as a loop filter in a feed-back structure; and constructing a noise transfer function consisting of poles, wherein the number and the positions of the poles are matched with the shaping effect of the noise shaping module. The system comprises a judging module, a construction filter module and a noise shaping module. The invention solves the problem of noise shaping except quantization noise and comparator noise, and realizes noise shaping of introduced noise by reasonably designing a noise shaping NTF module formed by poles, thereby improving shaping efficiency.

Description

Thermal noise self-shaping method and system applied to high-precision analog-to-digital converter
Technical Field
The invention relates to the field of integrated circuit design, in particular to a thermal noise self-shaping method and a thermal noise self-shaping system applied to a high-precision analog-to-digital converter.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
The noise shaping SAR ADC is a hybrid architecture combining the advantages of the SAR ADC and the delta-sigma ADC, and applies the noise shaping technology in the delta-sigma ADC to the SAR ADC, so that the highly digitized circuit structure of the SAR ADC can be maintained, and the shaping of non-ideal factors such as in-band quantization noise, comparator noise and the like can be realized, thereby realizing high precision.
Meanwhile, in the existing noise shaping scheme, the filter is realized in a passive mode or an active mode, the passive mode usually adopts a charge sharing mode, and the circuit behavior of a switch capacitor of the filter can introduce kT/C thermal noise; the active implementation mode generally uses an operational amplifier, and noise sources introduced by the operational amplifier are more diverse, such as transistor thermal noise, resistance thermal noise and the like; more thermal noise is introduced while shaping quantization noise and comparator noise is ensured, the noise can limit the SNR of the whole circuit, and in order to solve the problem of kT/C thermal noise, the influence of the noise on the SNR is limited within the expectations, and the relevant capacitance of a filter needs to be improved, so that on one hand, a larger chip area is occupied, on the other hand, more power consumption is required, and the high-energy efficiency characteristic of the noise shaping SAR ADC is violated.
During high-precision circuit design, noise of a circuit module is generally reasonably distributed and designed, shaping can be realized in a very efficient way for noise except quantization noise and comparator noise, the requirement on a filter can be relaxed under the condition of certain design requirements, and the cost is reduced; better noise characteristics can be further achieved in designs that are currently limited by thermal noise.
Disclosure of Invention
Compared with the traditional noise shaping scheme, the invention can realize noise shaping of the noise introduced by the quantization noise and the filter by reasonably designing a noise shaping NTF (noise transfer function ) module consisting of poles, thereby improving shaping efficiency.
The technical scheme for realizing the purpose of the invention is as follows:
in one aspect, the present invention provides a thermal noise self-shaping method applied to a high-precision analog-to-digital converter, including:
judging the noise shaping form of the analog-to-digital converter, and selecting a corresponding thermal noise self-shaping structure according to the noise shaping form; if the noise is shaped into a single loop, a feedforward structure or a feedback structure is selected as a thermal noise self-shaping structure, and if the noise is shaped into a cascade structure, the feedforward structure and/or the feedback structure is selected as the thermal noise self-shaping structure;
constructing a corresponding loop filter according to the selected thermal noise self-shaping structure; in the single loop or the cascade structure, the loop filter is constructed as an FIR filter in a feedforward structure, and the loop filter is constructed as an IIR filter in a feedback structure;
constructing a transfer function consisting of poles in the loop filter as a noise shaping NTF filter module, and utilizing the noise shaping NTF filter module to realize the self shaping of the thermal noise of the analog-to-digital converter; the noise shaping NTF filtering module is used for matching the shaping effect of the noise shaping NTF module according to the number of the poles and the positions of the poles.
Based on an aspect, in one embodiment of the present invention, the feed-forward structure includes:
summing the Vin signal and the quantization noise Q (z) signal supplied from the analog-to-digital converter with the noise shaping signal to obtain a Dout (z) signal;
obtaining a second signal by differencing the Vin signal and the Dout (z) signal;
and inputting the second signal into the FIR filter to obtain a noise shaping signal.
Based on an aspect, in one embodiment of the present invention, the loop filter constructed in the feedforward structure is an FIR filter, including:
taking the second signal of the feedforward structure as the input of the FIR filter, and introducing the input end of the FIR filter into V n A signal, namely thermal noise introduced by an FIR filter is equivalent to an input end, and the FIR filter outputs the noise shaping signal;
summing the noise-shaped signal, the Vin signal delivered from the analog-to-digital converter, and the quantization noise Q (z) signal to obtain a Dout (z) signal;
transforming a time domain signal into a Z domain signal when the Vin signal is processed by a transfer function H with a coefficient of a, and obtaining a noise shaping signal by an output end of the FIR filter;
wherein, the feedforward structure includes the corresponding operation of FIR filter as:
(V in -D out +V n )×H(z)+V in +Q(z)＝D out (z)
wherein V is in For input signal Vin signal from analog-to-digital converter, V n V for introducing thermal noise into the filter itself n The signal, H (z)/(1+H (z)) is NTF of the thermal noise Vn signal, Q (z) is the quantization noise Q (z) signal, D out (z) is the Dout (z) signal resulting from the summation of the Vin signal, the noise-shaped signal, and the quantization noise Q (z) signal.
