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CN102226822A - RC constant measuring method of differential capacitance - Google Patents

RC constant measuring method of differential capacitance Download PDF

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Publication number
CN102226822A
CN102226822A CN2011100821457A CN201110082145A CN102226822A CN 102226822 A CN102226822 A CN 102226822A CN 2011100821457 A CN2011100821457 A CN 2011100821457A CN 201110082145 A CN201110082145 A CN 201110082145A CN 102226822 A CN102226822 A CN 102226822A
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Prior art keywords
constant
search
differential capacitance
circuit
rcout
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Chinese (zh)
Inventor
李正平
刘松艳
黄伟朝
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Guangzhou Runxin Information Technology Co Ltd
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Guangzhou Runxin Information Technology Co Ltd
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Abstract

The invention discloses an RC (resistance capacitance) constant measuring method of differential capacitance. The method provided by the invention is based on a circuit structure of which differential capacitance is an RC constant, converts the RC constant into a pulse width, and uses a digital circuit to measure the RC constant of the differential capacitance. The method measures the RC constant of the differential capacitance and corrects the same in a circuit, and the method can be widely used in the field of measurement and correction on the RC constant of the differential capacitance better. A measuring module circuit simply implements the conversion between the RC constant and an RC out voltage value, so that the condition for measuring and correcting the RC constant through the digital circuit is provided, the digital circuit can flexibly and conveniently correct the RC constant, and the correction speed is greatly improved through a binary search algorithm.

