CN103150077B

CN103150077B - Circuit arrangement

Info

Publication number: CN103150077B
Application number: CN201310105290.1A
Authority: CN
Inventors: 保罗·格兰德维兹
Original assignee: Suzhou Hanrui Microelectronics Co Ltd
Current assignee: Suzhou Hanrui Microelectronics Co Ltd
Priority date: 2013-03-29
Filing date: 2013-03-29
Publication date: 2020-01-03
Anticipated expiration: 2033-03-29
Also published as: CN103150077A

Abstract

The invention relates to a circuit arrangement, the terminals of which are connected to a circuit network excited by an excitation source, comprising at least one controllable power supply and at least one capacitor, and a method for connecting the terminals to the controllable power supply via the capacitor, wherein the control function of at least one output of the controllable power supply is in the range of a potential parameter of the terminals or of the excitation source. The circuit arrangement according to the invention is not only simple, but also the internal nodes of the arrangement are set for the purpose of regulating the capacitance for the use of an internal voltage source, so that the influence of parasitic elements is eliminated.

Description

Circuit arrangement

Technical Field

The invention relates to a circuit device, in particular to a high-precision different capacitance adjusting method which can be used for measuring capacitance change of fingers or other similar objects in the application of touch screens, touch panels, touch keys and the like.

Background

There are many methods of measuring the capacitance between the touch sensitive surface electrodes. One method is by measuring the capacitance between each electrode and comparing the currently measured capacitance with the previous measurement of the same electrode, this measurement being done by means of the electrodes in an oscillating circuit whose frequency is related to the capacitance of the electrodes and the frequency in a measuring circuit whose change is related to the change in capacitance of the electrodes; another approach involves electrodes in a bridge (see US2010/0315102a 1) that has a voltage change across it and can measure the voltage change between two nodes; since the change in voltage is used to calculate capacitance, a third method is not to measure the change in voltage in the bridge, but to adjust the bridge until there is no voltage difference between the two nodes, in which case the change in components in the bridge circuit can be used to measure the unknown capacitance.

Thus, the measured weight of the entire balancing circuit is not critical for the measured weight of one entity in the balancing circuit, only that the additional weight in one module matches the unknown weight in the other module. Therefore, it is not very important to measure the variable capacitance and the whole capacitance in the bridge circuit, only the change of the components in the bridge circuit is matched with the change of the capacitance of the electrode to be measured, if the bridge circuit is composed of the known capacitance and the measured electrode, the capacitance of the unknown electrode can be obtained from the relation of the known components. If several electrodes are arranged in the bridge circuit, the variation of the capacitance value can be known, and for touch detection in a capacitive touch system, the absolute value of the sensing electrodes is not important, and only the variation is needed.

Since the capacitor only transfers a variable voltage, the capacitor bridge circuit must use a variable voltage, which is currently available in principle in a variety of ways, the first being the use of an alternating voltage with a constant frequency, such as a sinusoidal voltage; the second approach is to use an abrupt voltage that can select the system from an initial balance to the next balance. The disadvantage of the first method is that for a certain physical system, its impedance is unavoidable, and the magnitude of the measured voltage depends on the value of this impedance, and all the components of the circuit comprise resistors, as well as the resistances of the lines for the inductive interface or the resistances between the switches or the electrodes. Since the response of the frequency in the capacitive circuit depends on the resistance R and the capacitance C, the second method can overcome the above-mentioned drawback, which makes the influence of these resistances disappear by the equilibrium state.

When measuring the different capacitances of the sensor electrodes, the conventional method may use three electrodes to form a bridge circuit. Referring to fig. 1, which is an abstract plan view of an embodiment schematically illustrated in fig. 1, three electrodes are connected between which three critical capacitors are connected, wherein if the three electrodes are named a, B and C, respectively, the voltage of one electrode is obtained by an external voltage source or depending on the voltages at other nodes and the capacitance values of the nodes between the electrodes, the capacitor between each electrode and a reference ground is called Cb, and the capacitor between the electrode nodes is called Cf.