On the one hand, in one embodiment of the present invention, constructing a noise shaping NTF module consisting of poles in the loop filter includes:
a delay unit is built in the loop filter, and the circuit implementation mode of the delay unit selects an active mode or a passive mode;
the transfer function of the filter is expressed as:
H(z)＝a n z -n +…+a 2 z -2 +a 1 z -1
where a is a coefficient of a transfer function, the transfer function is H, Z is a time domain transformed to Z domain when processing noise signal, -1, -2 … … -n represents delay;
the matched filter builds a noise shaping NTF module consisting of poles.
Based on an aspect, in one embodiment of the present invention, the feedback structure includes:
summing the Vin signal transmitted from the analog-to-digital converter with the noise shaping signal to obtain a first signal;
summing the first signal and a quantization noise Q (z) signal to obtain a Dout (z) signal;
the Dout (z) signal is input to the feedback structure.
Based on an aspect, in one embodiment of the present invention, constructing an IIR filter in the feedback structure as a loop filter of the single loop or the cascade structure includes:
the Dout (z) signal and the first signal of the feedback structure are subjected to difference to obtain Vin and H signals of the IIR filter;
inputting the Vin and H signals into the IIR filter, and outputting Vout and H signals by the IIR filter;
the Vin signal and the Vout, H signal are input into the noise shaping NTF module in the loop filter to be summed to obtain the first signal;
the thermal noise Vn signal is introduced into the IIR filter, namely the thermal noise introduced into the IIR filter is equivalent to the input end, and the thermal noise Vn signal is input into the IIR filter H (z); the feedback structure comprises the following operation corresponding to the IIR filter:
V in +V n ×H(z)+(-Q(z))×H(z)+Q(z)＝D out (z)
D out (z)＝V in +H(z)·V n +(1-H(z))·Q(z)；
wherein V is in For Vin signal supplied from analog-to-digital converter, V n To introduce a thermal noise Vn signal, H (z) is NTF of the thermal noise Vn signal, Q (z) is quantization noise Q (z) signal, D out (z) is the sum of the Dout (z) signals.
On the one hand, in one embodiment of the present invention, constructing a noise shaping NTF module consisting of poles in the loop filter includes:
constructing an integrator in the loop filter, wherein the implementation mode of the integrator circuit is divided into an active mode or a passive mode;
the loop filter has the expression:
where a is a coefficient of a transfer function, the transfer function is H, Z is a time domain transformed to Z domain when processing noise signal, -1, -2 … … -n represents delay;
the matched integrator builds a noise shaping NTF module consisting of poles.
In another aspect, the present invention provides a thermal noise self-shaping system for a high-precision analog-to-digital converter, comprising:
the judging module judges that the noise of the analog-to-digital converter is shaped into a single loop or a cascade structure, if the noise is shaped into a feedforward structure or a feedback structure by selecting the thermal noise self-shaping structure for the single loop, the noise is shaped into the feedforward structure and/or the feedback structure by selecting the thermal noise self-shaping structure for the cascade structure;
a construction filter module that constructs an FIR filter as a loop filter in the feed-forward structure and constructs an IIR filter as a loop filter in the feed-back structure;
and the noise shaping module is used for constructing a noise shaping NTF module consisting of poles, and the number and the positions of the poles are matched with the shaping effect of the noise shaping NTF module.
Based on another aspect, in one embodiment of the present invention, the feed-forward structure includes: summing the Vin signal, the quantization noise Q (z) signal and the noise shaping signal input from the analog-to-digital converter to obtain a Dout (z) signal; the Vin signal and the Dout (z) signal are subjected to difference to obtain a second signal; a second signal is input into the FIR filter to obtain a noise shaping signal;
constructing an FIR filter as a loop filter in the feed forward structure includes: the second signal is used as the input of the FIR filter, the input end of the FIR filter is introduced with the Vn signal, the Vn signal is the thermal noise introduced by the filter and is equivalent to the input end, and the FIR filter outputs a noise shaping signal; summing the noise shaping signal, the Vin signal and the Q (z) signal to obtain a Dout (z) signal; the transfer function H with the coefficient of a transforms a time domain signal into a Z domain signal when processing the signal, and the FIR filter obtains a noise shaping signal;
wherein, the feedforward structure includes the corresponding operation of FIR filter as:
(V in -D out +V n )×H(z)+V in +Q(z)＝D out (z)
V in for Vin signal supplied from analog-to-digital converter, V n To introduce a thermal noise Vn signal, H (z)/(1+H (z)) is NTF of the thermal noise Vn signal, Q (z) is a quantization noise Q (z) signal, D out (z) is Dout (z) signal obtained by summing Vin signal, noise shaping signal and quantization noise Q (z) signal;
constructing a noise shaping NTF module consisting of poles, comprising: constructing a delay unit, wherein the circuit implementation mode of the delay unit selects an active mode or a passive mode; the transfer function of the filter is expressed as:
H(z)＝a n z -n +…+a 2 z -2 +a 1 z -1
where a is the coefficient of the transfer function and Z is the transform of the time domain into the Z domain when processing the noise signal, -1, -2 … … -n represent the delay.
