EP1264190A1

EP1264190A1 - Circuit and method for evaluating capacitors in matrices

Info

Publication number: EP1264190A1
Application number: EP01913677A
Authority: EP
Inventors: Ute Kollmer; Stephan Sauter; Carsten Linnenbank; Roland Thewes
Original assignee: Infineon Technologies AG
Current assignee: Infineon Technologies AG
Priority date: 2000-03-06
Filing date: 2001-02-16
Publication date: 2002-12-11
Also published as: WO2001067119A1; KR20030009381A; US20030062905A1; US6870373B2; DE10010888B4; DE10010888A1

Abstract

The invention relates to a circuit for evaluating the capacitors of a matrix which has a plurality of rows (12, 13) with at least one capacitor (Cchar) in at least one dimension, comprising a testing branch (2) which is connected to first electrodes of each of the capacitors (Cchar) to be evaluated and with which two different potentials (V1, V2) can be applied to the first electrodes; and a measuring branch (3) which is connected to second electrodes of each of the capacitors (Cchar) and which has a first measuring path and a second measuring path. A common potential (V0) is applied to said first measuring path and second measuring path, the first measuring path having an instrument (1) for evaluating the capacitors (Cchar). The first measuring path and the second measuring path can be connected to the second electrodes. The circuit is characterised by control means which can individually switch each of the capacitors (Cchar) to be evaluated to the two different potentials.

Description

description

_S chaltungsanordnung and method for evaluating capacity in matrices

The present invention relates generally to a circuit arrangement and a method for evaluating capacitances in m arrays.

The most exact possible assessment of capacities, that is to say the numerical determination of a value of the capacitance m of an intended unit, plays an important role in numerous / applications of technology, particularly in the case of small capacities. For certain measuring purposes, for example, where the size of the capacitance must be known as precisely as possible, a precise determination of the capacitance (s) occurring in the circuit is essential for obtaining the desired result.

Especially for the parametric description of CMOS

Processes and other technologies require the / absolute value of intended on-chip capacities, for example for analog applications, and unintended but technically unavoidable parasitic capacities, e.g. B. to characterize line coverings, line crossings in different metal levels, etc. For the sometimes very critical analog applications, it is also necessary to know the matchmg behavior (pairing behavior) of desired on-chip capacitances, i. H. capacity ratios must be characterized.

In order to be able to evaluate a large number of design variants with a low chip area consumption and / or - also with an acceptable chip area consumption - a good static basis for the investigations carried out, e.g. B. for mat chmg studies, it is useful to arrange the capacities to be characterized in m matrices.

In addition, matrix-shaped capacitance arrangements z. B. be carried out in capacitive sensors, the task of which is to measure capacitively detectable parameters within certain limits as a function of the location (examples: spatially resolved pressure sensors, fingertip sensor).

Very high accuracy is desirable or required for this case in certain applications. Some measuring methods or circuits are known in the prior art which convert the capacitance to be characterized into a current, a voltage or a frequency, since these parameters can be measured relatively easily with high accuracy using external measuring devices. A direct measurement of the capacitance value is anyway not possible due to the parasites m external feed lines, feed lines and pads on-chip.

Circuits for on-chip capacitance-voltage, on-chip capacitance-current, or on-chip capacitance-frequency conversion are also required in products with which sensor signals, which come from capacitive sensors, are evaluated and have to be further processed (e.g. capacitive pressure sensors, defogging sensors, ...)

All previously known circuits, however, have the disadvantage that internal parasitic capacitances and other non-idealities of the components used lead to a certain measurement error, which is greater the smaller the capacitance to be characterized. The prior art specifies principles and circuits which convert the value of capacitances or the ratio of two or more capacitances into a quantity which is easier to handle, such as current, voltage or frequency or current, voltage or frequency ratios. However, all of these circuits have the disadvantages listed below:

• Parasitic capacitances and other non-ideal properties of the real components used in the respective evaluation circuit falsify the measurement result or have to be compensated as far as possible with circuitry means. However, none of the previously known compensation methods leads to complete error suppression.

• Many of the specified concepts normalize the measured values to an integrated, but not exactly known quantitative reference capacity. Thus, although these methods allow statements about capacity ratios, as are required for Matchmg examinations, precise circuits are, on the one hand, very complex and the resolution achieved remains limited by parasitic effects and non-idealities of the components used, despite all design effort. Absolute value determinations of small capacitances (e.g. line crossings), which are essential for process parameterization, are impossible with such circuits anyway.

For example, Chen et al. In the "Proceedings of the IEEE International Conference on Microelectronic Test Structures", 1997, page 77 and "IEEE Transactions on Semiconductor Manufacturing", Volume 11, No. 2, 1998, page 204, an evaluation circuit was proposed. However, even with this method it was not possible to use real components completely exclude emerging parasitic capacities from the measurement.

In summary it can be said that today Thode no metal or circuit is known, the zise a simple and pre ^¬, Para Sitar effects and the influence of non-ideal properties of the evaluation circuit components used free determination of the absolute values of capacities, especially of On-chip capacitances m matrix arrangements of capacitances allowed. The same applies to circuits for the precise evaluation of capacitance ratios. Of course, if a high-precision circuit or method for determining the absolute value is available, the problem of characterizing capacitance ratios is solved at the same time.

The invention is therefore based on the object of providing a circuit and a method which can be used with this circuit and which enables the measurement-related elimination of parasitic effects and other deviations in the correct determination of capacitances in matrices.

This object is achieved by the circuit arrangement for evaluating capacities in matrices according to independent patent claim 1 and the method for evaluating capacities in

Matrices solved according to independent claim 21. Further advantageous aspects, details and refinements of the present invention result from the dependent patent claims, the description and the attached drawings.

