TWI451094B - Compensating circuit having programmable capacitance array for measuring ac voltage - Google Patents

Description

Compensation circuit for AC voltage measurement with programmable capacitor array

The invention relates to a compensation circuit. In particular, there is a compensation circuit for AC voltage measurement and having a programmable capacitor array.

An AC voltmeter is a device that is very common in everyday life. Traditionally, AC voltmeters use a resistor divider with large impedance and including several capacitors. Naturally, the AC voltmeter becomes a low pass filter. For AC power supplies with frequencies above 500 Hz, the accuracy of the measurements is not as high due to signal strength degradation.

See Figures 1A and 1B. Figure 1A shows a conventionally designed AC voltmeter comprising two resistors R1 and R2 and a capacitor C1 for use as a resistor divider to form a detection unit to obtain the AC voltage for use as Further measurement. Figure 1B shows how this signal strength changes with the frequency of the AC power source. Obviously, the signal strength is attenuated above 1 kHz. When the frequency exceeds 10 kHz, the AC voltmeter is difficult to use for the measurement of the AC voltage.

For some high-order AC voltmeters, the detection unit needs to be well designed to mitigate this. Referring to Figures 2A and 2B, two capacitors C2 and Cs are used in the design, where Cs is a variable capacitor. Thus, such a design can be used to measure a wide frequency AC voltage source.

Traditionally, the variable capacitor can be implemented according to different frequencies of the AC voltage source. One way to compensate for the frequency is to manually change the external capacitor of the AC voltmeter. However, when the capacitance value is changed by a jumper, additional solder residue is caused. Because of problems such as temperature and humidity, the capacitance value can easily cause instability. The capacitance value of the external capacitor will also be affected by different batches of PCBs with different correction values. If the AC voltmeter needs to be finalized by the line staff after assembly, the cost of the product will increase and the accuracy will decrease.

European Patent Publication No. EP 2,386,868, which is directed to a method for overcoming the above problems: applying a known volt signal across a first and second input to a capacitive voltage divider circuit; measuring one across a third capacitor a first volt value of the first and second plates; determining a conversion function that is to be operated to change the measured volt value; configuring the compensation circuit with the determined conversion function; and the volt measurement circuit A high voltage alternating current signal is measured together such that the compensation circuit can perform a change in the one volt value of the switching function received in response to the decision and provide the changed voltage value at its output.

Although the conversion function and the compensation circuit can be used to obtain a more accurate result of a high AC voltage, it cannot be applied to a smaller range of volt values.

Therefore, an AC voltmeter can measure voltage over a wide frequency range and maintain research and development.

This paragraph of text extracts and compiles some features of the present invention; other features will be Described in the following paragraphs. Its purpose is to cover the spirit and scope of the subsequent patent scope, different retouching and similar arrangements.

According to one aspect of the invention, a compensation circuit includes: a pair of first wires for connecting to an AC circuit; and a variable capacitor electrically connected to the first wire for conforming to a programmable capacitor array And providing a different capacitance value; and a control unit electrically connected to the first wire for changing a capacitance value of the variable capacitor according to an external command to a capacitance value of a capacitor of the programmable capacitor array.

According to the present concept, the control unit further includes a pair of second wires for receiving the external command.

According to the concept of the present invention, the external command is provided by software in a notebook computer or a desktop computer.

According to the present concept, the programmable capacitor array provides different capacitance values, which is equivalent to Where ACC[n] is a BIT array containing numbers 0 and 1, m is a parameter, m is a recursive parameter, Cap is a unit capacitance, and the capacitance value is in the form of a picofarad (pF).

According to the present concept, the unit capacitor (Cap) has different values in different wafer processes.

According to the present concept, the unit capacitance (Cap) is 0.2.

The invention will be more clearly described with reference to the following examples. Please note that the following description of embodiments of the invention is only intended to describe the application; this is not meant to be The invention has been described or illustrated in detail in the form of the disclosure.

An embodiment of the invention is depicted in Figures 3 through 6. Figure 3 shows an embodiment of the invention. Figure 4 depicts how this embodiment can be applied to an AC voltmeter. Figure 5 shows the structure of a programmable capacitor array. Figure 6 shows the flow of operating a capacitor in accordance with the present invention.

Please refer to Figure 3. According to the embodiment, a compensation circuit 10 includes a pair of first wires 101, a variable capacitor 102, a control unit 103, and a pair of second wires 104. The first wire 101 is used to connect to an alternating current circuit (not shown). What is emphasized here is the manner in which the first wire 101 is connected to the alternating current circuit, either directly or indirectly. The direct way is to contact the AC circuit without any other components such as resistors in between. Otherwise, other elements may be present between the first wire 101 and the alternating current circuit in accordance with the spirit of the present invention.

