CN209913792U - High-pass filter - Google Patents

Abstract

The embodiment of the utility model discloses a high pass filter, it is through electric connection's condenser, bias circuit, bipolar transistor circuit and load circuit in proper order, under the bias voltage that the bias circuit provided, filter input signal and can adjust the cut-off frequency of this wave filter through the current gain that changes self through the bipolar transistor circuit; the output resistance of the bipolar transistor is utilized to ensure that the silicon chip area occupied by the high-pass filter in the semiconductor chip is very small, and simultaneously, the input resistance of the bipolar transistor circuit is easy to control and is not easy to be interfered by the outside, so that the high-pass filter has the frequency characteristic of lower cut-off frequency and can also adjust the cut-off frequency of the filter randomly; thereby realizing the integrated application of the high-frequency filter in the semiconductor chip.

Description

High-pass filter

Technical Field

The utility model relates to an electronic circuit semiconductor technology field especially relates to a high pass filter.

Background

At present, in an integrated circuit analog electronic circuit, a CMOS process is mostly adopted for the design of a filter, and particularly, a plurality of designers in a transmission system of a plurality of analog receiving circuits and optical sensing receiving circuits adopt the CMOS process because the circuits are simple, but the stability and consistency of the CMOS process are not good, so that the CMOS process has certain use limitation, namely if a more complex circuit needs to be added to ensure the stability, the cut-off frequency of another important parameter of the filter needs to be more stable and consistent, and in the design of the CMOS process, the gain change of the CMOS process is large, so that the stability and consistency of the cut-off frequency are difficult to guarantee; meanwhile, designers also select an R \ C \ L mode in the early stage of the integrated circuit, the realization result is very direct, an equivalent circuit is not needed, the stability and consistency of cut-off frequency are good, but in the requirements of certain filters, a larger RCL is possibly needed, so that the RCL occupies a larger area of a silicon chip in the design of the integrated circuit.

That is, in the related art scheme of the filter design circuit, there are disadvantages that the chip size of the integrated circuit also increases due to the large resistor and the large capacitor, and the stability and consistency of the cut-off frequency are difficult to be secured.

SUMMERY OF THE UTILITY MODEL

The embodiment of the application provides a high-pass filter, which is simple in circuit, good in stability and consistency, small in silicon chip area and capable of setting cut-off frequency at will.

The high-pass filter is characterized by comprising a filter capacitor, a bias circuit and a bipolar transistor circuit which are electrically connected in sequence, wherein the filter capacitor is used for filtering an input signal, the bias circuit is used for providing bias current for the bipolar transistor circuit, and the bipolar transistor circuit is used for adjusting the cut-off frequency of the filter by changing the current gain of the bipolar transistor circuit under the action of the bias circuit.

Optionally, in one embodiment, the bipolar transistor circuit includes an NPN transistor or a PNP transistor.

Optionally, in one embodiment, the bias circuit includes a current mirror circuit, and the current mirror circuit includes a constant current source circuit, a transistor control circuit, and a mirror current source circuit, which are electrically connected in sequence, where the constant current source circuit is configured to provide a reference current for the mirror current source circuit, the transistor control circuit is configured to adjust an output current of the mirror current source circuit, and the mirror current source circuit is configured to output a bias current of the bipolar transistor circuit under the control of the transistor control circuit.

Alternatively, in one of the embodiments, the bias circuit may be replaced by a resistor or a bias circuit structure composed of a resistor element and a transistor element.

Optionally, in one embodiment, if the bipolar transistor circuit includes an NPN transistor, the mirror current source circuit includes a bipolar basic current mirror composed of two PNP transistors; if the bipolar transistor circuit comprises a PNP transistor, the mirror current source circuit comprises a bipolar basic current mirror consisting of two NPN transistors.

Optionally, in one embodiment, if the mirror current source circuit includes a bipolar basic current mirror composed of two PNP transistors, the transistor control circuit includes an NPN transistor; and if the mirror current source circuit comprises a bipolar basic current mirror consisting of two NPN transistors, the transistor control circuit comprises a PNP transistor.