Based on another aspect, in one embodiment of the present invention, the feedback structure includes:
summing the Vin signal transmitted by the analog-to-digital converter with the noise shaping signal to obtain a first signal; summing the first signal and the Q (z) signal to obtain a Dout (z) signal; the Dout (z) signal is input to the feedback structure;
constructing an IIR filter as a loop filter in the feedback structure includes: summing the Dout (z) signal and the first signal to obtain Vin and H signals; vin and H signals are input into an IIR filter, and the IIR filter outputs Vout and H signals; summing the Vin signal with the Vout and H signals to obtain a first signal; the IIR filter introduces a thermal noise Vn signal, and a noise shaping NTF module of the thermal noise Vn signal is H (z); the feedback structure comprises operations corresponding to the IIR filter, including:
V in +V n ×H(z)+(-Q(z))×H(z)+Q(z)＝D out (z)
D out (z)＝V in +H(z)·V n +(1-H(z))·Q(z)；
V in for Vin signal supplied from analog-to-digital converter, V n To introduce a thermal noise Vn signal, H (z) is NTF of the thermal noise Vn signal, Q (z) is Q (z) signal summed with the first signal, D out (z) is the summed Dout (z) signal;
constructing a noise shaping NTF module consisting of poles, comprising: constructing an integrator, wherein the integrator circuit realizes the selection of an active mode or a passive mode; the transfer function expression of the integrator is:
where H is the transfer function, a is the coefficient of the transfer function, Z is the transform of the time domain into the Z domain when processing the noise signal, -1, -2 … … -n represent the delay.
Compared with the prior art, the invention has the beneficial effects that:
compared with the traditional noise shaping scheme, the noise shaping method solves the problem of noise shaping except quantization noise and comparator noise, and can realize noise shaping of the quantization noise and noise introduced by the filter by reasonably designing the noise shaping NTF module consisting of poles, thereby improving shaping efficiency.
Drawings
Fig. 1 is a flowchart of a thermal noise self-shaping method applied to a high-precision analog-to-digital converter according to an embodiment of the present invention;
fig. 2 is a signal flow diagram of a feedback structure according to an embodiment of the present invention;
FIG. 3 is a signal flow diagram of the thermal noise introduced in FIG. 2;
FIG. 4 is a signal flow diagram of a feedforward architecture according to an embodiment of the present invention;
FIG. 5 is a signal flow diagram of the thermal noise introduced in FIG. 4;
FIG. 6 is a table comparing the idealities provided by the present embodiment with the thermal noise added to the filter;
fig. 7 is a system SQNR change list corresponding to different NTFs when two coefficients of the NTFs provided in the embodiment of the present invention fluctuate by 10%;
FIG. 8 is a table of relationships between OSR and SQNR based on NTF provided by an embodiment of the present invention;
fig. 9 is a diagram of a 9-bit noise shaping SAR ADC according to an embodiment of the invention.
Detailed Description
The present invention will be described in detail below with reference to the embodiments shown in the drawings, but it should be understood that the embodiments are not limited to the present invention, and functional, method, or structural equivalents and alternatives according to the embodiments are within the scope of protection of the present invention by those skilled in the art.
Example 1:
referring to fig. 1, fig. 1 is a flowchart of a thermal noise self-shaping method applied to a high-precision analog-to-digital converter according to an embodiment of the present invention, where the thermal noise self-shaping method applied to the high-precision analog-to-digital converter includes:
judging the noise shaping form of the analog-to-digital converter, if the noise shaping is a single loop, selecting a thermal noise self-shaping structure as a feedforward structure or a feedback structure, and if the noise shaping is a cascade structure, selecting the thermal noise self-shaping structure as a feedforward structure and/or a feedback structure;
constructing a corresponding loop filter according to the selected thermal noise self-shaping structure; in a single loop or cascade structure, the loop filter is constructed as an FIR filter in a feedforward structure, and the loop filter is constructed as an IIR filter in a feedback structure;
and constructing a transfer function consisting of poles in the loop filter as a noise shaping NTF module (noise transfer function ) module, and matching the shaping effect of the noise shaping NTF module according to the number of the poles and the positions of the poles.