The invention is initially directed to a circuit arrangement for evaluating the capacities of a matrix, which in at least one dimension has a plurality of rows with at least one capacitance, with a test branch which is connected to a first electrode of each of the capacitances to be evaluated and with which two different potentials can be applied to the first electrodes, a measuring branch which is connected to the second electrodes of each of the capacitances to be evaluated and which has:

a first measuring path and a second measuring path which are present at a common potential, the first measuring path having an instrument for evaluating the capacitance and the first measuring path and second measuring path being connectable to the second electrodes; wherein the circuit arrangement is characterized by control means which can switch each of the capacitances to be evaluated individually to the two different potentials.

The capacitances to be evaluated are to be understood here as all the capacitances occurring in a matrix that have to be measured, for example on-chip capacitances that can be produced with semiconductor processes or capacitances with discrete circuit arrangements, capacitors etc.

A matrix has an arrangement of capacities. In the simplest case, this is a single set of capacities. Such a matrix could be described as one-dimensional, since there is an arrangement of capacities in only one of the dimensions. A two-dimensional matrix has a plurality of rows of capacities (in contrast, the one-dimensional matrix has only one capacitance for each of these rows), each of the capacities in one row belonging to a different row of capacities in the other dimension. Accordingly, each of the capacities is defined by its clear assignment to the rows of the two dimensions. The same applies to three- or multi-dimensional matrices, but with more groups of rows of capacities. Each capacitor has two electrodes that are connected to the rest of one Circuit are connected. In the case of the circuit arrangement for the evaluation of capacity, the part of circuit, to which the verbun one electrode of each of the capacitances ^¬ is referred to as the test arm as it is involved in examining the capacity and connected with said other electrode of each of the capacitances branch is called the measuring path, which is so called because it contains the actual Mes ^¬ solution, ie assessment of capacity to be. A path is to be understood here as an electrical control system which uniquely connects points and into which, in addition to the actual conductors, further elements such as switches, transistors and measuring instruments can be incorporated.

This circuit arrangement according to the invention enables the method according to the invention for evaluating capacitances to be carried out due to the fact that the various potentials can be applied.

The basic principle of the invention consists in activating at least one of the capacities to be assessed, i.e. to apply the potentials to them in order to be able to carry out an evaluation of the capacitance and then to carry out a measurement-free evaluation of the capacitance by means of the measuring branch. Capacities can also be grouped with suitable control, so that several capacities can be evaluated at the same time. It is also possible to assign a plurality of evaluation circuits to a corresponding matrix of capacities, which are either responsible for sub-areas of the matrix or which can all be connected to any capacities of the matrix.

Preferably, the drive means for each dimension of the matrix of an arrangement of switching paths, wherein _E ach of the rows with capacities is a circuit path is at least sen zugewie- having a control and zuminαest a switchable by the drive, m the Prufzweig integrated control switching element at least one of the two different which potentials to the first electrodes in a row

Makes capacities investable.

_In this way, an n-dimensional grid of switching paths is formed, with which, by selecting one of the rows per dimension, a specific capacitance located at the intersection of the rows can be controlled. The activation is done simply in that the first and second Po be ^¬ tential connected to the electrode of the capacitor, what happens to the switching elements, which the respective capacitance your health for each of the dimensions of a spot of fr portion of Prufpfads m the Prufpfad incorporated become .

There is the possibility that the switching paths of at least one dimension for each of the capacitances of a row have at least one control switching element integrated into the part of the test branch leading to the capacitance. For such dimensions, each part of the test branch that supplies a capacitance has its own control switching element for its activation. The control switching elements of a number of capacitances, which are controlled by a switching path, are switched simultaneously.

Alternatively, the switching paths of at least one dimension for each of the rows of capacitors can have at least one control switching element integrated into the part of the test branch leading to the row. In this variant, therefore, not every capacitance m of the respective dimension can be switched individually, but only entire rows can be switched. This represents a simplification compared to the above possibility, since only one control switching element is required for each of the switching paths. It goes without saying that the two con- Scepter of the connection can be combined with each other, so that for example for a first dimension ede individual

Capacity receives its own switching element and for a second dimension all capacities are activated via a common control switch.

To implement the control of the switching paths, the control means can have an address decoder with an individually controllable output for each of the rows of capacitances, and the controls can have a signal line between each output and the control switching element. A separate address coder is required for each of the dimensions, whereby the address decoders of the individual dimensions can be combined to form a common unit.

In a simple preferred embodiment, an alternating voltage can simply be applied to the test branch, the amplitude maxima of which then each represent the two different potentials. The AC voltage can preferably be a square-wave voltage in order to make a clear and quick back and forth

To enable switching between the two different potentials.

Alternatively, it is also possible for the test branch to have a first test path with a first switching element and a second test path with a second switching element for each of the capacitors, a first potential being present on the first test path and a second potential on the second test path, and both test paths via one Nodes are connected to the first electrode. This preferred arrangement ensures, by means of the two switching elements, that the different potentials can be applied to the electrode of a capacitor. In this case, connectivity is via switching elements, which are integrated into the test paths. _V orteilhafterweise both Prufpfade should be switched on at a time. Therefore, it is preferred that the switching paths to ^¬ least one dimension for Ede the capacities of a number m a first Prufpfad integrated control switching element and a second m Prufpfad integrated control switching element having.

This circuit arrangement can also be simplified, as above, in that the switching paths of at least one dimension for each series of capacitors have a control switching element integrated in the first test path and a control switching element integrated in the second test path. In this embodiment, all capacities in a row that are controlled by a common switching path are in turn switched by a single control switching element (provided the corresponding control switching elements are also switched on in the other dimensions).