Since the system can be abstracted into a common capacitor network, the capacitance between the nodes controlled by the voltage source can be ignored and does not affect other circuits. Starting with the different assumptions, if node B is activated and the values of nodes a and C are measured, a bridge circuit is obtained, please refer to fig. 2; if nodes a and C are activated and the value of node B is measured, a T-network is obtained, called an electrical balancing circuit, as shown in fig. 3, the first method is called method 0 or M0, and the second method is called method 1 or M1.

The capacitances Cb and Cf can be matched to each other if the sensor area is designed and manufactured in a good way. Then in method M0, node B is stimulated with a signal that, if not touched by a finger, will produce the same response at nodes a and C; whereas in method M1, node a is stimulated with one signal and node C is stimulated with the opposite signal, if there is no finger touch, there is no response at node B. Due to the capacitive sensing between the finger and the electrodes, the response of the circuit is no longer balanced, which is different at node a than at node C for method M0; for method M1, node B responds if the stimulus of node a cannot be cancelled by node C, which is the opposite stimulus. In order to obtain more information about the finger changing the circuit balance, the circuit is rebalanced if the amplitude of the unbalanced circuit is measured and a desired value is derived therefrom, or by adjusting the value of one or more components in the circuit to compensate for the effect of the finger. In this case, the change in the number of elements can be used as information on the degree to which the finger affects the system.

An ideal capacitor, with capacitance as its property, shows the amount of charge of this element, combined with other elements of the circuit, can be calculated for voltage according to the formula Q = CV. Where variable Q represents the amount of charge stored in the capacitor, variable C represents the capacitance of the capacitor, and variable V represents the voltage across the capacitor.

The above formula is applied in reality within a range where the capacitor can store energy due to the maximum voltage present, or other limits to limit the range so that the function is valid. Since the capacitor is a passive component, when applied in an integrated circuit environment, there is always an effect on the capacitor from the component connected to the capacitor. For example, the capacitor is connected through the semiconductor material, that is, the capacitor is connected through a diode, and the capacitor may be formed by a transistor in which the source and drain are used so that the capacitance is not fixed but depends on the voltage level. As such, when the elements such as capacitors operate in a range in which the functions of the elements can be expressed by the formula Δ Q = C Δ V.

Since all of the elements are passive elements, many methods are available when the capacitor is implemented with a variable capacitance, and some of the methods described below utilize switches in all embodiments, which are also passive elements, however, the introduction of power can affect performance resulting in the elements acting like passive capacitors. Furthermore, the above-described element does not have to be implemented as a capacitor over a period of time and in a continuous manner, but only at certain times preset properties can occur, and the invention thus describes the element.

A common way to adjust the capacitance of a capacitor is to build several smaller capacitors and connect or disconnect the capacitors so that the effective capacitance is changed. Examples are given IN fig. 4A and 4B, with an arrangement of variable capacitance C and switch S between the node IN and ground, as shown with one end connected to ground and the other end connected to node IN. The switch S1 has its own advantages and disadvantages due to the parasitic capacitance of the switch itself in the circuit, in which case the overall capacitance becomes smaller and the parasitic capacitance becomes a major portion of the overall capacitance. Since the capacitance value is difficult to control and the switch S is in series with the capacitor C, the ratio between the parasitic capacitance and the capacitor charge will determine the capacitance when the switch is closed.

For applications where at least one node of a capacitor in the circuit is expected to have a high impedance, and therefore the voltage at that node will vary depending on the capacitance of the capacitor and the amount of power stored by other components, the two nodes of the capacitor are driven by the amount of power stored in the components, and the components will vary due to the parasitic capacitance. In order to overcome these undesirable negative effects caused by parasitic capacitances, a new solution is described below.

Disclosure of Invention

The technical problem to be solved by the present invention is how to provide a circuit device capable of eliminating the influence of parasitic capacitance in a circuit.

In order to achieve the object defined above, the invention provides a circuit arrangement, the terminals of which are connected to a circuit network excited by an excitation source, comprising at least one controllable power supply and at least one capacitor and a method for connecting the terminals to the controllable power supply via the capacitor, wherein the control function of at least one output of the controllable power supply is in the range of a potential parameter of the terminal or of the excitation source.