The cascade structure of the embodiment of the invention is a cascade structure of a plurality of loops, each loop selects a feedforward structure or a feedback structure, and the loops can all correspond to the feedforward structure or the feedback structure, and of course, a part of the loops can also be the feedforward structure, and the other part of the loops are the feedback structure.
Referring to fig. 2, fig. 2 is a signal flow diagram of a feedback structure provided by an embodiment of the present invention, where in the feedback structure, a first signal is obtained by summing a Vin signal transmitted by an analog-to-digital converter and a noise shaping signal; summing the first signal and the quantization noise Q (z) signal to obtain a Dout (z) signal; the Dout (z) signal is output to a feedback structure.
Referring to fig. 3, fig. 3 is a signal flow diagram of thermal noise introduced in fig. 2, where the above-mentioned loop filter configured as a single loop or a cascade structure in a feedback structure includes: the Dout (z) signal of the feedback structure is differenced with the first signal to obtain Vin and H signals of the IIR filter; vin and H signals are input into an IIR filter, and Vout and H signals are output by the IIR filter; summing the Vin signal and the Vout, and summing the H signal by a noise shaping (NTF) module in a loop filter to obtain a first signal; the thermal noise Vn signal is introduced into the IIR filter, and is input to the IIR filter H (z); the feedback structure comprises the following operation corresponding to the IIR filter:
V in +V n ×H(z)+(-Q(z))×H(z)+Q(z)＝D out (z)
D out (z)＝V in +H(z)·V n +(1-H(z))·Q(z)；
wherein V is in For Vin signal supplied from analog-to-digital converter, V n To introduce a thermal noise Vn signal, H (z) is NTF of the thermal noise Vn signal, Q (z) is quantization noise Q (z) signal, D out (z) is the sum of the Dout (z) signals.
The above-mentioned constructing a noise shaping NTF module consisting of poles in a loop filter includes: the loop filter is realized by constructing an integrator, and the realization mode of an integrator circuit is divided into an active mode or a passive mode; the loop filter is expressed as:
where H is the transfer function, a is the coefficient of the transfer function, Z is the transform of the time domain into the Z domain when processing the noise signal, -1, -2 … … -n represent the delay.
Referring to fig. 4, fig. 4 is a signal flow diagram of a feedforward structure according to an embodiment of the present invention, where the feedforward structure includes: summing the Vin signal and the quantization noise Q (z) signal supplied from the analog-to-digital converter with the noise shaping signal to obtain a Dout (z) signal; the Vin signal and the Dout (z) signal are subjected to difference to obtain a second signal; the second signal is input to the FIR filter to obtain a noise shaped signal.
Referring to fig. 5, fig. 5 is a signal flow diagram of introducing thermal noise in fig. 4, where the loop filter is configured as an FIR filter in the feedforward structure, and includes: taking the second signal with the feedforward structure as the input of the FIR filter, and introducing the input end of the FIR filter into V n The signal, the FIR filter outputs the noise shaping signalA number; summing the noise-shaped signal, the Vin signal transmitted from the analog-to-digital converter and the quantization noise Q (z) signal to obtain a Dout (z) signal; the transfer function H with the coefficient of a transforms a time domain signal into a Z domain signal when processing a Vin signal, and the FIR filter obtains a noise shaping signal; the feedforward structure includes the corresponding operation of the FIR filter as follows:
(V in -D out +V n )×H(z)+V in +Q(z)＝D out (z)
V in for input signal Vin signal from analog-to-digital converter, V n V for introducing thermal noise into the filter itself n The signal, H (z)/(1+H (z)) is NTF of the thermal noise Vn signal, Q (z) is the quantization noise Q (z) signal, D out (z) is the Dout (z) signal resulting from the summation of the Vin signal, the noise-shaped signal, and the quantization noise Q (z) signal.
The above-mentioned constructing a noise shaping NTF module consisting of poles in a loop filter includes: a delay unit is built in the loop filter, and the circuit implementation mode of the delay unit selects an active mode or a passive mode; the transfer function of the filter is expressed as:
H(z)＝a n z -n +…+a 2 z -2 +a 1 z -1
where a is the coefficient of the transfer function, the transfer function is H, Z is the time domain transformed to Z domain when processing the noise signal, -1, -2 … … -n represents the delay.
Compared with the traditional noise shaping scheme, the thermal noise self-shaping method applied to the high-precision analog-to-digital converter provided by the embodiment of the invention has the advantages that the quantization noise and the noise introduced by the filter can be realized with the same shaping efficiency by reasonably designing the NTF and consisting of poles, so that the deterioration of the thermal noise introduced by the filter on the whole system performance can be obviously reduced, the higher noise shaping efficiency is realized, the thermal noise self-shaping method provided by the embodiment of the invention can be widely applied to the noise shaping successive approximation type analog-to-digital converter, and the number and the position of the poles are related to the shaping effect of the NTF.
