NL1024386C2 - Method and measuring device for determining the capacity of a capacitive electrical component connected to an integrated circuit. - Google Patents

Description

Brief indication: Method and measuring device for determining the capacity of a capacitive electrical component connected to an integrated circuit

5 DESCRIPTION

The invention relates to a method and measuring device for determining the capacity of a capacitive electrical component connected to an integrated circuit, which circuit is provided with analog connection points which can be connected to the component to be determined by means of switches.

Printed circuit boards with, for example, integrated semiconductor circuits and discrete electrical components are particularly difficult to test in practice.

Digital circuits, provided that the integrated circuits in question have been designed for this purpose, can be tested with the "boundary scan" techniques known in practice. Digital components are herein incorporated between the external and internal connection points of an integrated circuit which form a circuit through which digital signals can be pushed under the control of a suitable control module. With the help of these signals, certain functions that the circuit must fulfill on the printed circuit board can then be simulated and tested. This test technique is also known in practice under the name IEEE Std 1149.1.

For testing analog signals, such as they may occur, for example, in mixed digital and analog integrated circuits, ie integrated circuits with both digital and analog components, the so-called mixed signal circuits "mixed-signal circuits", for example for use in telecommunication systems , the well-known IEEE 1149.1 has been standard expanded 30 with testing facilities for analogue signals. This new standard is known under the acronym IEEE 1149.4 or simply "point 4" ("dot 4").

1 * 024388-

I 2 I

I An analogue I applies to the digital test fields

I module added, equipped with analog connection points that are custard analog I

I switches, i.e. semi-detector switches, with analogue I

I connecting points of the integrated circuit can be connected and I

I 5 with power supply connection points for the integrated circuit I

I applying a suitable supply voltage. Furthermore, an analog I is

I test bus circuitry provides those VLA switches with the analog I

I connection points can be connected. The whole is under the control of I

I a test control circuit in the form of a so-called TAP · ("Test Access I

I 10 Port ") controller, as known per se from IEEE Std 1149.1. I

By suitable switching of the switches 1 in the I

I integrated circuit, the connections between the analog I

I connection points and the components of the integrated circuit, the I

I so-called "core" or "core", are broken and can be compared with the analogue I

Test bus circuit test signals on the integrated circuit I

I connected electrical component or components are supplied and I

I can become signal measurements on the component or components in question

I carried out. I

I For measuring the capacity of capacity I

A number of techniques are known in practice. I

In the so-called "roll-off point" or -3dB method, the I to be determined is determined

I capacitive component via the switches 1n an RC low pass

I filter configuration included, at the input of which an alternating voltage I

I with adjustable frequency is offered. The -3dB point of the RC I

The filter is found by changing the frequency of the alternating voltage

I vary and measure the effective value of the voltage across the I

I unknown capacitive electrical component to be determined. I

I The accuracy of this measurement is highly dependent on I

I the accuracy with which the transition resistances of the various I

I switches and wiring are known, which is also the resistance of the RC I

I filter determination and parasitic capacities and the spreading capacity of the I

I 1024 ^ 86 I

f 3 measuring environment, in this case the printed circuit board. In particular for small capacities, of the order of magnitude lower than 100 pF, the measurement produces an accuracy of less than 10%, which is unacceptable for practical applications.

Another technique, known per se in practice, is the so-called I-V method in which the capacitive component to be determined is connected in series with the known resistor to the switches and the test bus circuit. The voltage across the resistor can be calculated from the applied voltage and the measured voltage across the capacitive component to be determined. In the case of a pure capacitive component, the voltage across the resistor and the voltage across capacitive component make an angle of 90 ° with each other. By means of a simple vector calculation, the voltage across the resistor can then be calculated and, since the value of the respective resistor is known, the current through the capacitor can be determined therefrom. Since the frequency of the applied alternating voltage is known, the voltage across the capacitor is measured and the current through the capacitor can be determined from the said vector calculation, the capacitance of the capacitive component in question can be calculated from this data.

This measuring method also suffers from the fact that there are variations in the transition resistances of the switches and the analog test bus, which considerably influence the accuracy of the measurement, in particular with relatively small capacitance values. Also, the frequency of the alternating voltage applied must be carefully selected due to bandwidth limitations in the switches and the integrated circuit itself.