Optionally, in one embodiment, the high-pass filter further includes the load circuit.

Optionally, in one embodiment, the load circuit includes a load resistor.

Optionally, in one embodiment, the load circuit includes a diode circuit.

Implement the embodiment of the utility model provides a, will have following beneficial effect:

the high-pass filter is a high-pass filter circuit formed by utilizing the output resistance of a bipolar transistor, and filters an input signal under the bias current provided by a bias circuit through a capacitor, the bias circuit, the bipolar transistor circuit and a load circuit which are electrically connected in sequence, and the cut-off frequency of the filter can be adjusted by changing the current gain of the bipolar transistor circuit through the bipolar transistor circuit; the output resistance of the bipolar transistor is utilized to ensure that the silicon chip area occupied by the high-pass filter in the semiconductor chip is very small, and simultaneously, the input resistance of the bipolar transistor circuit is easy to control and is not easy to be interfered by the outside, so that the high-pass filter has the frequency characteristic of lower cut-off frequency and can also adjust the cut-off frequency of the filter randomly; the integrated application of the high-frequency filter in the semiconductor chip is easily realized.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

Wherein:

FIG. 1 is a block diagram of a high pass filter in one embodiment;

FIG. 2 is a circuit schematic of a high pass filter in one embodiment;

FIG. 3 is a circuit schematic of a high pass filter in another embodiment;

fig. 4 is an equivalent circuit diagram of the high-pass filter shown in fig. 2 and 3.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the description of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. It will be understood that, as used herein, the terms "first," "second," and the like may be used herein to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish one element from another.

The high-pass filter circuit is formed by using the output resistance of the transistor in order to overcome the defect that the chip size of an integrated circuit is increased along with the increase of a large resistor and a large capacitor, so that the high-pass filter circuit is different from the traditional high-pass filter circuit, an effective high-pass filter circuit can be designed in a chip, meanwhile, a small silicon area can be occupied, in addition, the high-pass filter circuit occupies an area which is smaller than several times to several hundred times than a common resistor element in the design of the high-pass filter, the characteristic change is small along with the change of the type of the transistor, and the reliability of the high-pass filter circuit can be improved. And the cut-off frequency of the filter can be adjusted arbitrarily. As shown in fig. 1, a block diagram of a high pass filter in an embodiment includes a filter capacitor 110, a bias circuit 120, a bipolar transistor circuit 130, and a load circuit 140, which are electrically connected in sequence.

Wherein the filter capacitor 110 is used to filter the input signal.

The bias circuit 120 is configured to provide a bias current for the bipolar transistor circuit 130, the bias circuit 120 includes a current mirror circuit, the current mirror circuit includes a constant current source circuit, a transistor control circuit, and a mirror current source circuit, which are electrically connected in sequence, a reference current of the current mirror circuit is provided by the constant current source circuit, the mirror current source circuit outputs the bias current of the bipolar transistor circuit under the control of the transistor control circuit, and the output current of the mirror current source circuit is adjusted by the transistor control circuit. Further, the bias current provided to the bipolar transistor circuit 130 does not need to be a current mirror circuit, and the bias circuit 120 may also be a bias circuit formed by a resistor, which is directly connected in series with the bipolar transistor circuit 130 to provide the bias current to the bipolar transistor circuit 130; the bias circuit 120 may also be a bias circuit structure composed of a resistor element and a transistor element to provide a bias current for the bipolar transistor circuit 130; the configuration of the bias circuit may be used in this application or may replace the current mirror circuit mentioned in this application by any general standard bias circuit, which is not specifically limited in this example.