In practical applications, there are two methods for implementing thermal noise self-shaping in the embodiment of the present invention, one is to construct an IIR filter in a feedback (EF) structure. The second approach is to construct the FIR filter in a feed forward (CIFF) structure. Referring to fig. 2, fig. 2 is a signal flow diagram of a feedback structure provided by an embodiment of the present invention, and the noise shaping mode of fig. 2 is a feedback type, wherein a transfer function H (z) of a filter is configured as an IIR filter, and thermal noise is implemented by an integrator in a circuit of a self-shaping system.
Referring to fig. 3, fig. 3 is a signal flow diagram of thermal noise introduced in fig. 2, and the implementation of the IIR filter constructed by the transfer function H (z) is divided into a passive mode and an active mode. The associated switched capacitor circuits, op-amp circuits, etc. introduce thermal noise. Analysis of a signal flow graph containing thermal noise may yield:
V in +V n ×H(z)+(-Q(z))×H(z)+Q(z)＝D out (z)
D out (z)＝V in +H(z)·V n +(1-H(z))·Q(z)
thermal noise V introduced for IIR filter n Its NTF is H (z).
Referring to fig. 4, fig. 4 is a signal flow diagram of a feedforward structure provided by an embodiment of the present invention, wherein a noise shaping manner is feedforward, and a transfer function H (z) of a filter is configured as an FIR filter, and a circuit-level behavior manner can be implemented only by a delay unit.
Since the transfer function of the FIR filter does not require integration, the noise of the filter can be equivalent to the input or output for analysis, whether in a passive or active implementation. Referring to fig. 5, fig. 5 is a signal flow diagram of fig. 4 in which thermal noise is introduced, the noise introduced by the filter is labeled in fig. 5, V in the figure n Representing thermal noise that may be introduced into the circuit, analyzing the entire signal flow graph may yield a relationship:
(V in -D out +V n )×H(z)+V in +Q(z)＝D out (z)
in the feedforward structure, the loop filter is designed as an FIR filter, and the thermal noise introduced by the input and output of the FIR filter can be shaped, and the shaping effect is equivalent to that of the quantization noise. The FIR filter of the embodiment of the invention is also added with a delay unit, and the delay unit is simpler and more convenient than an integrator required by the implementation of the IIR filter.
Taking a 9-bit noise shaping SAR ADC as an example, when osr=6, two NTFs capable of achieving the same quantization noise shaping are taken as comparison descriptions, please refer to fig. 6, fig. 6 is a comparison table of ideal case and filter thermal noise added provided in the embodiment of the present invention, fig. 6As can be seen from fig. 6, after thermal noise is introduced, the overall SNDR is reduced, and for two NTF filters capable of producing the same quantization noise shaping effect, the thermal noise shaping method provided by the embodiment of the present invention has an obvious effect, and when thermal noise shaping is not performed, the SNDR is limited to the level of thermal noise, and after thermal noise shaping is introduced, the SNDR is improved by 5.463dB. The NTF filter matches circuit indexes and meets the requirements of the whole system on noise.
According to the thermal noise self-shaping method, the NTF filter is relatively insensitive to the coefficient, when the NTF coefficient is designed, an active operational amplifier is needed for the realization of the thermal noise self-shaping system, the characteristic of the active operational amplifier is relatively sensitive to PVT variation, so that the NTF coefficient is offset, the shaping efficiency is influenced by the offset of the NTF coefficient in the traditional thermal noise shaping, and the shaping effect of quantization noise is limited while the thermal noise of the filter is introduced. The NTF provided by the embodiment of the invention is composed of poles, and when the coefficient of the NTF fluctuates to a certain extent, the amplitude-frequency characteristic of the NTF composed of the poles does not change greatly.
Referring to fig. 7, fig. 7 shows a table of system SQNR changes corresponding to different NTFs when two coefficients of the NTF fluctuate by 10%, and as can be seen from fig. 7, when the coefficient of the NTF fluctuates, the SNDR changes by not more than 1dB, which has good robustness.
Usually, the characteristics of the NTF are related to the value of the OSR, and an optimal OSR exists corresponding to the NTF, so that the thermal noise self-shaping method provided by the embodiment of the invention is low in the shaping efficiency of the NTF and the value of the OSR, and is also applicable to the case of low value of the OSR. Since increasing the oversampling rate typically limits the bandwidth, low OSR is suitable for high speed analog to digital converter applications. Referring to fig. 8, fig. 8 is a table showing relationships between OSR and SQNR based on NTF provided in an embodiment of the present invention,
for the NTF illustrated in the present invention, a table of the relationship between the OSR and the system SQNR is given, and it can be seen from the table in fig. 8 that the system SQNR is improved by 3dB for each time the OSR is improved by one time.