The invention also includes a measurement system comprising a measurement object, a network of excitation sources, and a control loop, the terminal of the circuit arrangement being connected to the network of excitation sources, the control loop comprising means for sending a control signal through the connection point of the circuit arrangement, the measurement object changing the electrical properties of the network of excitation sources, the control loop substantially compensating for changes in the network of excitation sources by changing the electrical properties of the circuit arrangement.

Compared with the prior art, the circuit device is simple, and because the device is used for adjusting the capacitance and an internal voltage source, the internal node of the device is set, so that the influence of a parasitic element is eliminated.

Drawings

The present invention is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like reference numerals refer to similar elements.

FIG. 1: a bridge schematic represented by an abstract plan view of three electrodes;

FIG. 2: a first bridge circuit according to fig. 1;

FIG. 3: a second bridge circuit schematic according to fig. 1;

FIG. 4A: one existing embodiment utilizing a plurality of capacitors connected to switches;

FIG. 4B: another prior embodiment utilizing a plurality of capacitors connected to switches;

FIG. 5: a first practical embodiment of the circuit arrangement according to the invention;

FIG. 6: a second embodiment of the circuit arrangement according to the invention;

FIG. 7: a schematic connection diagram of a first circuit arrangement according to the invention;

FIG. 8: a schematic connection diagram of a second circuit arrangement according to the invention;

FIG. 9: a connection scheme of the third circuit arrangement according to the invention.

Detailed Description

In order that the invention may be better understood, several embodiments are described in detail below. It is to be understood that one skilled in the art may practice the present invention without the following embodiments, and in order to avoid obscuring the present invention, some embodiments are presented with components and line connections in the form of block diagrams.

Herein, the finger as the capacitance sensing source is the object to be measured by the measuring device, and the object to be measured by the measuring device is generally regarded as the finger or other suitable objects, and for convenience of reading, the "or other objects" are omitted herein.

Taking fig. 5 and 6 as an example to illustrate how the imbalance of the system due to the touch of the finger is adjusted to reach the rebalancing, a plurality of variable capacitors C are added compared with fig. 1₁、C₂、C₃、C₄、C₅And C₆To the induction electrode capacitor and C for the influence of finger induction_UT0And C_UT1Means that C is not limited thereto_UTTo which node the finger is connected, only because of C_UTIs important in that it causes an imbalance in the system, and there is no relationship to its increase or decrease.

The measurement of the electrical quantity with the capacitive bridge is carried out in two steps over several cycles.

If M0 is used, in a first step the nodes a1, B1, C1 are discharged to ground, and in a second step node B1 is raised to a high level, e.g., the power supply of the system, so that the nodes a1 and C1 are raised to an intermediate level based on the value of the capacitors connected to the nodes. If no finger is detected, nodes A1 and C1 will have the same voltage due to system balance; if a finger is detected, the nodes a1 and C1 have different voltages, and the value of one or more variable capacitors is now modified, and in a new measurement cycle, the voltage difference between the nodes a1 and C1 has changed, and the value of the variable capacitor is measured by changing the capacitance of the variable capacitor over several cycles, which causes the voltage difference between the nodes a1 and C1 to return to zero.

In the second step, the capacitive bridge can operate if there is any voltage at nodes A1 and C1, however, the sensitivity change is higher when the intermediate voltage is near the middle. By varying variable capacitors C simultaneously₁And C₂And/or varying the variable capacitor C simultaneously₃And C₄By varying the amount of charge of only one capacitor, the effect of the finger can be compensated.

If the method of M1 is used, in the first step, the node a2 is charged to a high level, such as the power supply of the system, the node B2 is charged to the reference voltage, and the node C2 is discharged to ground; in the second step, the node A2 is discharged to ground level and the node C2 is charged to the same high level as the node A2 in the first step. If no finger is detected, the node B2 will have the same voltage as the first step charging voltage due to the balance of the system; if a finger is detected, the voltage at node B2 changes, using variable capacitor C for several cycles₅And C₆By varying the capacitance value and measuring the voltage difference between the reference voltage and node B2, a variable capacitor C can be found₅And C₆The voltage difference between the node B2 and the reference voltage may return to zero.