The above with regard to the switching elements also applies in the measuring branch, which can be characterized in that the

The first measuring path is connected via a third switching element and the second measuring path is connected via a fourth switching element. At least one of the switching elements is preferably a transistor. In fact, in conventional circuits, especially in semiconductor circuits, all of the switching elements will be transistors.

The instrument for evaluating the capacities is preferably an ammeter. However, it is also conceivable to use other instruments if they are suitable for carrying out an assessment of the capacities to be assessed. In particular, so-called integrating measuring devices are used which are able to establish a current flow integral on the measuring path _b . As will be explained in detail below, an evaluation of the capacitance by means of the MESSIN ^¬ struments during charging or during discharging of the capacity with the potentials. On the other hand, no evaluation is carried out on this measuring instrument during the complementary process, i.e. unloading or loading.

However, it is possible to integrate a second measuring instrument into the second measuring path, which carries out a second evaluation of the capacity, which is independent of the first evaluation, during the process which is complementary to the first evaluation, that is to say unloading or charging. The accuracy of the method according to the invention can be further increased by comparing the two independent evaluations thus obtained.

An important aspect in the method according to the invention is the time-coordinated application of the different potentials to the different paths or branches of a circuit arrangement. Therefore, clock signals are preferably provided to control the switching elements, which are fed directly or indirectly to the switching elements and which can make it possible to periodically and synchronously apply the various relevant potentials to the electrodes of the capacitance to be evaluated. These different clock signals can be generated independently of one another or have a common origin. For example, it is possible that a common alternating clock voltage is present as a clock signal on the first switching element and on the second switching element and the first or second switching element are designed such that they can be switched or switched alternately by the alternating voltage. For this purpose, for example when using transistors, it is advisable that the first and second _S chaltelement having a pMOS and an nMOS transistor which are alternately tet geschal ^¬ from the clock or AC voltage can be switched.

In order to ensure the synchronization of the clock signals or a possibly used alternating clock voltage in a simple manner, it can also be preferred that the circuit arrangement further comprises: a means for generating the clock signals applied to the switching elements and, if appropriate, a used alternating clock voltage from a master clock signal.

Thus, only one master clock signal is required in order to generate therefrom all other clock signals necessary for executing the method according to the invention with the circuit arrangement.

In order to further simplify the design of the circuit arrangement, it may further be preferred that the common potential is equal to the first or the second potential.

Again, it can be advantageous if the first or second potential represents an operating voltage that is inherent in the circuit arrangement anyway, and the other of the second or first potential is the ground.

The invention is further directed to a method for evaluating capacities, in particular using the circuit arrangement according to the invention described above, with the following steps:

Activation of at least one specific capacity to be evaluated of a matrix which has a plurality of rows with at least one capacity in at least one dimension, Charging and discharging the activated capacitance to be evaluated by alternately applying a first and a second potential which is different from the first to a first electrode of the capacitance via a test branch and

Applying a common potential to a second one

Electrode of the capacitance via a measuring branch; and

At least evaluating the capacity during the loading or unloading of the capacity in the measuring branch.

With regard to the advantages and details of the method according to the invention, reference is made to what has been said above regarding the circuit arrangement and full reference is made to it. It also goes without saying that everything that has been carried out for the method according to the invention should apply in the same way to the circuit arrangement according to the invention. The principle of the method according to the invention is based on the fact that after activation of a specific capacitance in a matrix of capacitances, one of the two electrodes of the capacitance to be evaluated (when using a switching arrangement according to the invention, the electrode connected to the test branch) is periodically recharged between two potentials. while the other electrode remains at a common potential and the capacity is only assessed on the basis of the charging or discharging process.

The activation is preferably carried out by switching on the part of the test branch leading to a specific capacity.

The switching on of the specific part of the test branch can take place by means of control switching elements integrated in this part of the test branch, a control switching element being provided for each of the dimensions.

Alternatively, the switching on of the specific part of the test branch can be carried out by control switches integrated in the test branch. sliding elements take place, wherein for at least one of the dimensions of a control switching element in that particular part of the Prüfzweigs is integrated, and for at least one of Dimension ^¬ versions a control switching element in a portion of the Prüfzweigs is integrated, which leads to a number of capacities and which also includes certain Part heard. These two embodiments can be combined with one another in several dimensions.

The at least one evaluation of the capacitance is preferably carried out by an instrument which is integrated in a first measuring path of the measuring branch. This measuring instrument can be, for example, a current measuring device, so that the evaluation can be carried out by measuring a current flow integral through the first measuring path of the measuring branch during the charging or discharging of the capacitance.

In order to minimize the error during the measurement evaluation of the capacity, it is particularly preferred that in the case of the evaluation of the capacity during charging the at least one evaluation does not take place during the unloading, and that in the case of the evaluation of the capacity during the unloading the at least one evaluation was not made during loading.

The common potential applied according to the invention, which must be carried over the measuring instrument during the evaluation, is preferably applied directly to the second electrode via a second measuring path of the measuring branch, while the at least one evaluation is not carried out. In this way it is possible to reliably ensure that a measurement is carried out via the measuring instrument only during the actual measuring process, that is to say either during charging or during unloading, and nevertheless the second electrode remains at the common potential throughout the entire time for a recharging to ensure. The time profiles of the measurement during loading and unloading described above do not mean that at all times a measurement must be performed or must be applied to a ^¬ be-determined potential to the electrodes. Rather, it is also possible to apply potentials or to carry out measurements only over certain time intervals, while in other time intervals the arrangement used for the method according to the invention is completely decoupled from all external potentials and is therefore also not measured.