The thermal noise self-shaping method provided by the embodiment of the invention realizes shaping of the quantization noise and the comparator noise and simultaneously shapes the thermal noise of the filter, so that the method does not introduce additional thermal noise and has higher energy efficiency compared with the traditional scheme. The loop filter is designed to be FIR in a feedforward structure or IIR in a feedback structure, and the NTF consisting of poles is constructed. Meanwhile, the NTF formed by poles is insensitive to coefficients, so that the design requirement on a filter is further relaxed, and the NTF has good robustness.
Example 2:
on the basis of the scheme disclosed in embodiment 1, the embodiment of the invention provides a thermal noise self-shaping system applied to a high-precision analog-to-digital converter, which comprises the following components:
the judging module judges that the noise of the analog-to-digital converter is shaped into a single loop or a cascade structure, if the noise is shaped into a feedforward structure or a feedback structure by selecting the thermal noise self-shaping structure for the single loop, if the noise is shaped into the feedforward structure and/or the feedback structure by selecting the thermal noise self-shaping structure for the cascade structure;
a construction filter module which constructs an FIR filter as a loop filter in a feed-forward structure and constructs an IIR filter as a loop filter in a feed-back structure;
and the noise shaping module is used for constructing a noise shaping NTF module consisting of poles, and the number and the positions of the poles are matched with the shaping effect of the noise shaping NTF module.
The feedback structure described above includes:
summing the Vin signal transmitted by the analog-to-digital converter with the noise shaping signal to obtain a first signal; summing the first signal and the Q (z) signal to obtain a Dout (z) signal; the Dout (z) signal is input into a feedback structure;
constructing an IIR filter as a loop filter in a feedback structure includes: summing the Dout (z) signal and the first signal to obtain Vin and H signals; vin and H signals are input into an IIR filter, and the Vout and H signals are output by the FIR filter; summing the Vin signal with the Vout and H signals to obtain a first signal; the IIR filter introduces a thermal noise Vn signal, and a noise shaping NTF module of the thermal noise Vn signal is H (z); the operation of the IIR filter includes:
V in +V n ×H(z)+(-Q(z))×H(z)+Q(z)＝D out (z)
D out (z)＝V in +H(z)·V n +(1-H(z))·Q(z)；
V in for Vin signal supplied from analog-to-digital converter, V n To introduce a thermal noise Vn signal, H (z) is NTF of the thermal noise Vn signal, Q (z) is Q (z) signal summed with the first signal, D out (z) is the summed Dout (z) signal;
constructing a noise shaping NTF module consisting of poles, comprising: constructing an integrator, wherein the implementation mode of the integrator circuit is divided into an active mode or a passive mode; the loop filter is expressed as:
where H is the transfer function, a is the coefficient of the transfer function, Z is the transform of the time domain into the Z domain when processing the noise signal, -1, -2 … … -n represent the delay.
The feedforward structure includes: summing the Vin signal, the Q (z) signal and the noise shaping signal which are transmitted by the analog-to-digital converter to obtain a Dout (z) signal; summing the Vin signal and the Dout (z) signal to obtain a second signal; the second signal is input into an FIR filter to obtain a noise shaping signal;
constructing an FIR filter as a loop filter in a feed forward structure includes: the second signal is used as the input of the FIR filter, the input end of the FIR filter is introduced with the Vn signal, and the FIR filter outputs the noise shaping signal; summing the noise shaping signal, the Vin signal and the Q (z) signal to obtain a Dout (z) signal; the transfer function H with the coefficient of a transforms a time domain signal into a Z domain signal when processing the signal, and the FIR filter obtains a noise shaping signal;
the feedforward structure includes the corresponding operation of the FIR filter as follows:
(V in -D out +V n )×H(z)+V in +Q(z)＝D out (z)
V in for input signal Vin signal from analog-to-digital converter, V n Introducing a thermal noise Vn signal into the filter itself, H (z)/(1+h (z)) being the NTF of the thermal noise Vn signal, Q (z) being the Q (z) signal summed with the first signal, D out (z) is the sum of the Dout (z) signals.
Constructing a noise shaping NTF module consisting of poles, comprising: a delay unit is built in the loop filter, and the circuit implementation mode of the delay unit selects an active mode or a passive mode; the transfer function of the filter is expressed as:
H(z)＝a n z -n +…+a 2 z -2 +a 1 z -1
where a is the coefficient of the transfer function and Z is the transform of the time domain into the Z domain when processing the noise signal, -1, -2 … … -n represent the delay.
Compared with the traditional noise shaping scheme, the embodiment of the invention can realize noise shaping of the quantization noise and the noise introduced by the filter by reasonably designing the noise shaping NTF module consisting of poles, thereby improving shaping efficiency.
The above list of detailed descriptions is only specific to practical embodiments of the present invention, and they are not intended to limit the scope of the present invention, and all equivalent embodiments or modifications that do not depart from the spirit of the present invention should be included in the scope of the present invention.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.
