KR19980079059A - Circuit to increase the capacity of the capacitor - Google Patents

Abstract

A circuit is disclosed that can increase capacitor capacity to allow the effect of large capacitors as small capacitors. The capacitor is charged to a predetermined capacitance by the voltage applied by the power supply voltage source. The first transistor provides a high current to increase the capacitance of the capacitor. The current source provides a constant current to the base electrode and the emitter electrode of the first transistor to keep the first transistor operational at all times.

Description

Circuit to increase the capacity of the capacitor

The present invention relates to a circuit for increasing the capacity of a capacitor. More specifically, the present invention relates to a capacitance increasing circuit of a capacitor for increasing the capacitance of a capacitor so as to obtain the effect of a large capacitor as a small capacitor.

1 is a circuit diagram illustrating a conventional charging of a capacitor, and FIG. 2 is a graph of current versus time in the circuit of FIG. 1.

Referring to FIG. 1, two opposing first and second metal plates 100, 102 are separated by insulator 104. The first metal plate 100 is connected to the positive electrode of the battery 106, and the second metal plate 102 is connected to the negative electrode of the battery 106. The switch S is connected between the second metal plate 102 and the cathode of the battery. When the switch is closed at time t = 0, the following occurs:

1. The 'electric force' of the battery 106 is accumulated in the second metal plate 102 by pushing electrons counterclockwise from the first metal plate 100 in FIG. At this time, the second metal plate 102 is said to have a capacity to store electrons.

2. As shown in FIG. 2, at the time t = 0, the current flow is maximized and gradually falls to zero. The amount of initial current depends on the circuit voltage and the size of the resistor. Even if there is no resistor in the circuit, the initial amount of current is limited by the smaller wire resistance and internal battery resistance. If the resistance of such a circuit is R, the initial current is V / R at t = 0 as shown in FIG.

3. In FIG. 1, the metal plate has the same potential difference as the battery voltage (V). The electric field indicated by the arrow in FIG. 1 exists from the first metal plate 100 up to the second metal plate 102, and the strength of the electric field depends on the voltage and distance between the metal plates. The battery 106 is charged with the metal plate and thus contains energy between the metal plates, which keeps the energy accumulated until released. However, when the battery 106 is removed and shorted in FIG. 1, electrons collected in the second metal plate 102 return to the first metal plate 100, and the electric field becomes weaker. In other words, the energy stored in the electric field is lost in the form of heat (P = I ² R) as much as I ² R due to the resistance R of the wire, and returns to the state before closing the switch (S). As described above, an element in which two metal plates 100 and 102 are separated by a nonconductor (derivative) is called a capacitor. The capacitance C of the capacitor is as follows.

[Equation 1]

C = ε ₀ · ε _r A / d

Where C is the capacitance, the unit is farad (F), ε ₀ is the permittivity of the free space, ε _r is the relative permittivity of the dielectric of the capacitor, and A is the area of the metal plate in square square meters (m 2) And d is the distance between the metal plates and the unit is m.

It can be seen from Equation 1 that the capacitance of the capacitor is proportional to the area of the metal plate and inversely proportional to the distance between the metal plates. Therefore, doubling the metal plate area doubles the capacitance, and doubling the space of the metal plate reduces the capacitance by half.

Capacitor Is defined by the vi relation. But usually The maximum and minimum values are limited by the circuit. Therefore, the excess current does not represent the characteristics of the capacitor. Capacitors are often used with resistors to form filters such as low pass filters (LPFs) and high pass filters (HPFs). However, the band of such a filter is determined by the value of R × C. Therefore, when associated with low frequencies, R, C, or both must be made large. However, since the R value is limited to increase in relation to the input / output resistance of the circuit, the value of C must be increased to obtain a larger R × C value. For example, to make a primary LPF with 1 kHz at 3 dB, 2πRC = 1/1000. Therefore, when R = 100 kΩ, C ~ A capacitor of about 1.59 nF is required.

However, since the capacitor used in the integrated circuit (IC) is not used more than 100pF in reality, it is common for the LPF as described above to use an external large capacitor. In this case, a separate pin is required to connect the capacitors, and an increase in the complexity of the application circuit and the cost increases due to the addition of external devices.

3 shows a conventional low pass filter 30, and FIG. 4 shows a board diagram of the transfer function of the low pass filter 30 shown in FIG. 3. The conventional low pass filter 30 is composed of a capacitor (C) connected in one end to the ground and the other end connected to the output terminal and a resistor (R3) connected in parallel to the capacitor (C). The output voltage Vout of the conventional low pass filter 30 depends on the frequency of the input current Hz. Their relationship is shown in FIG. In Figure 4, the vertical axis represents the output voltage (Vout), the horizontal axis represents the frequency (Hz) of the input current.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object thereof is to provide a capacitor capacity increasing circuit for increasing the capacitance so as to obtain the effect of a large capacitor as a small capacitor.