From the above description it can be seen that by influencing the relationship between the high impedance node and the low impedance node by means of a number of controllable components, the voltage at the high impedance node can be measured, while the voltage at the high impedance node is also the result of the stimulus given to the low impedance node. In this way the low impedance node remains stable in both steps, or the low impedance node transitions from a low level in the first step to a high level in the second step, or vice versa.

Any circuit that connects two nodes in a suitable manner can work for the purposes described above because the measurement is taken at the end of the second cycle, and after the system has reached a new steady state, the same is true for the capacitor during the transition from the first step to the second, which is not ideal, but the result is correct and available by the end of the second step, so that in many cases variable capacitors are utilized.

The variable capacitor can be obtained in different ways, and many applications of integrated circuits require a specific component: and the component is a voltage control analog variable capacitor. Varactors are good solutions for tuning applications, where the measurement function in the present invention is limited by the number and size of capacitors, and other solutions using linear capacitors, such as metal-metal, metal-plastic, plastic-plastic capacitors or transistor gate capacitors, which can have large capacitance values, but the change of the capacitance value of the capacitor can only be achieved by adding or subtracting capacitor units, so that several switches are needed, and such switches control the variable capacitor as shown in fig. 4A and 4B, and the switches used are single throw switches.

The semiconductor switch uses a transmission gate circuit, a PMOS pole and an NMOS pole are connected in parallel and controlled by a gate logic signal, the source of two transistors is one joint of the switch, the drain of two transistors is the other joint of the switch, and the drains of all transistors are the other terminal of the switch. Since both the source and the drain are diffusion regions, there are all parasitic elements, including parasitic capacitance. For any node driven by the voltage source, the parasitic element does not affect the measurement result, while for high impedance nodes, the parasitic element makes the system more complex.

Since such parasitic capacitances as described above are typically present in switching circuits, in integrated circuit designs the switches are made up of transistors that are connected at one end to a capacitor and at the other end to a different node. The connection point, which can be either the gate or the source of the transistor, comprises semiconductor regions in which diodes are in principle connected in reverse, which diodes always have a non-linear capacitive characteristic, which when the switch is open means that the transistor is not conducting and the capacitor and its parasitic capacitance are still connected to one side of the transistor.

To overcome the negative effects of parasitic elements, a new solution is provided by replacing the single throw switch described above with multi-controlled switches connected to one node or the other of the capacitors. In all cases, one of the switches can be driven and parasitic capacitance cancelled by driving the node of the capacitor. Since the capacitors are typically connected to a high impedance node, any capacitor that is being converted is driven by a power supply whose voltage is related to the high impedance node voltage and must be driven by a power supply that is related to the high impedance node voltage. To achieve this, it is necessary to use a controllable power supply having at least one input terminal as a high impedance node and an output terminal connected to the high impedance node through a switch and a capacitor. This solution makes it possible to create a circuit arrangement whose input values may even be negative, which circuit arrangement is created such that the influence of parasitic capacitances is effectively eliminated.

The circuit arrangement according to the invention, which allows the effective capacitance to be varied by connecting or disconnecting the capacitor, comprises at least one controllable power supply and at least one capacitor, the terminals of which are connected to a circuit network excited by an excitation source, via which capacitor the controllable power supply can be connected to the terminals, the control function of at least one output of the controllable power supply being within the potential parameters of the terminals or the excitation source, since the capacitor is usually connected to a high-impedance node.

A simple embodiment of the invention is a circuit arrangement comprising a controllable voltage source and a capacitor, the terminal Out of the circuit arrangement being connected to a circuit network which is driven by a drive source, the controllable voltage source being connected to the capacitor and then to the terminal Out, the change in the charge of the capacitor being caused by a change in the voltage at the high-impedance node, and the change in the charge of the capacitor being Δ Q and the change in the voltage with the capacitance being Δ V_CThe relationship of (a) to (b) is as follows: Δ Q = C Δ_C，

If Δ V_INIs the voltage change of the high impedance node IN, C is the capacitor C connected to IN₁The other end of the capacitor is connected to a constant currentPressure, we can calculate the variable Q of the capacitor charge.