Furthermore, it should be understood that although the present disclosure describes embodiments, not every embodiment is provided with a separate embodiment, and that this description is provided for clarity only, and that the disclosure is not limited to the embodiments described in detail below, and that the embodiments described in the examples may be combined as appropriate to form other embodiments that will be apparent to those skilled in the art.

Claims (10)

1. A thermal noise self-shaping method applied to a high-precision analog-to-digital converter, comprising:
judging the noise shaping form of the analog-to-digital converter, and selecting a corresponding thermal noise self-shaping structure according to the noise shaping form; if the noise is shaped into a single loop, a feedforward structure or a feedback structure is selected as a thermal noise self-shaping structure, and if the noise is shaped into a cascade structure, the feedforward structure and/or the feedback structure is selected as the thermal noise self-shaping structure;
constructing a corresponding loop filter according to the selected thermal noise self-shaping structure; in the single loop or the cascade structure, the loop filter is constructed as an FIR filter in a feedforward structure, and the loop filter is constructed as an IIR filter in a feedback structure;
constructing a transfer function consisting of poles in the loop filter as a noise shaping NTF filter module, and utilizing the noise shaping NTF filter module to realize the self shaping of the thermal noise of the analog-to-digital converter; the noise shaping NTF filtering module is used for matching the shaping effect of the noise shaping NTF module according to the number of the poles and the positions of the poles.
2. The method for self-shaping thermal noise applied to high-precision analog-to-digital converter according to claim 1, wherein said feedforward structure comprises:
summing the Vin signal and the quantization noise Q (z) signal supplied from the analog-to-digital converter with the noise shaping signal to obtain a Dout (z) signal;
obtaining a second signal by differencing the Vin signal and the Dout (z) signal;
and inputting the second signal into the FIR filter to obtain a noise shaping signal.
3. The method for self-shaping thermal noise applied to high-precision analog-to-digital converter according to claim 2, wherein the loop filter constructed in the feedforward structure is an FIR filter, comprising:
taking the second signal of the feedforward structure as the input of the FIR filter, and introducing the input end of the FIR filter into V n A signal, the FIR filter outputs the noise shaping signalA number;
summing the noise-shaped signal, the Vin signal delivered from the analog-to-digital converter, and the quantization noise Q (z) signal to obtain a Dout (z) signal;
transforming a time domain signal into a Z domain signal when the Vin signal is processed by a transfer function H with a coefficient of a, and obtaining a noise shaping signal by an output end of the FIR filter;
wherein, the feedforward structure includes the corresponding operation of FIR filter as:
(V in -D out +V n )×H(z)+V in +Q(z)＝D out (z)
V in is the input signal Vin signal of the analog-to-digital converter, V n V for introducing thermal noise into the filter itself n The signal, H (z)/(1+H (z)) is NTF of the thermal noise Vn signal, Q (z) is the quantization noise Q (z) signal, D out (z) is the Dout (z) signal resulting from the summation of the Vin signal, the noise-shaped signal, and the quantization noise Q (z) signal.
4. A thermal noise self-shaping method applied to a high precision analog to digital converter as claimed in claim 3, wherein constructing a noise shaping NTF module consisting of poles in said loop filter comprises:
a delay unit is built in the loop filter, and the circuit implementation mode of the delay unit selects an active mode or a passive mode;
the transfer function of the filter is expressed as:
H(z)＝a n z -n +…+a 2 z -2 +a 1 z -1
where a is a coefficient of a transfer function, the transfer function is H, Z is a time domain transformed to Z domain when processing noise signal, -1, -2 … … -n represents delay;
the matched filter builds a noise shaping NTF module consisting of poles.
5. The method for self-shaping thermal noise applied to a high-precision analog-to-digital converter according to claim 1, wherein said feedback structure comprises:
summing the Vin signal transmitted from the analog-to-digital converter with the noise shaping signal to obtain a first signal;
summing the first signal and a quantization noise Q (z) signal to obtain a Dout (z) signal;
the Dout (z) signal is input to the feedback structure.
6. A thermal noise self-shaping method applied to a high precision analog to digital converter as claimed in claim 5, wherein constructing an IIR filter in said feedback structure as a loop filter of said single loop or said cascade structure comprises:
the Dout (z) signal and the first signal of the feedback structure are subjected to difference to obtain Vin and H signals of the IIR filter;
inputting the Vin and H signals into the IIR filter, and outputting Vout and H signals by the IIR filter;
summing the Vin signal and the Vout, H signal to obtain the first signal;
the thermal noise Vn signal is input to an IIR filter H (z); the feedback structure comprises the following operation corresponding to the IIR filter:
V in +V n ×H(z)+(-Q(z))×H(z)+Q(z)＝D out (z)
D out (z)＝V in +H(z)·V n +(1-H(z))·Q(z)；
wherein V is in For Vin signal supplied from analog-to-digital converter, V n To introduce a thermal noise Vn signal, H (z) is NTF of the thermal noise Vn signal, Q (z) is quantization noise Q (z) signal, D out (z) is the sum of the Dout (z) signals.