However, it is preferred that the capacity rating be done so that the entire charging or discharging process is detected.

As already explained above with regard to the device, a further, independent evaluation can take place during the complementary process to the at least one evaluation. The invention therefore preferably has the further step: second evaluation of the capacity during the process of unloading or charging, in which the at least one evaluation is not carried out.

The second evaluation of the capacitance is preferably carried out by a second instrument, which is integrated in a second measuring path, in order to ensure that the current flow derived from the first instrument during the complementary one

Operation of unloading or loading can flow through the second instrument.

The alternating application of the first and second potential to the first electrode can, for example, be carried out in a simple manner

Case by applying an AC voltage to the test branch. However, it is also possible that the alternating application of the first and the second potential can take place by alternately connecting a first test path with a first potential and a second test path with a second potential to the first electrode. This connection can take place, for example, by means of switching elements integrated in the test paths, for example switches or transistors.

In order to ensure that the capacitance is actually only evaluated during the desired process, for example charging or discharging, it is possible for the first measuring path and the second measuring path to be connected alternately to the second electrode. This connection can also be carried out by means of switching elements integrated in the measuring paths.

A particularly preferred embodiment of the method according to the invention leads to a further reduction in the measurement error, since the mismatch within the measurement branch is eliminated. This procedure has the following steps:

Interchanging the temporal correlation between the application of the first and second potentials and the at least one evaluation during charging or discharging;

-Reassess the capacitance in the measuring branch; and

-Determine the capacity more precisely from the two evaluations.

The temporal correlation can be interchanged, for example, by shifting the phase of the AC voltage by 180 ° with respect to the period of the at least one evaluation, or by either interchanging the timing of the two measurement paths or applying the two potentials to the test branch ,

In the following, the invention is to be explained on the basis of preferred exemplary embodiments, reference being made to the attached Reference will be made to drawings in which:

1 shows a circuit arrangement which can carry out the actual evaluation of each individual capacitance;

2 shows an exemplary embodiment of a circuit arrangement according to the present invention;

3 shows a further exemplary embodiment of a simplified circuit arrangement according to the present invention;

FIG. 4 shows yet another exemplary embodiment of a circuit arrangement according to the present invention using AC voltage.

Before the invention is explained in detail, the circuit arrangement used for the evaluation of an individual capacitance is to be presented first. FIG. 1 shows a schematic illustration of a basic circuit which can be used in the invention. The capacitances C _p , ι ₂ and Cp, ₃₄ shown in the figure represent the parasitic capacitances at the nodes Nι ₂ and N _{34 which} are unavoidable in real technical applications. Their effect on the function of the circuit, or the fact that these parasitic capacitances do not falsify the measurement result, is discussed in detail below.

The principle shown in FIG. 1 is based on the fact that a first electrode of capacitance C _ch ar. which is connected to the node N _{12 of} the test branch 2, is periodically reloaded between the voltage values V _x and V ₂ which are present on the two test paths, while the other, second electrode which is connected to the node N ₃ -, the measuring branch 3 is connected to the common potential V remains ₀ and the average value of the currency only ^¬ end of the charging (or depending on the definition and choice of Vi, V ₂ and V ₃₄ optionally also of Discharge) process occurring displacement current is measured, which occurs between the electrode of the capacitance, which is at constant potential V ₀ , and the voltage source, which supplies this potential. This happens because

• That one of the two electrodes of the capacitance (the one that is connected in the figure to the node N _{i2 of} the test branch) by means of the switching elements (here the transistors T1 and T2) in a periodic change according to the timing diagram shown in the figure is connected to the potentials Vi and V ₂ , so that the node N _{i2 is} reloaded with the same period between these two potentials,

• that the other of the two electrodes (the one that is connected in the figure to node N _{34 of} the measuring branch) is connected to a fixed potential, for example V ₀ , the connection of this electrode to the voltage source having the potential V ₀ delivers, according to the timing diagram shown in FIG. 1a, either via the current test path that is created by closing transistor T3 or via the current test path that is created by closing transistor T4,

• and that either the displacement current occurring with the charging or with the discharge process (in the figure la ϊmeas, ₃ ) is measured by means of a suitable instrument which is sluggish with respect to the selected clock frequency and thus has an integrating effect, and this current measuring instrument 1 either (as shown in the figure) in the same current measuring path as the transistor T3 or in the same current measurement path as the transistor T4.

Here, other forms of switching elements can be used at all points instead of the transistors shown.

As can be seen from the timing diagram in FIG. 1 a, all the signals Φi, Φ ₂ , Φ ₃ , and Φ ₄ used for the control have the same frequency, but different phase positions and possibly also different duty cycle relationships.

According to the timing diagram shown in FIG. _{1 a} for the “OPEN” and “CLOSED” state of the transistors T _x , T ₂ , T ₃ , and T _4, which is determined by the control signals Φ _lt Φ ₂ , Φ ₃ , and Φ ₄ is defined, compliance with the following two conditions that are advantageous for the functioning of the method is guaranteed:

• The node N ₃₄ is connected to the potential V ₀ via exactly one of the two possible measurement paths before the start and after completion of a recharging process of the capacitance to be evaluated, so that the current measuring instrument 1 - depending on whether it is m on the same measurement path as the transistor T ₃ or m lies in the same measuring path as the transistor T _A - either measures the displacement current, which corresponds to the entire charging process, or measures the displacement current, which corresponds to the total discharge process of the capacitance C _Char .