∆Q=C∆V_IN

If the other end of the capacitor is connected to the controllable voltage source, Δ V is used for node change_SRCShows that the voltage varies depending on the capacitor_CIs different.

∆V_C = ∆V_IN - ∆V_SRC

The change in the amount of charge is: Δ Q = C (Δ V)_IN - ∆V_SRC)。

If the voltage of the controllable voltage source is V_INα times, we can rewrite as:

∆Q = C (1 - α) ∆V_IN = (1 - α) C ∆V_IN。

in a special case, the controllable voltage source may be a voltage follower, and the value α =1, when the result is:

∆Q = C (1 - 1) ∆V_IN =0

the relation between the amount of change of charge and the amount of change of voltage can be modified by selecting a parameter of the controllable voltage source from a saturation value to a value of 0.

Another embodiment of the invention creates a circuit arrangement that is realized by the use of a set of capacitors, comprising different capacitance values, a double throw switch and a controllable voltage source or voltage follower. In this case each capacitor may be connected to a constant voltage such as ground or a controllable voltage source or voltage follower, and the set or all of the capacitors may be connected to either of the two controllable power supplies under control of the control signal, the at least one controllable power supply being controlled by the same control signal. If the capacitor is connected to the voltage follower, no voltage difference exists between the two ends, so that the effective capacitance is not increased when viewed from the application end; if the capacitor is connected to a controllable voltage source, a certain voltage difference exists between the two ends, so that the effective capacitance is partially increased from the application end. The circuit arrangement further comprises a signal control terminal TC, wherein the signal control terminal is provided with a control connection point, and a control signal can change at least one of the control functions of the controllable power supply and/or change the connection of the capacitor via the control connection point.

The control connection points may be divided into groups of signal carriers each carrying a control signal, the at least one signal carrier group constituting a group of signal carriers carrying a digital control signal, the combination of all states in the group representing the digital signal in order that each individual signal carrier carries a signal of a limited number of states, the total amount of charge flowing through the terminal being proportional to the digital control signal. The control signal may select a function, control the output of at least one of the controllable power supplies, and command a function list such that an integer value indicates the position of the function in the function list, wherein the output voltage of the controllable power supply commands the function list, the control connection point may select a function for controlling the output of at least two of the controllable power supplies, and the functions correspond to integers, with different functions corresponding to different integers.

In another embodiment of the present invention, as shown in fig. 7, the circuit device is composed of two controllable voltage sources, a capacitor bank with different capacitance values, and a double-throw switch, wherein the terminal Out of the circuit device is a high-impedance node connected to a circuit network excited by an excitation source; one end of the capacitor is connected to the terminal Out, the other end of the capacitor is connected to the controllable voltage source, the capacitor is connected with the controllable voltage source through a double-throw switch S, one input end of the double-throw switch S is connected with a high level output by the controllable voltage source, and the other input end of the double-throw switch S is connected with a low level output by the other controllable voltage source. The excitation source is connected with a controllable voltage source, the double-throw switch S is connected with a capacitor C and then outputs the voltage to the controllable voltage source, the control function of at least one output end of the controllable voltage source is within the potential parameter range of the terminal Out or the excitation source, and the control signal can change the control function of at least one controllable power source and/or change the connection of the capacitor through the connection point of the signal control end TC.

In such an embodiment, one or the other controllable voltage source is connected to a capacitor C via a switch S, the interval between the two controllable voltage sources being settable and the circuit arrangement being settable in said interval via the switch S, the effective capacitance being changed by connecting or disconnecting said capacitor. In another embodiment of the present invention, as shown in fig. 8, the circuit device is composed of a voltage follower, a capacitor C set with different capacitance values, and a double-throw switch S, different from the embodiment of fig. 7: one input end of the double-throw switch C is connected with the high level output by the voltage follower, and the other input ends of the double-throw switch C are grounded.