It is therefore the object of the invention to provide a new and better method for determining the capacitance of a capacitive electrical component connected to an integrated circuit, which circuit is provided with analog connection points which can be connected by means of switches with the determine 1024386

I 4 I

I component can be connected. I

According to the invention this problem is solved thereby, I

I that the switches are successively switched for the flame

I exchange analogue terminals of electrical charge between the I

I determine component and a capacitive reference electrical component with I

I a previously known capacity, until the voltages across the I to be determined

I component and the reference component are substantially equal to each other, I

And subsequently measuring the voltage across the reference component, I

I wherein the capacity of the component to be determined is determined from the I

Known capacity of the reference component and the measured voltage across I

I the reference component. I

The invention is based on the insight that the I

I Influence of unknown resistances in the circuit between capacitors I

I components, such as transition resistors of the switches, resistors I

I 15 of the connection points and wiring can be effectively eliminated I

I by such a charge transfer between the relevant capacitance I

I components until the voltages across the components are equal I

I are. B1j equal voltages or substantially equal to each other I

I voltages, no or such a negligible current flows through the I

Concerning resistors that the voltage drop across this is zero or I

I is negligibly small. The resistors in question therefore have I

No influence on the final charge transfer between the capacitance I

I components, so that the voltage across the relevant capacitive component I

I is only a function of their capacity. Because the voltage across the I

Reference component with techniques known per se in practice I

I can be calculated very accurately, the new method according to I offers

In accordance with the invention the possibility of using a very high accuracy

I (> 95%) measuring capacities of capacitive electrical components in I

I the order of magnitude of 10 pf or higher. I

In a preferred embodiment, the method according to I

The invention characterized by the steps of: I

A) charging the component to be determined from an electrical voltage source to a voltage substantially equal to the voltage of the voltage source; b) transferring charge from the component to be determined to the reference component, until the voltages across the component to be determined and the reference component are substantially equal to each other, c) measuring the voltage across the reference component, and d) calculating the capacitance of the component to be determined from the product of the known capacity and the measured voltage divided by the difference of the voltage from the voltage source and the measured voltage.

In this embodiment, use is also made advantageously of charging the capacitive component to be determined to the voltage of the voltage source, so that here too, transition resistances in the connection between the voltage source and the component to be determined have no influence on the ultimate Amount of charge stored in the component to be determined.

In a further embodiment, the method according to the invention is characterized by the steps of: a) charging the reference component from an electrical supply source to a predetermined reference voltage; b) transferring charge from the reference component to the component to be determined, until the voltages across the component to be determined and the reference component are substantially equal to each other, c) measuring the voltage across the reference component, and d) calculating the capacitance of the component to be determined from the product of the known capacity and the measured voltage divided by the difference of the reference voltage and the measured voltage.

This embodiment has the advantage that the reference 1-30 component can be supplied from both an electrical voltage source and an electrical current source, because in the latter case the 1024386

6 I

reference voltage across the capacitive reference component with an I

suitable high-ohmic measuring circuit can be sufficiently accurate I

measured. When working with an electrical voltage source, the I

the relevant reference component will of course be loaded as long as I

5 until the voltage across the reference component is equal to the voltage I

of the electrical voltage source, so that the influence of transition I

resistances on the amount of transferred charge becomes effective again I

eliminated. I

Preferably, the one component from which has charge to I

10 the other component is transferred a capacity smaller than the I

other component. In practice, this means that In de I

In preferred embodiment, the reference component is preferably a larger one

capacity then has the component to be determined. In the further implementation I

form, with the reference component being loaded first, the I

The reference component preferably has a smaller capacity than I

determine component. I

When the capacity of the one component, from which I

charge is too small compared to the capacity of I

the other component, which receives the charge, will occasionally add I

20 transferring a charge too low a voltage across the other component I

which voltage is difficult to measure. I

In order to achieve a sufficient degree in such a situation

to obtain a precise measurement, the method according to the invention provides I.

in a still further embodiment therein, that when the capacity of I

The one component from which charge is transferred is relatively small I

relative to the capacity of the other component that is charged by the I

one component receives, the steps of loading the one component and I

transferring charge to the other component a number of times

is repeated and the capacity of the component to be determined is calculated from I

30 the known capacity, the measured voltage after the number of times transfer I

of load and the number of times that load has been transferred. I

1024386 * 7

It will be understood that the number of times charge transfer is greater as the capacity of the one component is smaller than the capacity of the other component.