• Frequency and duration of the "OPEN" phases of the signals Φ _lr Φ ₂ , Φ ₃ , and Φ ₄ are chosen so that the potential at node Nι ₂ during the reloading process safely reaches the full values V _x and V ₂ . Tent intervals are also shown in the timing diagram of Figure la (dotted areas) in which one or the other or both of the two electrodes of the capaci ty ^¬ C _{C ar} "float". In particular, an exactly complementary control of the transistors T ₂ and T _{2 is also} possible, ie that the closing of Ti (T ₂ ) takes place simultaneously with the opening of T ₂ (Ti) or that the control signal Φ_ is exactly complementary to Control signal Φi is.

The capacitance is calculated from the parameters Ni, V ₂ and f = 1 / T using equation (1) given above. The choice of the potential V ₀ has no influence on the measurement result, provided that C _C har is independent of the voltage, ie it is an ideal capacitance.

The measurement result is also not of the value and of the other properties such. B. linearity or voltage dependency, which influences parasitic capacitances C _p , _{^ 2} and C _p , ₃₄ . The parasitic capacitance C _p , ι _{2 is} also recharged between the potentials V _x and V ₂ , but the current required for this flows exclusively through the transistors Ti and T ₂ and through the sources Vi and V, but not via the transistors T. ₃ and Ti, and therefore not via the current measuring instrument 1 and the source V ₀ . As the measured variable r _{meaS / J} , the displacement current flowing between node Ν ₃₄ and voltage source V ₀ is used here, and this is exactly the same as the current required for recharging the electrode of C _ch ar connected to node N ^ (≠ total current for reloading the node Ni, this measurand is not affected by the parasitic capacity C _p , ι ₂ . The parasitic capacitance C _p , ₃₄ is also not included in the measurement result, since, as a result of the constant potential at node N _4, it is not recharged during the entire measurement process and thus does not lead to the occurrence of a charge / discharge current which can be assigned to this capacity.

It is possible to interchange the clocks Φi and Φ ₂ or Φ ₁₂ (if the connection is made via n-MOS and p-MOS transistors Ti or T ₂ ) or to invert the clocks Φ _^ and Φ ₄ , or to measure the current not in the path with the transistor T ₃ but in that with the transistor T ₄ . In the case of ideal components and measuring instruments, all of these measures affect only the sign of the mean value of the measured variable F _meas , but not the amount thereof.

The average over time of the measured current results for this ideal arrangement according to

Ϊmeas 1 = Cchar X (V _x - V ₂ ) X f (1)

where f = 1 / T and T is the period. This results in the capacity to be assessed

Char, with f = 1 / T = clock frequency (2a)

'- | r + mT "\ /

J β _as i (t) d / (fx -M - Vj)), x any, m = 1, 2, 3, (2b)

[ml _τ J ^f - 1 | r ^r + ⁺ m ^m T ^T ^ /

- | lmβasi (dt / (V ₁ -V ₂ ), τ any, m = 1, 2, 3, (2c) mr) l easi stands for the time average of the measured current I _me as, ι (t) an entire period T or an integer multiple thereof, the starting point x of this period (s) being arbitrary. In measurement technology practice, the value of C _ch ar is obtained. by looking at the mean of the charging current I _meas , ι at a frequency f that is not too low

(e.g. f> 10 kHz) with the aid of a measuring instrument which is to be worn at the selected frequency in order to follow the time course of the current, e.g. B. all types of the parameter analyzers offered by Hewlett-Packard, via one

Measures the length of time, which is large compared to the period T.

In this case, the measuring instrument has an integrating effect.

Furthermore, parameter variations of the transistors T play _. and T ₂ doesn't matter. Mismatch of the transistors T ₃ and T ₄ can, however, lead to a slight falsification of the measurement result, but this can be completely compensated for by repeated measurement of a branch current with an inverted signal Signal _i2 (referring to FIG. 1 b)). The capacity is calculated in this case

Cchar = (I r _mess , ₃ (Φ12 not inverted) | + | ϊ ^" _mess , ₃ (Φ ₁₂ inverted) I) / [2 x (V _: - V ₂ ) xf] (2a)

respectively.

Ccnar = (I ϊ mess,. (Φ ^* i2 not inverted) | + I ϊ ^" _meΞΞ , ₄ (Φ ₁₂ mverted) I) / [2 x (V _: - V,) xf] (2a)

Similarly, a mismatch in the levels of the signals Φ ₃ and Φ can have a similar effect to a threshold voltage mismatch of the transistors T ₃ and T ₄ . This effect is also compensated for by the above-mentioned measure or can be prevented from the outset in that the signals provided for controlling the gates of T ₃ and T ₄ are buffered on-chip by inverters, which in turn are operated with identical supply voltages. Gem _ä ß the timing diagram m Figure la, it is possible Φ = Φ _^ choose to w _ä. Lb shows this very gunsti ^¬ for practice ge special case is shown. The signals .phi..sub.i and Φ ₂ of Figure la are here combined to form a signal Φ _i2, the ert the common gate terminal of the transistors Ti and T ₂ ansteu ^¬. The transistors Ti and T ₂ this case form a simple CMOS inverter only for the control an input signal is required, which represents an advantageous simplification compared to the circuit from FIG.

The frequency and duration of the corresponding time intervals of the clock signals Φi, Φ ₂ . Φ ₃ and Φ ₄ , or Φ _i2 , Φ ₃ , and Φ ₄ must be chosen in this concrete implementation, which is carried out with real components, so that a charge of the capacitance C _C nar to the full value of Vi or a discharge the full value of V _{2 is} possible and that the respective displacement currents completely subside during the time intervals that T ₃ or T ₄ conducts.