7. A thermal noise self-shaping method applied to a high precision analog to digital converter as claimed in claim 1, wherein constructing a noise shaping NTF module consisting of poles in the loop filter comprises:
an integrator is built in the loop filter, and the implementation mode of the integrator circuit is divided into an active mode or a passive mode;
the loop filter has the expression:
where a is the coefficient of transfer function, H is transfer function, Z is the time domain transformed to Z domain when processing noise signal, -1, -2 … … -n represents delay;
the matched integrator builds a noise shaping NTF module consisting of poles.
8. A thermal noise self-shaping system for a high-precision analog-to-digital converter, comprising:
the judging module judges that the noise of the analog-to-digital converter is shaped into a single loop or a cascade structure, if the noise is shaped into a feedforward structure or a feedback structure by selecting the thermal noise self-shaping structure for the single loop, the noise is shaped into the feedforward structure and/or the feedback structure by selecting the thermal noise self-shaping structure for the cascade structure;
a construction filter module that constructs an FIR filter as a loop filter in the feed-forward structure and constructs an IIR filter as a loop filter in the feed-back structure;
and the noise shaping module is used for constructing a noise shaping NTF module consisting of poles, and the number and the positions of the poles are matched with the shaping effect of the noise shaping NTF module.
9. The thermal noise self-shaping system for a high precision analog to digital converter of claim 8, wherein said feed forward structure comprises: summing the Vin signal, the quantization noise Q (z) signal and the noise shaping signal input from the analog-to-digital converter to obtain a Dout (z) signal; the Vin signal and the Dout (z) signal are subjected to difference to obtain a second signal; a second signal is input into the FIR filter to obtain a noise shaping signal;
constructing an FIR filter as a loop filter in the feed forward structure includes: the second signal is used as the input of the FIR filter, the input end of the FIR filter is introduced with the Vn signal, the Vn signal is the thermal noise introduced by the filter and is equivalent to the input end, and the FIR filter outputs a noise shaping signal; summing the noise shaping signal, the Vin signal and the Q (z) signal to obtain a Dout (z) signal; the transfer function H with the coefficient of a transforms a time domain signal into a Z domain signal when processing the signal, and the FIR filter obtains a noise shaping signal;
wherein, the feedforward structure includes the corresponding operation of FIR filter as:
(V in -D out +V n )×H(z)+V in +Q(z)＝D out (z)
V in for Vin signal supplied from analog-to-digital converter, V n To introduce a thermal noise Vn signal, H (z) is NTF of the thermal noise Vn signal, Q (z) is Q (z) signal summed with the first signal, D out (z) is the summed Dout (z) signal;
constructing a noise shaping NTF module consisting of poles, comprising: the circuit implementation mode of the delay unit selects an active mode or a passive mode; the transfer function of the filter is expressed as:
H(z)＝a n z -n +…+a 2 z -2 +a 1 z -1
where a is the coefficient of the transfer function and Z is the transform of the time domain into the Z domain when processing the noise signal, -1, -2 … … -n represent the delay.
10. The thermal noise self-shaping system for a high precision analog to digital converter of claim 8, wherein said feedback structure comprises:
summing the Vin signal transmitted by the analog-to-digital converter with the noise shaping signal to obtain a first signal; summing the first signal and the Q (z) signal to obtain a Dout (z) signal; the Dout (z) signal is input to the feedback structure;
constructing an IIR filter as a loop filter in the feedback structure includes: summing the Dout (z) signal and the first signal to obtain Vin and H signals; vin and H signals are input into an IIR filter, and the IIR filter outputs Vout and H signals; summing the Vin signal with the Vout and H signals to obtain a first signal; the IIR filter introduces a thermal noise Vn signal, and the noise shaping NTF of the thermal noise Vn signal is H (z); the feedback structure comprises operations corresponding to the IIR filter, including:
V in +V n ×H(z)+(-Q(z))×H(z)+Q(z)＝D out (z)
D out (z)＝V in +H(z)·V n +(1-H(z))·Q(z)；
V in for Vin signal supplied from analog-to-digital converter, V n To introduce a thermal noise Vn signal, H (z) is NTF of the thermal noise Vn signal, Q (z) is Q (z) signal summed with the first signal, D out (z) is the summed Dout (z) signal;
constructing a noise shaping NTF module consisting of poles, comprising: constructing an integrator, wherein the integrator circuit realizes the selection of an active mode or a passive mode; the transfer function expression of the integrator is:
where H is the transfer function, a is the coefficient of the transfer function, Z is the transform of the time domain into the Z domain when processing the noise signal, -1, -2 … … -n represent the delay.
CN202311674913.7A 2023-12-07 2023-12-07 Thermal noise self-shaping method and system applied to high-precision analog-to-digital converter Pending CN117559998A (en)

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