1 is a circuit diagram illustrating a conventional charging of a capacitor.

FIG. 2 is a graph of current versus time change in the circuit of FIG. 1.

3 is a circuit diagram of a conventional low pass filter.

4 is a board diagram of the transfer function of the low pass filter shown in FIG.

5 shows a configuration of a circuit for increasing the capacity of a capacitor according to an embodiment of the present invention.

FIG. 6 is an equivalent circuit showing that the high capacitance capacitor shown in FIG. 5 acts as a low pass filter.

FIG. 7 is a board diagram of the transfer function of the low pass filter shown in FIG. 6.

FIG. 8 is a circuit diagram showing the configuration of a low pass filter having the circuit shown in FIG.

FIG. 9 is an equivalent circuit of the low pass filter shown in FIG. 8.

10 is a board diagram of the transfer function of the low pass filter with high capacitance shown in FIG.

Explanation of symbols on the main parts of the drawing

30, 60, 80: low pass filter 50: capacitor capacity increase circuit

100, 102: metal plate 104: insulator

106: battery 500, 800: current source

502, 504, 802, 804: constant current source

In order to achieve the above object, the present invention provides a base electrode connected to one end of the capacitor and a collector electrode at the other end of the capacitor to increase the capacitance of the capacitor charged to a predetermined capacitance by a voltage applied by a power supply voltage source. A first transistor coupled to provide a high current; And a current source for providing a constant current to the base electrode and the emitter electrode of the first transistor so as to keep the first transistor in an operational state at all times.

In the present invention, by increasing the capacity of the capacitor having a small capacity to obtain the effect of the capacitor having a large capacity, it is possible to reduce the area occupied by the capacitor in the IC.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

5 shows a configuration of a circuit 50 for increasing the capacitance of a capacitor according to an embodiment of the present invention. The capacitor capacitance increasing circuit 50 according to the present invention includes a capacitor C, a first NPN transistor Q1 and a current source 300. The capacitor C is charged to a predetermined capacitance C by the voltage applied by the power supply voltage source Vs. The first NPN transistor Q1 has a base current connected to one end of the capacitor C and a collector electrode connected to the other end of the capacitor C so as to increase the capacitance of the capacitor C to βC. gives β.

The current source 500 provides a constant current to the base electrode and the emitter electrode of the first NPN transistor Q1 in order to keep the first NPN transistor Q1 always in an operating state. The current source 500 is connected between one end of the capacitor C and the base electrode of the first NPN transistor Q1 and the power supply voltage source Vs to supply a constant current to the base electrode of the first NPN transistor Q1. 1 constant current source 502, a second NPN transistor Q2, in which the collector electrode is connected to the emitter electrode of the first NPN transistor Q1, and the emitter electrode is connected to the power supply voltage source Vs, and the second NPN transistor Q2. In order to control the current flowing in the collector electrode of the first end is connected to the power supply voltage source Vs in common with the first constant current source 502 and the other end is connected to the base electrode of the second NPN transistor Q2 to the second NPN transistor Q2 And a second constant current source 504 for supplying a current equal to the current supplied to the base electrode of the first NPN transistor Q1 to the base electrode. The contact between the emitter electrode of the first NPN transistor Q1 and the collector electrode of the second NPN transistor Q2 is connected to a load, and the contact between the emitter electrode of the second NPN transistor Q2 and the power supply voltage source Vs is grounded. .

Hereinafter, the operation of the capacitor capacitance increasing circuit 50 according to the present invention will be described.

In the transistor Has a relationship. Therefore, when the capacitor is connected to the base electrode side of the transistor Wow Looking at the relationship of,

of Have a relationship. here Is almost constant voltage (about 0.7V). At this time, when viewed from the emitter electrode side of the first NPN transistor Q1, the original capacitance C is increased by (β + 1) times. But from above And the assumption that β is a constant. This has the premise that the emitter current must always flow through the transistor and that the rate of change (maximum current / minimum current) of this current is too large (eg more than 100 times). In order to satisfy this condition, a current component irrespective of a signal must always flow through the transistor. In this case, a current continues to flow through the capacitor C to supply a base current.

Another problem is that since the base current of the first NPN transistor Q1 always flows in the same direction, the current charged in the capacitor C also continues to flow in only one direction. Accordingly, in the current source 500, when the bias current of the first NPN transistor Q1 flows, the second NPN transistor Q2 and the second NPN are connected to the base electrode of the first NPN transistor Q1 by the first constant current source 502. The constant current source 504 supplies the same constant current to the emitter electrode of the first NPN transistor Q1 so as to always operate the first NPN transistor Q1 in the active region and at the same time to flow the DC current component through the capacitor C. Remove it.