In yet another embodiment of the invention, as shown in fig. 9, the one controllable power supply comprises a voltage follower, a plurality of resistors R having nodes at least at ends of the resistors, one input of the voltage follower being connected to the terminal, one end of the plurality of resistors R being driven by an output of the voltage follower, and a switching network SR selecting one node as an output of the controllable power supply under control of the control connection point. In contrast to the example of fig. 7: one of the controllable voltage sources is replaced by a voltage follower and a complex path having a plurality of single throw switches S connected to the capacitor C node by selecting one of the resistor nodes, respectively, and the other ends of the plurality of resistors R are driven by a constant voltage, an excitation source or at least one controllable power source. The output control function of the controllable power supply comprises a plurality of parameters such as an excitation source and a signal control end.

In the above embodiment, only one controllable voltage source is composed of a voltage follower, a plurality of resistors and a switch network, and since the principle is the same, another controllable voltage source may also be replaced by the voltage follower and other elements, that is, at least two controllable voltage sources include at least one voltage follower, a plurality of resistors having nodes at the ends of at least one resistor, and a switch network, one input end of the voltage follower is connected to the terminal, one end of the plurality of resistors is driven by the output of the voltage follower, and the switch network selects one node as the output of one controllable voltage source and one of the nodes as the output of another controllable voltage source under the control of the control connection point, and since a plurality of circuit diagrams may be extended, detailed description thereof will not be repeated one by one.

IN the present invention, since the use of a reference voltage such as ground is not essential, it is possible to connect the circuit arrangement between the high impedance node IN and the low impedance node such as ground to operate on the same principle if the low impedance node is a variable voltage node. Referring to fig. 5 and 6 of the above embodiment, it may be substituted for a variable capacitor C between ground and node a1 or C1₃And C₄However, by replacing the ground node by a variable node, the variable capacitor C is also provided for the node B1 in method M0 or the node a2, the node C2 in method M1₁、C_2、C₅And C₆May be replaced by said circuit arrangement.

In theory, the use of a voltage follower necessarily involves the output of the follower being equal to the input of the follower, only the current drive circuit being independent of the input, however in practical applications the follower will have a deviation that causes a voltage difference between the input and the output. For the use of voltage followers, connecting the capacitor to the follower via a switch will not give the desired result, since a voltage difference still exists across the capacitor, which difference will cause the circuit arrangement to be affected considerably, especially for small-value arrangements, which may cause great errors if two circuit arrangements are used in a bridge, since each has their own offset. However, when applied in a bridge circuit, the initial balance does not depend on the absolute values of the elements, and since the initial bridge balance is obtained without external touch such as a finger, while the value of the voltage is set to the maximum value in the circuit device, in this configuration, the internal capacitance of the variable capacitance circuit has the maximum voltage, and thus small deviations have little effect. For the initial balancing, to compensate for the effect of the finger-like capacitance in the capacitive bridge, the value of the circuit arrangement is changed and reduced, in which case the total amount of the reduction corresponds to the capacitance generated after the finger touch.

In the present invention, the capacitance values of the capacitor groups are set according to levels, wherein the first capacitor has a unit capacitance value, and each next capacitor has a capacitance value equal to the sum of the capacitance values of the preceding capacitors. In all embodiments of the present invention, the controllable power source is illustrated as a controllable voltage source, but is not limited to this embodiment, and any circuit arrangement capable of changing the effective capacitance by connecting or disconnecting the capacitor is within the scope of the present invention.

The invention also includes a measurement system comprising the circuit arrangement, the measurement system comprising a measurement object, a network of excitation sources, and a control loop, the terminals of the circuit arrangement being connected to the network of excitation sources, the control loop comprising means for sending control signals through the connection points of the circuit arrangement, the measurement object changing the electrical properties of the network of excitation sources, the control loop substantially compensating for changes in the network of excitation sources by changing the electrical properties of the circuit arrangement.

Claims

1. A circuit arrangement having terminals connected to a circuit network excited by an excitation source, characterized in that: the circuit arrangement comprises at least one controllable power supply and at least one capacitor, one end of the capacitor is connected to the terminal, the other end of the capacitor is connected to the controllable power supply, the excitation source is connected to a controllable voltage source, and the output of the capacitor is connected to the controllable voltage source, wherein the control function of at least one output end of the controllable power supply is within the potential parameter range of the terminal or the excitation source.

2. The circuit arrangement of claim 1, wherein: the control function of the at least one controllable power source is within the limits of the excitation source.