Description

A kind of RC constant measuring method of differential capacitance
Technical field
The present invention relates to a kind of RC constant measuring method, generally be applied to small resistance capacitive constant product and detect, as detection RC constant value size in the analog filter and to its circuit arrangement of effectively proofreading and correct based on the differential capacitance circuit structure.
Background technology
At present, in Design of Analog Filter, the corner frequency of wave filter, the product of it and resistance capacitance is inversely proportional to.To specific wave filter, its RC constant should be constant.On the sheet integrated wave filter generally be divided into Active RC (resistance capacitance) and
Figure 184872DEST_PATH_IMAGE002
(transconductance capacitor) two kinds of structures.
Figure 39695DEST_PATH_IMAGE002
The general resistance that uses made when structure realized mutual conductance
Figure 819433DEST_PATH_IMAGE004
Because resistance capacitance generally has 10%～25% deviation on the sheet, the corner frequency that influences wave filter is up to ± 50%.Need proofread and correct the corner frequency of wave filter, make its deviation less than ± 5%, transitional zone and the outer inhibition of band just can meet the demands.We generally use switch resistance or switching capacity to realize the filter frequencies correction, the difference with the structure of wave filter realization.The general switched capacitor array that uses in the Active RC wave filter, and The general switched capacitor array that uses in the wave filter, Principles of Regulation are in full accord, and therefore, the correction of wave filter need be done to measure accurately to the RC constant.
The measuring method of RC constant is a lot, for different RC constant structures, can adopt no measuring method.At above-mentioned general RC constant circuit version difference, exist than large deviation, need to reduce error, the accurate problem of measuring, the present invention is based on the circuit structure that differential capacitance is the RC constant, the RC constant is converted to pulse width, adopt digital circuit and realize a kind of be the measuring method of RC constant at differential capacitance.
Summary of the invention
The object of the present invention is to provide a kind of circuit structure simple, it is accurately convenient to measure, the RC constant measuring method of the differential capacitance that precision is controlled.
For solving the problems of the technologies described above, the technical solution used in the present invention is: a kind of RC constant measuring method of differential capacitance, comprise the differential capacitance circuit module and
Figure 966697DEST_PATH_IMAGE006
Measurement module;
Described differential capacitance circuit module act as realize RC constant and comparer export the RCOUT time span (
Figure 789160DEST_PATH_IMAGE006
) proportionate relationship, the conversion of the concrete duty of circuit and
Figure 993876DEST_PATH_IMAGE006
Be calculated as follows:
1) at t0 constantly, switch S 1 closure, reset circuit, at this moment , RCOUT is output as low, because of
Figure 799338DEST_PATH_IMAGE010
, flow through resistance R 1 electric current and be:
， （1）
2) at t1 constantly, switch S 1 disconnects, and reseting procedure finishes, and flows through resistance R 1 electric current I by C1, has:
Figure 547031DEST_PATH_IMAGE014
, release:
Figure 221726DEST_PATH_IMAGE016
Have
Figure 745111DEST_PATH_IMAGE018
, (2)
This moment output voltage
Figure 112639DEST_PATH_IMAGE020
Descend, finally cause
Figure 354264DEST_PATH_IMAGE022
, the comparer output switching activity, RCOUT transfers high level to by low level, is disconnected to the RCOUT level by switch S 1 and uprises this process, and the time is:
Figure 629388DEST_PATH_IMAGE024
，（3）
If fixed coefficient is ,
Figure 542779DEST_PATH_IMAGE028
,
Figure 209383DEST_PATH_IMAGE030
,
Figure 288198DEST_PATH_IMAGE032
, then , (4)
By formula (3) as can be known,
Figure DEST_PATH_IMAGE035
Be directly proportional with the RC constant, it is right that the measurement of RC constant is converted into
Figure 495505DEST_PATH_IMAGE035
Measurement;
Described
Figure 383827DEST_PATH_IMAGE006
Measurement module, RCOUT time measurement module are realized by digital circuit, can carry out the pulse width counting to the RCOUT time constant by the digital dock of using upper frequency, suppose that the digital reference clock is
Figure DEST_PATH_IMAGE037
, count value is N, so
Figure DEST_PATH_IMAGE039
，（5）
Measuring accuracy is by digital dock frequency decision, calculates the RC constant at last to be:
Figure DEST_PATH_IMAGE041
，（6）。
The present invention also comprises the correction of RC circuit, and trimming process was divided into for two steps: initialization and search correction (;
During initialization, send the RC constant
Figure 204015DEST_PATH_IMAGE006
The correction power on signal (PWR_RCTUNE) of measurement module circuit and reset switch signal (RST), power on signal shifts to an earlier date some cycles than reset switch signal, promptly begins the CNT rolling counters forward after the reset switch signal is sent;
The search timing can get the preset reference count value by formula (6)
Figure DEST_PATH_IMAGE043
, realize measuring actual N value and reference by the digital dock of using upper frequency
Figure DEST_PATH_IMAGE045
Value relatively according to comparative result and adjust capacitor array, changes RC value size, up to making the RC value the biglyyest near default R1*C1 value.
Described differential capacitance is made adjustable array format, and binary search algorithm is used in the capacitor array adjustment.
Described binary search algorithm is divided into 3 stages: initialization, search downwards, about search;
1) during initialization, the extreme higher position 1 of switched capacitor array, other position 0 makes its value of mediating.Pulse width (RCOUT) to the output of differential capacitance circuit is counted;
When 2) searching for downwards, count value is judged, if less than preset value, is shown that then current capacitance is less than normal, this moment current search invariant position (being 1), next searching position 1; Otherwise show that capacitance is bigger than normal, current search position 0 begin to search for behind next searching position 1 next time, is determined until the lowest order direction;
When searching for 3), about the definite capacitor array of downward search procedure, search for, determine setting left and right, counting error minimum in first three state;
Suppose that capacitor array has the N position, then need N+2 search altogether, each search time is all identical.