FIG. 6 shows that the high capacitance capacitor shown in FIG. 5 acts as a low pass filter 60 composed of a high capacitance capacitor βC and a parasitic resistor R ₀ connected in parallel to the high capacitance capacitor βC. . FIG. 7 is a board diagram of the transfer function of the low pass filter shown in FIG. 6. In Figure 7, the vertical axis represents the output voltage (Vout), the horizontal axis represents the frequency of the input current. As shown in FIG. 7, it can be seen that the low pass filter 60 shown in FIG. 6 operates at a lower frequency than the conventional low pass filter 30 shown in FIG.

8 is a circuit diagram illustrating a configuration of a low pass filter in a capacitor capacitance increasing circuit according to an exemplary embodiment of the present invention. FIG. 9 is an equivalent circuit diagram of the low pass filter with the high capacitance shown in FIG. 8. 10 is a board diagram of the transfer function of the low pass filter with high capacitance shown in FIG. In FIG. 10, the vertical axis represents the output voltage Vout, and the horizontal axis represents the frequency of the input current. In the low pass filter 80 having a high capacitance capacitor according to an embodiment of the present invention, the capacitor C is charged to a predetermined capacitance by a voltage applied by the power supply voltage source Vs. The first NPN transistor Q81 has a base current connected to one end of the capacitor C and a collector electrode connected to the other end of the capacitor C so as to increase the capacitance of the capacitor C. To provide.

The current source 800 provides a constant current to the base electrode and the emitter electrode of the first NPN transistor Q1 to maintain the first NPN transistor Q1 at all times. The current source 800 is connected between one end of the capacitor C and the base electrode of the first NPN transistor Q81 and the power supply voltage source Vs to supply a constant current to the base electrode of the first NPN transistor Q81. 1 constant current source 802; A second NPN transistor Q82 having a collector electrode connected to the emitter electrode of the first NPN transistor Q81 and the emitter electrode connected to the power supply voltage source Vs; And supplying a current equal to the current supplied to the base electrode of the first NPN transistor Q81 to the base electrode of the second NPN transistor Q82 to control the current flowing through the collector electrode of the second NPN transistor Q82. A second constant current source 804 is provided. The resistor R8 is connected in parallel with the second NPN transistor Q82 and the third current source 806. The low pass filter 80 having the high capacitance capacitor according to the embodiment of the present invention configured as described above has a frequency characteristic as shown in FIG. 10 and operates at a lower frequency than the conventional low pass filter shown in FIG. It can be seen.

4, 7, and 10, a capacitor pass increasing circuit 60 according to an embodiment of the present invention, a low pass filter 80 having a capacitor capacity increasing circuit according to an embodiment of the present invention, and It can be seen that the operation in the low-frequency signal in the order of the conventional low pass filter 30.

As described above, in the present invention, the capacity of a small capacitor can be increased to obtain the effect of a capacitor having a large capacity. Inside an IC, a capacitor typically occupies a large area. By taking the effect of a large capacitor as a small capacitor, the required capacitor area can be reduced.

Although this invention was demonstrated concretely by the said Example, this invention is not restrict | limited by this, A deformation | transformation and improvement are possible within the range of common knowledge of a person skilled in the art.

Claims (6)

A base electrode is connected to one end of the capacitor C and a collector electrode is connected to the other end of the capacitor C to increase the capacitance of the capacitor C charged to a predetermined capacitance by a voltage applied by a power supply voltage source. A first transistor Q1 connected to provide a high current; And And a current source 500 for providing a constant current to the base electrode and the emitter electrode of the first transistor Q1 so as to keep the first transistor Q1 always in an operating state. Circuit. The capacitor capacitance increasing circuit of claim 1, wherein the first transistor (Q1) is an NPN transistor. 2. The base electrode of claim 1, wherein the current source 500 is connected between one end of the capacitor C and a contact of a base electrode of the first transistor Q1 and the power supply voltage source. A first constant current source 502 for supplying a constant current to the; A second transistor (Q2) having a collector electrode connected to an emitter electrode of the first transistor (Q1) and an emitter electrode connected to the power supply voltage source; And A second source for supplying a current equal to the current supplied to the base electrode of the first transistor Q1 to the base electrode of the second transistor Q2 to control a current flowing through the collector electrode of the second transistor Q2. A capacitor capacity increasing circuit comprising two constant current sources (504). 4. The capacitor capacitance increasing circuit of claim 3 wherein the second transistor (Q2) is an NPN transistor. 2. The β of claim 1, wherein the high current is a collector current of the first transistor. , Where Is the base current of the first transistor and β is the current gain of the first transistor. 2. The capacitor capacitance increasing circuit of claim 1 wherein the high capacitance capacitor has a capacitance of βC, wherein β is a current gain of the first transistor and C is a capacitance of the capacitor.