In order to make the voltages across the relevant capacitive components equal to each other in accordance with the inventive idea, a sufficiently long time for charge transfer will have to be taken into account. In a yet further embodiment of the method, the time for transferring charge is determined from the RC time constants of the capacitive components concerned and the transition resistances of the switches, terminals and wiring in the charge transfer circuit. If the transition resistances are unknown, in accordance with yet another embodiment of the method according to the invention, the RC time constants can be estimated from one or more test determinations of the capacity of the component to be determined. The RC time constants thus determined then provide a good insight into the time required for transferring charge so that the voltages across the components are equal to each other.

A good estimate of the RC time constants is necessary because the switches may not be switched into a charge transfer state for such a long time that charge from one or both components starts to leak away, which of course introduces an inaccuracy within the measurement.

Because the switches are controlled in the rhythm of a time clock connected to the IEEE Std 1149.1 control circuit, the clock frequency thereof must be selected such that there is sufficient time for transferring charge between the relevant components.

In a preferred embodiment, wherein the analog test bus circuit has a first AT1 connection bus and a second AT2 connection bus, the reference component is connected to the AT2 bus 30.

The invention also provides a measuring device for 10243 bubble

Determining the capacity of a capacitive electrical component

I connected to an integrated circuit, which circuit is provided I

I of analog connection points that are connected by means of switches with the I

I component can be connected »with the characteristic» that the I

Measuring device Is adapted for switching the I in succession

I switches for exchanging the analog connection points from I

I electrical charge between the component to be determined and a capacitance I

I electrical reference component with a previously known capacity »until I

I the voltages across the component to be determined and the reference component 1n I

Are substantially equal to each other and further provided with means for I

Measuring the voltage across the reference component and means for I

I calculating the capacity of the component to be determined from the I

I known capacity of the reference component and the measured voltage across I

I the reference component. I

In a preferred embodiment, the measuring device is I

I adapted to control the switches of an IEEE Std 1149.4 I

I test circuit. I

The invention also provides control software I

I for use with a measuring device for controlling the I

I 20 switches of an IEEE Std 1149.4 test circuit »equipped with an I

I suitable control processor. I

The invention also provides a plate with printed I

I wiring »with one or more integrated circuits and I

I at least one reference capacitor with a known capacity, for I

Use in the method and measuring device as in the preceding I

I described. In particular, the invention provides a plate with I

I printed wiring »provided with at least one integrated circuit I

I with an IEEE Std 1149.4 test circuit »where the reference capacitor I

I directly connected to the test bus circuit 1s. I

The invention will be explained below with reference to the I

The enclosed drawings are explained in more detail. I

I 1024386 I

9

Figure 1 shows schematically an integrated circuit provided with a boundary-scan test circuit according to the IEEE 1149.4 standard.

Figure 2 shows schematically a part of the structure of an analog boundary-scan module of the circuit according to Figure 1.

Figure 3 schematically shows an embodiment of a measurement of the capacitance of a capacitive electrical component connected to the integrated circuit of Figure 1.

Figure 4 shows a simplified diagram of the circuit 10 of Figure 3.

Figure 5 shows diagrammatically, graphically the repeated implementation of the method according to the invention.

Fig. 6 schematically shows a plate with printed wiring and a measuring line according to the invention connected thereto.

The invention will be explained below with reference to an application in an integrated circuit provided with a boundary-scan test circuit according to IEEE Std 1149.4. Detailed data regarding this standard can be found in "IEEE Standard for Mixed-Signal Test Bus", IEEE Standard 1149.4-1999, IEEE 1999. It will be understood that the invention is not limited to use with integrated circuits provided with such a boundary circuit. scan test circuit, but essentially it can be applied to any integrated circuit provided with analog connection points which can be connected by means of switches with a capacitive electrical component to be determined and a capacitive electrical reference component. For a proper understanding of the invention, a brief discussion of an integrated circuit with a boundary-scan test circuit according to IEEE Std 1149.1 will be discussed in the first instance.