Beneficial effect of the present invention: this method has realized the measurement of differential capacitance RC constant and the correction in circuit thereof.The differential capacitance circuit module has been realized the conversion of RC constant and RCOUT magnitude of voltage simply, measures and proofread and correct the condition that provides for adopting digital circuit, and it is convenient, flexible that digital circuit is proofreaied and correct the RC constant, and binary search algorithm is improved correction rate significantly.
Description of drawings
Fig. 1 is differential capacitance RC constant metering circuit figure.
Fig. 2 is a RCOUT(RCOUT voltage) the measurement sequential chart.
Fig. 3 is a RC constant digital calibration logic diagram.
Fig. 4 is a RC constant digital calibration sequential chart.
Fig. 5 is the binary search algorithm state transition diagram.
Embodiment
Below in conjunction with accompanying drawing the specific embodiment of the present invention is described in further detail.
As depicted in figs. 1 and 2, the RC constant measuring method of a kind of differential capacitance of the present invention comprises differential capacitance circuit module 106 Hes
Figure 431865DEST_PATH_IMAGE006
Measurement module 201;
Described differential capacitance circuit module 106 act as realize RC constant and comparer export the RCOUT time span (
Figure 312097DEST_PATH_IMAGE006
) proportionate relationship, the conversion of the concrete duty of circuit and
Figure 750031DEST_PATH_IMAGE006
Be calculated as follows:
At t0 constantly, switch S 1101 closures, reset circuit, at this moment
Figure 99542DEST_PATH_IMAGE008
, RCOUT is output as low, because of , flow through resistance R 1102 electric currents and be:
Figure DEST_PATH_IMAGE046
， （1）
At t1 constantly, switch S 1101 disconnects, and reseting procedure finishes, and flows through resistance R 1102 electric current I by C1103, has:
, release:
Figure DEST_PATH_IMAGE047
Have , (2)
This moment output voltage Descend, finally cause
Figure 710466DEST_PATH_IMAGE022
, comparer 105 output switching activities, RCOUT transfers high level to by low level, is disconnected to the RCOUT level by switch S 1101 and uprises this process, and the time is:
Figure 771963DEST_PATH_IMAGE024
，（3）
If fixed coefficient is
Figure DEST_PATH_IMAGE049
,
Figure 993997DEST_PATH_IMAGE028
,
Figure 344207DEST_PATH_IMAGE030
,
Figure DEST_PATH_IMAGE050
, then
Figure 372206DEST_PATH_IMAGE034
, (4)
By formula as can be known, Be directly proportional with the RC constant, it is right that the measurement of RC constant is converted into
Figure 681145DEST_PATH_IMAGE006
Measurement.
Described
Figure 580967DEST_PATH_IMAGE006
Measurement module 201 is measured sequential as shown in Figure 2, and RCOUT time measurement module is realized by digital circuit, can carry out the pulse width counting to the RCOUT time constant by the digital dock of using upper frequency, supposes that the digital reference clock is
Figure 84761DEST_PATH_IMAGE037
, count value is N, so
Figure 386429DEST_PATH_IMAGE039
，（5）
Measuring accuracy is by digital dock frequency decision, calculates the RC constant at last to be:
Figure DEST_PATH_IMAGE051
，（6）。
Extend as RC constant measuring method, also comprise the bearing calibration of RC circuit,, in application, generally be converted to correction for the RC constant for the measurement of RC constant, so only need change the control bit of switched capacitor array, but make the RC constant approach the interior value of an error range of receiving.DLC (digital logic circuit) is adopted in the correction of RC constant, RC constant figure adjustment module, as Fig. 3, utilize RCOUT(RC measuring voltage output) pulse width 403, method by digital circuit can easily be proofreaied and correct the RC constant neatly, and whole figure adjustment process was divided into for two steps: initialization 301 and search proofread and correct 302.
During initialization 301, send the RC constant
Figure 684687DEST_PATH_IMAGE006
The correction power on signal (PWR_RCTUNE) 401 of measurement module circuit and reset switch signal (RST) 402.Power on signal 401 should shift to an earlier date some cycles than reset switch signal 402, so that
Figure 71806DEST_PATH_IMAGE006
The measurement module circuit is set up.Promptly begin CNT counter 404 countings after the reset switch signal is sent, the physical circuit work schedule is seen Fig. 4.
Search was proofreaied and correct 302 o'clock, and differential capacitance is made adjustable array format, can get the preset reference count value by formula (6) , realize measuring actual N value and reference by the digital dock of using upper frequency
Figure DEST_PATH_IMAGE052
Value relatively according to comparative result and adjust capacitor array, changes RC value size, and up to making the RC value the biglyyest near default R1*C1 value, correction error is relevant with the capacitor array figure place, and the big more precision of figure place is high more.
In order to accelerate correction rate, reduce calibration cycle, RC constant capacitor array 501 is adjusted and is used binary search algorithm to realize.With 3 capacitor arrays 501 is example, the binary search algorithm state transition diagram as shown in Figure 5, whole searching algorithm can be divided into 3 stages: initialization, search downwards, about search.
During initialization, the extreme higher position 1 of switched capacitor array, other position 0 makes its value of mediating.Pulse width (RCOUT) 403 to the output of differential capacitance circuit is counted.
Search downwards 502 o'clock is judged count value, if less than preset value, shows that then current capacitance is less than normal, this moment current search invariant position (being 1), next searching position 1; Otherwise show that capacitance is bigger than normal, current search position (putting 0).Begin to search for behind next searching position 1 next time, determine until the lowest order direction.
About search 503 o'clock, about capacitor array that downward search procedure is determined, search for, determine setting left and right, counting error minimum in first three state.
Suppose that capacitor array has the N position, then needs this search of N+2 altogether.Each search time is all identical.
In a word; though the present invention has exemplified above-mentioned preferred implementation, should illustrate, though those skilled in the art can carry out various variations and remodeling; unless such variation and remodeling have departed from scope of the present invention, otherwise all should be included in protection scope of the present invention.