The bipolar transistor circuit 130 is used for adjusting the cut-off frequency of the filter by changing the current gain of the bipolar transistor circuit under the action of the bias circuit 120, and the bipolar transistor circuit comprises an NPN transistor or a PNP transistor; therefore, the filter circuit adopts the bipolar transistor instead of the COMS or other technologies, and mainly considers that the input resistance of the bipolar transistor is easy to control and is not easy to be interfered by the outside; and when the bipolar transistor is biased and works in a dynamic range, the output resistance of the bipolar transistor is larger, so that the output resistance of the bipolar transistor can be utilized to ensure that the silicon chip area occupied by the filter circuit in a semiconductor chip is small, and the integration of the high-frequency filter in the semiconductor chip is convenient to realize. Further, if the bipolar transistor circuit comprises an NPN transistor, the mirror current source circuit comprises a bipolar basic current mirror composed of two PNP transistors, and the transistor control circuit comprises an NPN transistor; if the bipolar transistor circuit comprises a PNP transistor, the mirror current source circuit comprises a bipolar basic current mirror consisting of two NPN transistors, and the transistor control circuit comprises a PNP transistor. Further, for higher precision and achieving a certain output capability, the transistors in the transistor control circuit use bipolar transistors or even triode transistors with stacked configuration to increase the output resistance of the transistors, such as 3D stacked transistors.

The load circuit 140 includes one of a load resistor and a diode circuit.

In one embodiment, as shown in fig. 2, a circuit diagram of a high-pass filter is shown, the high-pass filter includes a filter capacitor C, NPN, a transistor Q1, a bipolar basic mirror current mirror structure composed of two PNP transistors Q3 and Q4, a constant current source Ie, an NPN transistor Q2, and a load resistor R1; the constant current source Ie provides a reference current, the PNP transistor Q4 in the bipolar basic mirror current mirror structure is a diode connection structure, the base and the collector of the PNP transistor Q4 are connected with each other, the current mirror structure provides a bias circuit for the NPN transistor Q1, the mirror current of the bipolar basic mirror current mirror structure is output by the PNP transistor Q3, the magnitude of the output current is controlled by the NPN transistor Q2, the input of the high-pass filter is connected to the base of the input NPN transistor Q1 through the filter capacitor C, and the output of the high-pass filter is led out from a node where the emitter of the NPN transistor Q1 and the load resistor R1 are connected with each other. The filtering principle of the high-pass filter is as follows: assuming that the output resistance of the PNP transistor Q3 itself is R0 and the current gain of the NPN transistor Q1 is β, the total resistance seen at the base of the Q1 of the circuit is the parallel value of R0 and (β × R1). Therefore, the transfer function of the circuit is expressed by the following equation (1),

wherein Rp is the parallel resistance of R0 and (beta R1), and is

The cutoff frequency F of the circuit is expressed by the following equation (2):

from the above equation, if R0 can be a sufficiently large value, since the load resistor R1 is a value multiplied by the current gain β of the NPN transistor Q1, it is also a sufficiently large value, and the value of Rp is also a sufficiently large value; meanwhile, the value of the current gain beta can be adjusted, so that the value of Rp can be adjusted, namely the cut-off frequency F can be adjusted; and the cut-off frequency of the high-pass filter can be adjusted by R1 or current gain β. In this way, a high pass filter with the desired cut-off frequency value can be designed. In addition, R1 as a resistance element may be replaced with a diode; the circuit for providing the NPN transistor Q1 with an appropriate bias does not necessarily need to be a current mirror circuit. For example, if the requirement is not so high and the resistance value is not so large, the bias circuit may be formed by connecting only resistor elements in series in the circuit, or may be formed by a combination of resistor elements and transistor elements; the resistor can be directly connected in series to replace the PNP transistor Q3, and the structure of the PNP transistor Q4 can be used as a bias circuit; the bias circuit can be configured to be used in the current mirror structure of this example or in place of the current mirror structure by any general standard bias circuit, but the current mirror structure has high stability.