3. The circuit arrangement of claim 1, wherein: the circuit arrangement further comprises a signal control terminal provided with a control connection point, wherein a control signal can change the control function of at least one of the controllable power supplies and/or change the connection of the capacitor via the control connection point.

4. The circuit arrangement of claim 1, wherein: the potential of the terminal is changed by changing the control function of the controllable power supply and/or changing the connection of the capacitor.

5. A circuit arrangement as claimed in claim 3, characterized in that: the capacitor may be disconnected from one of the controllable power supplies and connected to the other controllable power supply under control of the control signal.

6. A circuit arrangement as claimed in claim 3, characterized in that: the control signal may select a function, control the output of at least one of the controllable power supplies, and command the list of functions such that an integer value indicates the position of the function in the list of functions.

7. The circuit arrangement of claim 6, wherein: the output voltage of the controllable power supply commands the list of functions.

8. The circuit arrangement of claim 6, wherein: the control connection point may be adapted to selectively control at least two of the functions of the controllable power supply output, and the functions correspond to integers, with different functions corresponding to different integers.

9. A circuit arrangement as claimed in claim 3, characterized in that: at least one controllable power supply comprises a follower, a plurality of resistors and a switch network, wherein the resistors are at least provided with nodes at the end parts of the resistors, one input end of the follower is connected to the terminal, one ends of the resistors are driven by the output of the follower, and the switch network selects one node as the output of the controllable power supply under the control of the control connection point.

10. A circuit arrangement as claimed in claim 3, characterized in that: the at least two controllable power supplies comprise at least one follower, a plurality of resistors with nodes at the end of at least one resistor, and a switch network, wherein one input end of the follower is connected to the terminal, one end of the plurality of resistors is driven by the output of the follower, and the switch network selects one node as one under the control of a control connection point and one of the nodes as the other output of the controllable power supply.

11. A circuit arrangement as claimed in claim 9 or 10, characterized in that: the other ends of the resistors are driven by constant voltage.

12. A circuit arrangement as claimed in claim 9 or 10, characterized in that: the other ends of the resistors are driven by the excitation source.

13. A circuit arrangement as claimed in claim 9 or 10, characterized in that: the other ends of the resistors are driven by at least one controllable power supply.

14. A circuit arrangement as claimed in claim 9 or 10, characterized in that: the output control function of the controllable power supply is such that at least the excitation source is used as a parameter.

15. The circuit arrangement of claim 1, wherein: and a set of the capacitors, the capacitance values of the capacitor sets being set according to a hierarchy, wherein a first capacitor has a unit capacitance value, and each next capacitor has a capacitance value equal to the sum of the capacitance values of its preceding capacitors.

16. A circuit arrangement as claimed in claim 3, characterized in that: one or all of the capacitors may be connected to either of the two controllable power supplies under control of the control signal.

17. A circuit arrangement as claimed in claim 3, characterized in that: the at least one controllable power supply is controlled by the same control signal.

18. A circuit arrangement as claimed in claim 3, characterized in that: the control connection points may be divided into groups of signal carriers, each group of signal carriers carrying a control signal.

19. The circuit arrangement of claim 18, wherein: the at least one signal carrier group constitutes a set of signal carriers carrying digital control signals, the combination of all states in the set representing the digital signals, in order that each individual signal carrier carries a signal of a limited number of states.

20. The circuit arrangement of claim 19, wherein: the digital control signal is proportional to the total amount of charge flowing through the terminal.

21. A circuit arrangement as claimed in claim 3, characterized in that: the signal response of the terminal may be compensated by a control signal.

22. A circuit arrangement as claimed in any one of claims 1 to 4, characterized in that: the controllable power supply is a voltage supply.

23. A measuring system comprising a circuit arrangement according to any one of claims 1 to 4, the measuring system comprising a measurement object, a network of excitation sources and a control loop, characterized in that: the terminals of the circuit arrangement are connected to the stimulus network, the control loop includes means for sending a control signal through the connection points of the circuit arrangement, the measurement alters the electrical properties of the stimulus network, and the control loop substantially compensates for changes in the stimulus network by altering the electrical properties of the circuit arrangement.