Claims (4)

1. the RC constant measuring method of a differential capacitance is characterized in that: comprise differential capacitance circuit module (106) and
Figure 2011100821457100001DEST_PATH_IMAGE001
Measurement module (201);
Described differential capacitance circuit module (106) act as realize RC constant and comparer export the RCOUT time span (
Figure 2011100821457100001DEST_PATH_IMAGE002
) proportionate relationship, the conversion of the concrete duty of circuit and
Figure 105114DEST_PATH_IMAGE002
Be calculated as follows:
1) at t0 constantly, switch S 1(101) closure, reset circuit, at this moment
Figure 959938DEST_PATH_IMAGE003
, RCOUT is output as low, because of
Figure DEST_PATH_IMAGE004
, flowing through resistance R 1(102) and electric current is:
Figure 677358DEST_PATH_IMAGE005
，?（1）
2) at t1 constantly, switch S 1(101) disconnect, reseting procedure finishes, and flows through resistance R 1(102) electric current I passes through C1(103), have:
Figure DEST_PATH_IMAGE006
, release:
Figure 10250DEST_PATH_IMAGE007
Have
Figure DEST_PATH_IMAGE008
, (2)
This moment output voltage Descend, finally cause
Figure DEST_PATH_IMAGE010
, comparer (105) output switching activity, RCOUT transfers high level to by low level, by switch S 1(101) be disconnected to the RCOUT level and uprise this process, the time is:
，（3）
If fixed coefficient is
Figure DEST_PATH_IMAGE012
,
Figure 724238DEST_PATH_IMAGE013
,
Figure DEST_PATH_IMAGE014
,
Figure 860821DEST_PATH_IMAGE015
, then
Figure DEST_PATH_IMAGE016
, (4)
By formula as can be known,
Figure 467383DEST_PATH_IMAGE002
Be directly proportional with the RC constant, it is right that the measurement of RC constant is converted into
Figure 398430DEST_PATH_IMAGE002
Measurement;
Described
Figure 90442DEST_PATH_IMAGE002
Measurement module (201), its RCOUT time measurement module are realized by digital circuit, can carry out the pulse width counting to the RCOUT time constant by the digital dock of using upper frequency, suppose that the digital reference clock is
Figure 827454DEST_PATH_IMAGE017
, count value is N, so
Figure DEST_PATH_IMAGE018
，（5）
Measuring accuracy is by digital dock frequency decision, calculates the RC constant at last to be:
Figure 288523DEST_PATH_IMAGE019
，（6）。
2. according to the RC constant measuring method of the described a kind of differential capacitance of claim 1, it is characterized in that also comprise the correction of RC circuit, trimming process was divided into for two steps: (302) are proofreaied and correct in initialization (301) and search;
During initialization (301), send the RC constant
Figure 656050DEST_PATH_IMAGE021
The correction power on signal (PWR_RCTUNE) of metering circuit and reset switch signal (RST), power on signal (401) shifts to an earlier date some cycles than reset switch signal (402), promptly begins CNT counter (404) counting after the reset switch signal is sent;
When (302) are proofreaied and correct in search, can get the preset reference count value by formula (6)
Figure 897676DEST_PATH_IMAGE023
, realize measuring actual N value and reference by the digital dock of using upper frequency
Figure 107553DEST_PATH_IMAGE025
Value relatively according to comparative result and adjust capacitor array, changes RC value size, up to making the RC value the biglyyest near default R1*C1 value.
3. according to the RC constant measuring method of the described a kind of differential capacitance of claim 2, it is characterized in that: described differential capacitance is made adjustable array format, and binary search algorithm is used in the capacitor array adjustment.
4. according to the RC constant measuring method of the described a kind of differential capacitance of claim 3, it is characterized in that: 3. described binary search algorithm is divided into 3 stages: initialization, search downwards, about search;
1) during initialization, the extreme higher position 1 of switched capacitor array, other position 0 makes its value of mediating, and the pulse width (RCOUT) (403) of RC differential capacitance circuit (106) output is counted;
2) during search (502) downwards, count value is judged,, is shown that then current capacitance is less than normal if less than preset value, this moment current search invariant position (being 1), next searching position 1; Otherwise show that capacitance is bigger than normal, current search position 0 begin to search for behind next searching position 1 next time, is determined until the lowest order direction;
When searching for (503) 3), search for about the capacitor array of after search is finished downwards, determining, determine setting left and right, counting error minimum in first three state;
Suppose that capacitor array has the N position, then need N+2 search altogether, each search time is all identical.
CN2011100821457A 2011-04-01 2011-04-01 RC constant measuring method of differential capacitance Pending CN102226822A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114337600A (en) * 2022-03-11 2022-04-12 华南理工大学 On-chip differential active RC filter calibration and tuning method