In Fig. 1, the reference circuit 1 indicates an integrated semiconductor circuit, with a so-called core 2, in which the electrical components, such as translating tower, resistors and the like 1024386

I 10 I

I are in accordance with the I outputs from the integrated circuit 1

I perform functions. I

The reference numeral 3 is a number of digital I

I input and output ports are indicated by the so-called Digital I

I 5 Boundary Modules (DBM) 4 with the corresponding Inputs and I

The output terminals of the core 2 are connected. In addition to digital I

I input and u1 output points have the integrated circuit 1 1n I

In the embodiment shown two analog Inputs and I

I starting connection points 7. 8 which respectively Analogue Boundary I

I 10 Modules (ABN) 5, 6 with the corresponding digital input and I

The output points of the core 2 are connected. In practice I

I can prevent switching with more or fewer DBMs and ABMs. I

The ABHs 5, 6 are from an internal test bus 10 with an I

Analog test bus circuit ("Test Bus Interface Circuit") (TBIC) 9 I

I IS connected. V1a an analog test access port ("Analog Test Access Port") I

I (ATAP) 11 with connection points AT1 and AT2 1 $ de I, respectively

I bump test circuit 9 of the integrated circuit 1 I

I accessible. I

The DBMs 4, the ABMs 5, 6 and the test bus circuit 9 are I

I 20 a so-called boundary scan path 13 connected to an I

I test control circuit ("Test Control Clrcultry") 12. Before the I

Test control circuit 12 supplying suitable control signals is an I

I so-called test access port (TAP) 14, with I

I connecting points TD1, TDO, TNS and TCK that from outside the integrated I

Circuit 1 can be accessed. The test control circuit 12 includes under I

I more a TAP controller, an instruction register and a decoder for the I

I across the boundary scan path 13 to the core 2 of the integrated I

Circuit 1 supplying test signals. More detailed information about I

The test control circuit 12 and the TAP 14 can be found in the "IEEE I

I 30 Standard Access Port and Boundary Scan Architecture ", IEEE Standard I

I 1149.1a-1993, IEEE 1993. I

I 1024386 11

Figure 2 shows schematically, in more detail, a part of an ABM 5, 6, wherein only the components necessary for the understanding of the invention are shown.

The ABMs 5, 6 contain a number of switches which can be controlled by the test control circuit 12, in particular half-gel switches, which are shown in FIG. 2 for simplicity as mechanical switches. With switch SD the connection between the analog connection point 7 and the core 2 can be switched on and off. With the switches SB1 and SB2 the analog connection point 7 7 can be connected to the conductors AB1 and AB2 of the internal test bus 10 respectively.

The test bus circuit 9 is provided, inter alia, with switches S5 and S6 via which the connection points AT1 and AT2 can be connected to the conductors AB1 and AB2 of the internal test bus 10, respectively. It is noted that the test bus circuit 9 has various other switching possibilities, which, however, are not important for the explanation of the invention.

The connection point 7 can further be connected via a switch SH to a first supply connection point VH of the integrated circuit 1, for example a positive supply voltage and with the switch SL the connection point 7 can be connected to a second supply connection point VL, such as for example the signal ground of the integrated circuit 1 are connected. The switch SG offers the possibility of measuring voltage at the connection point 7 through a connection point V6.

Figure 3 shows an electrical diagram based on the circuit of Figure 2 for determining, according to the invention, the capacitance of a capacitive electrical component Cx connected between the analog terminals 7, 8 of the integrated circuit 1.

According to the invention, a capacitive electrical reference component C 'is connected to the connection point AT2 to the signal ground 15 of the circuit. The reference component Cr is 1n in practice 1024386

12 I

an electric capacitor with a precisely known capacitance value. I

By means of the switch SH ", i.e. the I

switch SH associated with ABM 5, the capacitor to be determined is I

component Cx via the connection point 7 with the positive supply voltage VH I

5 of the circuit. V1a the switch SHe, that w11 say the I

switch SH of ABM 6, the capacitive component C * becomes with the I

signal earth 15 connected. It is assumed that the circuit 1 is I

connected to a supply voltage whose connection terminal VL with the I

signal earth 15 is connected. V1a switch SB2e, i.e. I

10 switch SB2 of ABM 6, and switch S6 of the test bus circuit 9 can I

the capacitive component Tx with the capacitive reference component CR I

be connected. For carrying out the method according to I

In the invention, the remaining switches of the ABM 5 »6 and the I are located

test bus circuit 9 is in the non-telling or open position. The I

15 connection of the connection points 7, 8 with the core 2 Is via the relevant I

switches SD interrupted. I

Figure 4 shows a simplified diagram of the circuit I

of figure 3, for explaining the preferred embodiment of I

the method according to the invention. Just the reference numeral 16 is an I

20, the voltage source is denoted by voltage V ', while the reference numeral 17 is I