Figure 2 shows an embodiment of the invention

Circuit arrangement with an N x M matrix circuit based on a CMOS process, in which the principle according to FIG. 1 was applied to a matrix arrangement. There are rows of capacities in one dimension (12) and in the other dimension (13). Each "cell" within this matrix 5 containing in addition to being valued capacitance C _C ha, ^, y, x = 1, 2, 3, ..., y = 1, 2, 3, ... transistors _Tx, ^ and T_, _{> / V} , whose function corresponds to the function of transistors Ti and T_ in FIG. 1, furthermore transistors T <=,, _y , T ₆ ,,, _y , Tι ,,, _y , and T ₈ ,>, _y as control switching elements, by means of which the

Exactly one capacity or cell is selected within the matrix. The transistors T ₅ , _y , _y , T _{6r /} , _y , T _{7, y, y} , and T _e ,, _y which addressed via switching paths 6, 7, 8, 9. The

Function of the transistors T ₉ , _Xfy and Tι ₀ , _x , _y is discussed below.

The selection is made by two control means, the x and y decoders 10, 11, on exactly one of their outputs X _O UT _x , x = 1 ... N, or YOUTy, y = 1 ... M, respectively supply a logic H signal (H) and a logic L signal (L) to the switching paths 6, 8 at all other outputs. The corresponding logical complementary signals are present at the complementary outputs XOUT _x and YOUT _y for the switching paths 7, 9.

As a result, the transistors T ₅ , _x , _y , T ₆ are exactly in the cell 5 with the coordinates x and y with 1 <x <N and 1 <y <M, for which XOUT _x = H and YOUT _y = H apply , _x , _y , T ₇ , _x , _y , and T _{8 / X} , _y in the conductive state, so that a recharging of the capacitance located in this cell via the transistors Tι, _x , _y and T ₂ controlled by the signal Φ _i2 , _x , _{y is} possible. The transistors Tq,, _y , and Tιc _rX , y in this cell are also both in the blocked state, so that they do not influence the recharging process. In all other (not selected * cells ") at least one of the transistors T ₅ , _x , _y and T ₆ , _x , _y , and at least one of the transistors T ^, _} , _y and T ₈ , _x , _y blocks, so that it is not possible to charge the capacitors within these cells via the transistors Tι _rX , _y and T _z , _x , _y , _and there is at least one of the transistors T ₉ , _x , _y and Tιo, _> , _y within these cells in the conductive state, so that a defined potential (here V - V ₀ ) lies over all capacities which are not selected. Table 1 shows the result of a simulation of a 2 x 2 matrix which contains capacitances whose values scatter around the mean 10 fF V _: = VDD = 3.3 V, v ₂ = V ₀ = GND potential

= 0 V, and T = 1000 ns selected.

The technology parameters for the transistors Ti - T ₄ originate from a 3.3 V CMOS process with an oxide thickness of 9 nm and a minimum channel length of 0.5 µm. The channel length of all transistors was chosen to be L = 1 µm. W = 10 μm applies to the width of the transistors T ₃ and T ₄ , all other n-MOS transistors have the width W = 1 μm, and all p-MOS transistors have the width W = 2 μm.

Table 1: Simulation of 2 x 2 matrix according to Figure 2. V ₂ = VDD = 3.3 V, V ₂ = V ₀ = GND potential = 0 V, and T = 1000 ns.

As can be seen, an excellent agreement between the results here in the simulation for C _ch a _r, _x, _y specified values and the determined value. The amount of the absolute evaluation error is below 0.002 fF, the amount of the relative measurement error is therefore <0.02%. With the operating voltage of VDD = 3.3 V used in the simulation, this corresponds to an error of approximately 40 elementary charges q (q = 1.602 10 ^"1Q As). It can therefore be assumed that this Deviations are due to numerical inaccuracies of the simulator and not due to the properties of the circuit.

The following comments should supplement the explanation of this embodiment:

• If it is permissible that an electrode of the non-selected capacity ^¬ "floated" to the transistors T _9, _x, _y and Tιo, _x, _y omitted.

• The order of the transistors T _{l X} , _y , T ₅ , _x , _y and T ₆ _,, _y and _Λ , _y T ₇ , _x , _y and T ₈ , _x , _y can be interchanged. Furthermore, it is possible to execute the selection transistors with respect to one coordinate, ie either T ₅ , _x , _y and T ₈ , _x , _y or T ₆ , _x , _y and T, _x , _y not individually within each cell, but for the whole Columns (first dimension) or for entire rows (second dimension).

FIG. 3 shows a further embodiment of the present invention, in which, according to the comments made above, a possible reversal of the order of the transistors within a cell was carried out, the transistors for x selection T ₅ ,, _y and T ₈ ,., _Y from FIG 2 were replaced by transistors T _3, and T ₈ , _x , which now select complete rows 12 of one dimension, and m the transistors T _9, ,, _y and Tιo, _x , _{y have been} omitted. Furthermore, _Vl = VDD = 3.3 V and V ₂ = V ₀ = GND potential = 0 V were chosen.

FIG. 4 shows a further simplified embodiment of the present invention, in which the test branch 2 is fed by an AC voltage 4. Here, it is easy for _E ach cell 5 for each dimension, a control switching element depending _SWι, _{provided y} (for the Y-decoder 11) and SW _X, _y (for the X-decoder 10), which m the _har to the capacitance C _{, y} , _y leading test branch is integrated. Instead of the individual control sliding elements, transistors here, it is also possible to transfer gates ^¬ (n parallel p) to use in each of which an n-MOS and p-MOS transistor ensure that the full voltage can be constructed. In accordance with the transistor technology used, the converted outputs to X _out and Y _out are also required for control.