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20050140431A1 (en) * 2003-12-30 2005-06-30 Riches James J. Offset, delay and parasitically immune resister-capacitor (rc) tracking loop and method of using same
CN101222206A (en) * 2007-01-09 2008-07-16 宽达科技股份有限公司 Method and device for correcting time constant of chip built-in resistor and capacitor
EP1962421A1 (en) * 2007-02-23 2008-08-27 STMicroelectronics S.r.l. Calibration circuit for calibrating an adjustable capacitance of an integrated circuit having a time constant depending on said capacitance
CN101820261A (en) * 2010-04-21 2010-09-01 广州市广晟微电子有限公司 Device and method for correcting cut-off frequency of filter
CN102226823A (en) * 2011-04-01 2011-10-26 广州润芯信息技术有限公司 Measuring method of RC constant of ground capacitance

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20050140431A1 (en) * 2003-12-30 2005-06-30 Riches James J. Offset, delay and parasitically immune resister-capacitor (rc) tracking loop and method of using same
CN101222206A (en) * 2007-01-09 2008-07-16 宽达科技股份有限公司 Method and device for correcting time constant of chip built-in resistor and capacitor
EP1962421A1 (en) * 2007-02-23 2008-08-27 STMicroelectronics S.r.l. Calibration circuit for calibrating an adjustable capacitance of an integrated circuit having a time constant depending on said capacitance
CN101820261A (en) * 2010-04-21 2010-09-01 广州市广晟微电子有限公司 Device and method for correcting cut-off frequency of filter
CN102226823A (en) * 2011-04-01 2011-10-26 广州润芯信息技术有限公司 Measuring method of RC constant of ground capacitance

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114337600A (en) * 2022-03-11 2022-04-12 华南理工大学 On-chip differential active RC filter calibration and tuning method
CN114337600B (en) * 2022-03-11 2022-06-03 华南理工大学 On-chip differential active RC filter calibration and tuning method

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Application publication date: 20111026