a measuring instrument for measuring the voltage across the capacitor I

reference component C *. Although the measuring instrument 17 «such as I

for example a high ohmic voltraeter, directly with the reference component I

C 'is signed connected, it will be clear to an expert that I

25 the measuring instrument 17 only at the time of actually measuring I

voltages with the relevant reference component need be I

connected. I

According to the preferred embodiment of the method I

according to the invention, by closing the switch SH, and I

30 with switch SB1 open, the capacitive component Cx to be determined from I

the electrical voltage source 16 is charged up to the voltage VN. Notice I

1024386 I

13 that when C * to VH is charged, current no longer flows through the switch SHs and the associated wiring and connection points, so that transition resistors in the switch and the wiring have no influence on the final charge or the voltage across the capacitor. component Cx.

The 1n Cx stored charge Qx is equal to:

Qx * C, V '(1) 10 where: Cx = capacity of Cr

After Cx has been charged, the switch SHe is switched off, i.e. the connection to the voltage source 16 is broken and the switch $ B16 is switched on, for transferring charge from the capacitive component Cx to be determined to the capacitive reference component CR.

The transfer of charge from Cx to Cr will continue until the voltage across CR and the voltage across Cx are equal. At that moment no current flows through the switch SB1s and the wiring and connection points, so that even now the influence of transition resistors in the switch and the wiring have no influence on the charge transfer.

Assuming that a quantity of charge Qt is transferred from Cx to Cr, the voltage Vx over Cr and the voltage Vr over Cr: 25 (Qx - Qt) / Cx = Qt / C, B Vr = Vx (2) where: Qt »Amount of transferred charge from Cx to Cr Cr * capacity of Cr U1t (1) and (2) the unknown capacity Cx of the capacitive component Cr can now be found from: 1024386

I 14 I

I c, = cr · Vr / (V, - Vr) (3)

By measuring the voltage Vr across the I

Reference component CR after the charge transfer is between Cx and C '

I5 can be completed with equation (3) from the measured voltage Vr, the known I

Voltage VH and the known capacitance Cr of the reference component CR de I

I capacitance Cx of the capacitive component Cx to be determined are calculated. I

I Instead of loading the I to be determined first

I component Cx, the method according to the invention can also be carried out I

I10 by first being the reference component C 'to a predetermined I

I charge reference voltage. In the circuit of Figure 3, I

The closing of the switches SH5, SB26 and S6 the reference component C 'I

I are charged, with the switch SH6 of course being switched off I

I (non-conductive). Then, by opening the switch SH5 I

And closing the switch SH6 charge of the reference component C * I

I are transferred to the component Cx to be determined. In the same way I

I as explained above, the unknown capacity Cx of the I to be determined

I component Cx are calculated from: I

I 20 Cx = Cr · (V «- Vr) / Vr (4)

I Instead of applying a voltage source for the I

Charging the reference component can of course also become a current source

I applied, with the measuring instrument 17 prior to the I

The charge transfer from C "to Cx the voltage across C" is measured. In I

I formula (4) must then replace the value of the measured I instead of VH

I voltage must be entered. I

Preferably when applying the method I

I according to the invention the capacitive component, which charge of the I

I receive another capacitive component, a capacity value that is larger I

I is then the capacity value of the other component. When charge becomes I

I 1024380-15 transferred from Cx to CR, Cx must have a smaller capacity than CR. Conversely, when charge is transferred from CR to Cx, Cx will preferably have a greater capacity than C '. When the difference between the smallest and largest capacitance values is very large, after a charge transfer only a relatively small voltage will be present across the two capacitive components, which is difficult or less accurate to measure. In such a situation, the method according to the invention can be carried out a repeated number of times n. That is, the one component is charged from the power source and then transfers charge to the other component, and so on.

For the circuit as shown in Figure 4, it holds that the voltage across the reference component CR then increases stepwise, as schematically shown in Figure 5. After n steps, the voltage across the reference component CR will approach a final value.