As previously discussed, mismatch of transistors T ₃ and T ₄ can lead to a certain falsification of the measurement result. Parameter variations of all other transistors used in Figures 2 and 3 are not critical. Furthermore, a mismatch with the levels of the signals Φ ₃ and Φ ₄ can also be understood here as a threshold voltage mismatch of the transistors T ₃ and T ₄ , which then also manifests itself as a small measurement error.

As with the simple circuit according to FIG. 1, such errors can be measured twice by measuring a branch current with a non-inverted and inverted signal 2ι ₂ and calculating the capacitance according to Eq. (2) can be fully compensated. Furthermore, the gate signals of T _Δ and T _{4 can} also be buffered here with inverters which lead to completely identical levels for both transistors.

In the event that capacity ratios (e.g. for investigations into capacity matching) are to be assessed, such compensation measures can often also be omitted for highly precise requirements, as will be shown in the following discussion.

In the following, the case is to be examined in which two capacitors with the aid of one of the circuits according to the invention the values C _cha r, ι = C _{c a.} ⁺ ^ δCchar and Cchar 2 = C ^. - 1 δC _C har ms

Ratio C _char , _ι / C _char , ₂ should be set.

The real relative deviation of the capacitance values δr is then:

δr: 3)

When calculating the measurement error for the capacitance ratio, it must be taken into account that the measurement error ΔC _char caused by parameter variations of T ₃ and T ₄ has the same effect on C _cha r, ι and C _cha r, 2, since the transistor pair T ₃ and T _{4 is} only present once in the entire matrix and is used for the evaluation of all capacities. For the deviation Δδr we get the difference between the measured and actual value for δr:

Δδr

= ö - ^* char

(4b)

Cchar ^{+ Δ <} ^ c ar

Under the (applicable) condition that the measurement error ΔC _char / C _{char is} small against 1, Eq. (4) can also be written approximately as Δδr = from which Δ <Sr ΔC char

'char follows.

If e.g. B. the capacity ratio of capacities, the mean value of which is 10 fF, is to be determined and we assume about 1% for the maximum error I (ΔC _char / ^ -,.) _Max I, this means for capacities with deviations from z. B. ± 0.1% (10.01 fF and 9.99 fF), ± 1% (10.1 fF and 9.9 fF), or ± 10% (11 fF and 9 fF) that instead of the true results the values ± 0.099%, ± 0.99% , or ± 9.9% can be determined.

Provided that an arrangement according to FIG. 2 or 3 is used for the evaluation of capacity ratios (whereby the relative spread of the measured values σ (C _char / C _char ), ie the absolute spread σ (C _C har) normalized to the mean value C ^ -, is of interest), the error of this spread corresponds exactly to the measurement error (ΔC _char / C ^.).

Such an error is negligible for the vast majority of applications of this type.

Claims

claims

1. A circuit arrangement for evaluating the capacity of a matrix, which in at least one dimension, a plurality of rows (12, 13) with at least one capacitance (C _C har) on ^¬ has, with

a test branch (2) which is connected to first electrodes of each of the capacitors (Cchar) to be evaluated and with which two different potentials (Ni, V ₂ ) can be applied to the first electrodes;

a measuring branch (3) which is connected to second electrodes of each of the capacitances (C _cha r) to be evaluated and which has a first measuring path and a second measuring path which are connected to a common potential (V ₀ ), the first measuring path being an instrument (1) for evaluating the capacitances (Cchar) and the first measuring path and the second measuring path can be connected to the second electrodes; marked by

Control means that can switch each of the capacities to be assessed (Cchar) individually to the two different potentials.

2. Circuit arrangement according to claim 1, characterized in that the control means for each dimension of the matrix of an arrangement of switching paths, each of the rows (12, 13) with capacitances (C _C har) is assigned at least one switching path, which has a control and at least one switchable by the control into which

Test branch (2) integrated control switching element (T ₅ , T ₆ , T ₇ , T ₈ ), which at least one of the two different potentials the first electrode makes a series of capacities (C _crιa r) at ^¬ can be laid.

3. Circuit arrangement according to claim 2, characterized in that the switching paths of at least one dimension for each of the capacitances (C _char ) of a row have at least one control switching element (T ₅ ) that leads to the capacitance (C _char ) part of the test branch (2) , T ₆ , T, T ₈ ).

4. Circuit arrangement according to claim 2 or 3, characterized in that the switching paths at least one dimension for each of the rows of capacitances (C _cha r) at least one in the leading to the row part of the test branch (2) integrated control switching element (T ₅ , T ₈ ) have.

5. Circuit arrangement according to one of claims 2 to 4, characterized in that the control means an address decoder (10, 11) with an individually controllable output (XOUT, YOUT) for each of the rows (12, 13) of capacitances and the controls a signal line (6, 7, 8, 9) between each output (XOUT, YOUT) and the control switching element.

6. Circuit arrangement according to one of claims 1 to 5, characterized in that an AC voltage is present on the test branch (2).

7. Circuit arrangement according to claim 6, characterized in that the AC voltage is a square wave voltage.

8. Circuit arrangement according to one of claims 1 to 7, characterized in that the test branch (2) for each of the capacitances (C _cnar ) a first test path with a first Switching element (T and a second test path with a second switching element (T ₂ ), wherein on the first test path em first potential (Vi) and on the second test path e second

Potential (V ₂ ) is present and both test paths are connected to the first electrode via a node.

9. Circuit arrangement according to claim 8, characterized in that the switching paths at least one dimension for each of the capacitances (C _cr , ar) of a row (12, 13) em integrated in the first test path control switching element (T ₅ , T ₆ ) and em m have the second test path integrated control switching element (T ₇ , T ₈ ).

10. Circuit arrangement according to claim 8 or 9, characterized in that the switching paths of at least one dimension for each row of capacitances (C _cnar ) em m the first test path integrated control switching element (T ₆ ) and em m the second test path integrated control switching element (T - exhibit.