The variable capacitor 102 is electrically coupled to the first lead 101 and provides a different capacitance value in accordance with a programmable capacitor array. The control unit 103 is electrically connected to the first wire 101 for changing the capacitance of the variable capacitor to a capacitance of the programmable capacitor array according to an external command. The second wire 104 can accept the external command from the outside, it should be noted that the external command is provided by a software in a notebook or desktop computer. In the present embodiment, by the software installed in a desktop computer 20, the user can command the control unit 103 to obtain different capacitance values from the variable capacitor 102. If feasible, the components within the dashed line can be integrated into an integrated circuit (IC) for modular application.

Before describing the operation of the compensation circuit 10, please refer to FIG. This figure depicts how the compensation circuit 10 is applied to the example of FIG. 2A. All the originals in Fig. 2A are placed in Fig. 4 except for the replaced capacitor Cs. One can easily understand that the compensation circuit 10 is connected to an existing AC voltmeter via the first wire 101 and uses the second wire 104 to receive an instruction from the desktop computer 20. On the contrary, the compensation circuit 10 plays the same role as the variable capacitor Cs in Fig. 2A.

Please refer to Figure 5 and Figure 6. The programmable capacitor array provides different capacitance values, equivalent to the equation Value. M is a recursive parameter. It is used to describe a mathematical calculation state when different variables are transformed. ACC[n] is a BIT array. As shown in Figure 5, it contains a series of 0s and 1. The value of N is changed from 0 to 6, and the BIT value is also changed. Therefore, each ACC[n] value can be one of 0X0000000 to 0X1111111. A total of 27,128 arrays can be used to obtain different capacitance values. M is a parameter. In this embodiment, m is 6. Cap is a unit capacitor. In practice, 0.2 is a preferred value. In accordance with the spirit of the present invention, the unit capacitance Cap has different values in different wafer processes. It is not limited to 0.2. According to this embodiment, the unit of the capacitance value is a picofarad (pF).

Please refer to Figure 6, which shows the process of operating the capacitance value in a table. When the user uses the desktop computer 20 to command the compensation circuit 10, he can simply select any one of the ACC[n] from the screen and transmit the decision to the control unit 103, a capacitor. The value is obtained. ACC[n] is selected as 0X1010101. The sum of the operations is 91.2. That is, 91.2 pF is provided by the compensation circuit 10.

It should be understood that the application of the present invention is to use a capacitor digitally programmable array within a wafer set. The user uses the software by clicking on the screen with a desktop computer, laptop or other device to properly fine tune the value of the compensation capacitor. It has the advantage of being free from the disadvantages of manually replacing external capacitors.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the invention, and any one of ordinary skill in the art can make some modifications and refinements without departing from the spirit and scope of the invention. The scope of the invention is defined by the scope of the appended claims.

10‧‧‧Compensation circuit

101‧‧‧First wire

102‧‧‧Variable Capacitors

103‧‧‧Control unit

104‧‧‧Second wire

20‧‧‧ desktop computer

Figure 1A shows a conventional AC voltmeter.

Figure 1B is a diagram showing the relationship between signal strength and frequency of the conventional AC voltmeter.

Figure 2A shows another conventional AC voltmeter.

Figure 2B is a diagram showing the relationship between signal strength and frequency of another conventional AC voltmeter.

Figure 3 shows an embodiment of the invention.

Figure 4 depicts how this embodiment can be applied to an AC voltmeter.

Figure 5 shows the structure of a BIT array.

Figure 6 shows the flow of operating a capacitor in accordance with the present invention.

10‧‧‧Compensation circuit

101‧‧‧First wire

102‧‧‧Variable Capacitors

103‧‧‧Control unit

104‧‧‧Second wire

20‧‧‧ desktop computer

Claims (4)

A compensation circuit for AC voltage measurement and having a programmable capacitor array includes: a pair of first wires for connecting to an AC circuit; and a variable capacitor electrically connected to the first wire for Providing different capacitance values according to the programmable capacitor array; and a control unit electrically connected to the first wire and including a pair of second wires for receiving an external command to change the external command according to the external command The capacitance of the variable capacitor is the capacitance of a capacitor of the programmable capacitor array, wherein the programmable capacitor array provides different capacitance values, which is equivalent to Where ACC[n] is a BIT array containing numbers 0 and 1, m is a parameter, n is a recursive parameter, Cap is a unit capacitance, and the capacitance value is in the form of a picofarad (pF). The compensation circuit of claim 1, wherein the external command is provided by a software in a notebook computer or a desktop computer. The compensation circuit of claim 1, wherein the unit capacitor (Cap) has different values in different wafer processes. The compensation circuit of claim 1, wherein the unit capacitance (Cap) is 0.2.