For the circuit according to Fig. 4 it can now be written that after n repetitions the voltage vr (n) across the reference component satisfies: 2 ° ^ = <5> v '(n + x>' '' i + c 1 c 7 * v '(n> (6) 25 vr (n -1) = - f5- * V »+ · vr (n) (7) 30 I024380-

16 I

Subtracting the equations (7) and (6) gives the I

numerical equivalent of the differential equation: I

vr (n +1) - vr (n -1) * 2 · (8) I

5 I

dv (n) 1. Cx Cx. . . 1 / Cx Cx. M I

dn 2 Cr Cx + Cr 'rW 2 vCr Cx + Cr' H v 'I

10 I

Which of the standard type is: I

y '+ p (x) · y - r (x) (10) I

15 which gives a solution when the voltage at the time t 0 l

is also 0, which is the case in the method according to the invention

is because the component Cx to be determined is assumed to be uncharged I

at the start of the measurement. Therefore: I

2 ° c c I

vP (n) - (1 - e 1 ") · V" (11) I

From which Cx can be resolved, resulting in: I

25 I

ln (1- ^ 7 ln (1 -I

C, Ψ - JT - (1 - Jf * -)) -C, (12) I

30 I

1024380-17

It will be understood that for the case when first loading the reference component a similar formula for calculating the capacity of the component to be determined can be derived, upon repeated transfer of charge from the reference component to the component to be determined.

Although in the method according to the invention, transition resistors in the switches, the terminals and the wiring have no influence on the accuracy of the measurement, it will be clear to those skilled in the art that the accuracy of the measurement is indeed influenced by resistance paths to the signal earth, which cause leakage of cargo stored in Cx and CR. It is therefore necessary to switch as soon as possible after the charge transfer has been completed. that is, charge transfer from the power supply to a relevant capacitive component and charge transfer between the relevant capacitive components themselves. The time at which the charge transfer from, for example, Cx to C 'is completed, should in practice be determined from the RC-time constants of the relevant capacitive components and the transition resistances of the switches, terminals and wiring in the charge transfer circuit. If these time constants are unknown, an impression can be obtained by means of a number of test determinations about the RC time constants and the time for completing the charge transfer can be estimated approximately therefrom.

In the case of integrated circuits with boundary-scan modules, the duration of a charge transfer period is determined by the length of the boundary-scan chain and the TCK clock rate. It is therefore important to tune the clock speed hero to the time required for charge transfer.

Figure 6 schematically shows a measuring device 18 for performing the method according to the invention, provided with a control processor 19 and a measuring instrument 17, such as, for example, a 1024386 I 18

I high-ohmic voltmeter or other suitable high-ohm measuring instrument for I

Measuring voltages, as is known per se to a person skilled in the art

I is * I

The measuring instrument 18 in the embodiment shown I

Adapted to perform the method according to the invention at I

I a switching assembly consisting of a number of integrated I

I circuits 1, one or more capacitive components Cx, resistors R and I

If necessary, inductance L, on a plate with printed wiring 20, I

I wherein the components Cx> R and L are discrete components that have one or I

10 more of the integrated circuits 1 are connected. The integrated I

I circuits 1 are of the type provided with a Boundary scan I

I test circuit IEEE $ td 1149.4 with a TAP 14 and ATAP 11 connected to I

the measuring device 18. I

I The reference component CR can be placed directly on the plate with I

Printed wiring 20 is applied, for example, as a solid component I

I

for carrying out the method according to the invention, and / or In the I

I measuring instrument 18 are included. Depending on the capacitance value I

I of the component to be determined applies to the reference component for the I

I performing the preferred method according to Figure 4, which In the most I

20 practical applications a capacitance value of 1 in the order of 1 I

I pF complies. I

I Depending on the size of parasitic capacities 1n I

In the circuit, capacities of up to 10 pF with an I can be achieved with the invention

I accuracy greater than 95% can be determined and capacities with an I

Value of 100 pF or higher with an accuracy greater than or equal to I

I at 99%. I

The invention also relates to software for delivering from the measuring device 18 to the test control circuit 12 of

I suitable control commands for controlling the ABM switches

5, 6 and the test bus circuit 9, which software is loaded into the control processor 19 kah.

I 1024386

Claims (20)