11. Circuit arrangement according to one of claims 1 to 10, characterized in that the connection of the first measuring path via em third switching element (T ₃ ) and the connection of the second measuring path via em fourth switching element (T ₄ ) takes place.

12. Circuit arrangement according to one of claims 2 to 11, characterized in that at least one of the switching elements and / or control switching elements is em transistor.

13. Circuit arrangement according to one of claims 1 to 12, characterized in that the instrument (1) for evaluating em current measuring device.

14. _S chaltungsanordnung according to any one of claims 1 to 13, characterized in that the second measurement path has em second instrument for a further, independent of the second evaluation rating of the capacitance (C _cha r).

15. Circuit arrangement according to one of claims 8 to 14, characterized in that clock signals are provided for controlling the switching elements, which are directly and / or directly led into the switching elements.

16. Circuit arrangement according to one of claims 8 to 15, characterized in that on the first switching element (Ti) and on the second switching element (T ₂ ) there is a common alternating clock voltage and the first and second switching elements are designed so that they are of the alternating clock voltage switched alternately or can be switched.

17. Circuit arrangement according to claim 16, characterized in that the first and second switching elements have a p-MOS and an n-MOS transistor, which can be switched or switched alternately by the clock AC voltage.

18. Circuit arrangement according to one of claims 15 to 17, characterized in that it further comprises em means for generating the clock signals applied to the switching elements and optionally a clock AC voltage used from a master clock signal.

19. Circuit arrangement according to one of claims 1 to 18, characterized in that the common potential is equal to the first or the second potential.

20. Circuit arrangement according to one of claims 1 to 19, characterized in that the first or the second potential is an operating voltage and the second or the first potential is the ground.

21. A method for evaluating capacities, in particular using a circuit arrangement according to one of claims 1 to 20, with the following steps:

-Activate at least a certain, to be evaluated capacitance (C _C ha _r) a matrix in at least one dimension a plurality of rows (12, 13) comprises at least one capacitance (C _C Har),

Charging and discharging the activated capacitance to be evaluated (C _C ar) by alternately applying a first and a second, different from the first potential to a first electrode of the capacitance (C _C har) via a test branch (2) and applying a common potential to a second electrode of the capacitance (C _C har) via a measuring branch (3);

- At least one evaluation of the capacity (C _cn ar) during the loading or unloading of the capacity (C _C ha _r ) in the measuring branch (3).

22. The method according to claim 21, characterized in that the activation takes place in that the part of the test branch (2) leading to a specific capacitance (C _C har) is switched on.

23. The method according to claim 22, characterized in that the switching on of the specific part of the test branch (2) by takes place in this part of the integrated control Prufzweigs scarf (2) ^¬ sliding members (T _5, T _6, T _7, T _8), wherein for each of the dimen sions ^¬ at least em control switching element is provided.

24. The method according to claim 22 or 23, characterized in that the switching on of the specific part of the test branch by m the test branch integrated control switching elements he ^¬ follows, with at least one of the dimensions at least e control switching element (T ₆ , T ₇ ) m this specific part of the test branch is integrated and for at least one of the dimensions at least em control switching element (T ₅ , T ₈ ) m part of the test branch is integrated, which leads to a number of capacitances (C _cna r) and to which the specific part also belongs.

25. The method according to any one of claims 21 to 24, characterized in that the capacitance (C _char ) is assessed by an instrument (1) which is integrated in a first measuring path of the measuring branch (3).

26. The method according to any one of claims 21 to 25, characterized in that the evaluation is carried out by measuring a current flow tegrals through the first measuring path of the measuring branch (3) during charging or discharging of the capacitance (C. _har ).

27. The method according to any one of claims 21 to 26, characterized in that in the case of the evaluation of the capacity (C _C a) during the loading, the at least one evaluation is not carried out during the discharge and that in the case of the evaluation of the capacity (C _cha r ) during unloading the at least one evaluation is not made during loading.

28. The method according to any one of claims 21 to 27, characterized in that the common potential is applied to the second electrode via a second measuring path of the measuring branch (3), while the at least one evaluation is not carried out.

29. The method according to any one of claims 21 to 28, characterized in that the evaluation of the capacity (C _cha r) is carried out so that the entire charging process or the entire discharging process is detected.

30 Method according to one of claims 21 to 29, characterized in that it has the further step:

Second evaluation of the capacity (C _char ) during the process of unloading or charging, in which the at least one evaluation is not carried out.

31. The method according to claim 30, characterized in that the second evaluation of the capacity (C _C hcr) by em second

Measuring instrument is carried out, which is integrated in / the second measuring path of the measuring branch (3).

32. The method according to any one of claims 21 to 31, characterized in that the alternating application of the first and second potential is carried out by applying an alternating voltage to the test branch (2)

33. The method according to any one of claims 21 to 32, characterized in that the alternating application of the first and second potential by alternately connecting a first test path with a first potential and a second Test path with a second potential on the first electrode.

34. The method according to claim 33, characterized in that the connection is carried out by means of m the test paths of integrated switching elements.

35. The method according to any one of claims 21 to 34, characterized in that the first measuring path and the second measuring path are alternately applied to the second electrode.

36. The method according to claim 35, characterized in that the connection takes place by means of switching elements integrated in the measuring paths.

37 Method according to one of claims 21 to 36, characterized in that it has the further steps:

Interchanging the temporal correlation between the application of the first and second potential and the at least one evaluation during charging or discharging;

-Reassess the capacitance (C _cha r) m the measuring branch; and

-Determine the capacity (C _ch a _r ) more precisely from the two evaluations.