Method for determining the capacity of a capacitive electrical component connected to an integrated circuit, which circuit is provided with analog connection points which can be connected to the component to be determined by means of switches, characterized in that the switches are successively are switched for exchanging electrical charge between the component to be determined and a capacitive reference electric component with a predetermined capacity for the analog terminals, until the voltages across the component to be determined and the reference component are substantially equal to each other, and then measuring the voltage across the reference component, wherein the capacity of the component to be determined is determined from the known capacity of the reference component and the measured voltage across the reference component. Method according to claim 1, characterized by the steps of: a) charging the component to be determined from an electrical voltage source to a voltage substantially equal to the voltage of the voltage source; b) transferring charge from the component to be determined to the reference component, until the voltages across the component to be determined and the reference component are substantially equal to each other, c) measuring the voltage across the reference component, and d) calculating the capacitance of the component to be determined from the product of the known capacity and the measured voltage divided by the difference of the voltage from the voltage source and the measured voltage. The method of claim 1, characterized by the steps of: a) charging the 1024386 from an electrical power source 20 reference component to a predetermined reference voltage; B) transferring charge from the reference component to the component to be determined, until the voltages across the component I to be determined and the reference component are substantially equal to each other, c) measuring the voltage across the reference component, I d) calculating the capacity of the component I to be determined from the product of the known capacity and the measured voltage divided by the difference of the reference voltage and the measured voltage. I 4. A method according to claim 3, characterized in that the electrical supply source is an electrical voltage source with a reference voltage predetermined, the reference component being charged to a voltage substantially equal to the voltage of the voltage source. I 5. A method according to claim 3, characterized in that the electrical supply source is a current source, wherein the reference voltage I is determined from measuring the voltage across the reference component I before transferring charge to the component to be determined. I 6. Method as claimed in one or more of the foregoing claims, characterized in that when the capacity of the one component of I from which charge is transferred is relatively small relative to the I capacity of the other component, that charge of the one component I receives, the steps of charging one component and transferring charge to the other component are repeated a number of times and the I capacity of the component to be determined is calculated from the known I capacity, the measured voltage after the number of times transfer of charge I and the number of times that charge has been transferred. I Method according to claim 6, characterized in that the number of charge transfer times is greater the smaller the capacity of the one component relative to the other component. I 8. Method according to one or more of the preceding claims, characterized in that the switches are switched to a charge transfer position until the leakage of charge from a component is any longer. has negligible influence within the accuracy of the determination. 9. Method as claimed in claim 8, characterized in that the time for transferring charge is determined from the RC-t1Jd constants of the relevant capacitive components and transition resistances of the switches, connection points and wiring in the charge transfer circuit. 10. Method as claimed in claim 9, characterized in that the relevant RC time constants are estimated from one or more test determinations of the capacity of the component to be determined. 11. Method according to one or more of the preceding claims, characterized in that the integrated circuit is provided with a so-called IEEE Std 1149.4 test circuit, provided with controllable switches, analog connection points, an analog test bus circuit and a control circuit for controlling the switches, for connecting an electrical component to the terminals, test buses and power supply terminals, the method being performed by connecting the reference component to the test bus circuit and switching the switches for transferring the load from and to a respective component. 12. Method according to claim 11, characterized in that the analog test bus circuit has a first AT1 connection bus and a second AT2 connection bus, the reference component being connected to the AT2 connection bus 25. A method according to claim 11 or 12, characterized in that the switches are switched in the rhythm of a time clock connected to the control circuit. 14. Measurement method for determining the capacity of a capacitive electrical component connected to an integrated circuit, according to one or more of claims 1 to 10, which 1024386 Izz II circuit 1s have analog connection points which are connected by means of II switches can be connected to the component to be determined, characterized in that the measuring device is arranged for successively II switching the switches for exchanging electrical charge between the component to be determined and an II capacitive electrical reference component with a previously known II cap until the voltages across the component to be determined and the II reference component are substantially equal to each other, and furthermore IIs provided with means for measuring the voltage across the II reference component, and means for measuring calculate the capacity of II the compone to be determined nt from the known capacity of the Il reference component and the measured voltage across the reference component. I 15. Measuring device as claimed in claim 14, characterized in that II the measuring device 1s Arranged for controlling the switches of an II IEEE Std 1149.4 test circuit for carrying out the method II as claimed in one or more of the claims 11 to 13 I Measuring device according to claim 15, characterized in that the measuring device is provided with a suitable programmed control processor for controlling the switches of the IEEE Std I I 1149.4 test circuit. I Control software for use with a measuring device I I according to claim 16, for carrying out the method according to one. or more of claims 11 to 13 when loaded into the working memory of the control processor of the measuring device. 18. A data carrier provided with control software according to I I claim 17. I 19. Printed-circuit board, provided with one or more integrated circuits and at least six reference capacitors with a known capacitance, for use in the method and measuring arrangement I I 30 according to one or more of claims 1 to 16. I 20. Printed circuit board, provided with at least one integrated circuit with an IEEE Std 1149.4 test circuit, the reference capacitor being directly connected to the analog test bus circuit. 5 1024386