In another embodiment, as shown in fig. 3, a circuit diagram of a high-pass filter of another embodiment is shown, the high-pass filter includes a filter capacitor C, PNP, a transistor Q1, a bipolar basic mirror current mirror structure composed of two NPN transistors Q3 and Q4, a constant current source Ie, a PNP transistor Q2, and a load resistor R1, and the circuit is a circuit forming a complementary relationship with the circuit of fig. 3; the constant current source Ie provides a reference current, the NPN transistor Q4 in the bipolar basic mirror current mirror structure is a diode connection structure, the base and collector of which are connected to each other, the current mirror structure provides a bias circuit for the PNP transistor Q1, the mirror current of the bipolar basic mirror current mirror structure is output by the NPN transistor Q3, the magnitude of the output current is controlled by the PNP transistor Q2, the input of the high pass filter is connected to the base of the input PNP transistor Q1 through the filter capacitor C, the load element and the constant current circuit Ie are connected to a power supply voltage, and the output of the high pass filter is led out from a node where the emitter of the PNP transistor Q1 and the load resistor R1 are connected to each other. The filtering principle of the high-pass filter is as follows: assuming that the output resistance of the PNP transistor Q3 itself is R0 and the current gain of the PNP transistor Q1 is β, the total resistance seen at the base of Q1 of the circuit is the parallel value of R0 and (β × R1). Therefore, the transfer function and the cut-off frequency of the circuit are expressed by the following equations (3) and (4),

wherein, R0 is the output resistance of PNP transistor Q1, β is the current gain of PNP transistor Q1, R1 is the load resistance connected to the emitter of Q1, Rn is the parallel resistance of R0 and (β × R1), and isFrom the above equation, if R0 can be a sufficiently large value, the load resistor R1 is a sufficiently large value multiplied by the current gain β of the PNP transistor Q1, and the value of Rn is also sufficiently large; meanwhile, the value of the current gain beta can be adjusted, so that the value of Rn can be adjusted, namely the cut-off frequency F can be adjusted; and the cut-off frequency of the high-pass filter can be adjusted by R1 or current gain β. In this way, a high pass filter with the desired cut-off frequency value can be designed. In addition, R1 as a resistance element may be replaced with a diode; the circuit that provides the PNP transistor Q1 with the appropriate bias need not necessarily be a current mirror circuit. For example, such a bias circuit may be formed by only a resistor element, and may be formed by a combination of a resistor element and a transistor element. The configuration of the bias circuit can be used in the current mirror structure of this example or in place of the current mirror structure by any general standard bias circuit, and the transistor in the transistor control circuit uses a bipolar transistor or even a triode transistor having a stacked configuration to increase the output resistance of the transistor for higher accuracy and a certain output capability. As shown in fig. 4, it is a schematic diagram of an equivalent circuit of the high-pass filter of the two embodiments, the output terminal of the high-pass filter is represented by level conversion, the level conversion is represented by converting the NPN transistor Q1 or the PNP transistor Q1 into a corresponding equivalent circuit, and the voltage drop between the base and the emitter of the bipolar transistor Q1 is also represented by the equivalent circuit, that is, the high-pass filter is equivalent to an RC filter circuit.

The high-pass filter is a high-pass filter circuit formed by utilizing the output resistance of a bipolar transistor, and an input signal is filtered under the bias voltage provided by a bias circuit through a capacitor, the bias circuit, the bipolar transistor circuit and a load circuit which are electrically connected in sequence, and the cut-off frequency of the filter can be adjusted by changing the current gain of the bipolar transistor circuit; the output resistance of the bipolar transistor is utilized to make the high-pass filter smaller, so that the silicon chip area occupied in the semiconductor chip is smaller, and meanwhile, the input resistance of the bipolar transistor circuit is easier to control and is not easy to be interfered by the outside, so that the high-pass filter has the frequency characteristic of lower cut-off frequency, and the cut-off frequency of the filter can be adjusted at will; the integrated application of the high-frequency filter in the semiconductor chip is easily realized.

The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present application. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims (10)

1. The high-pass filter is characterized by comprising a filter capacitor, a bias circuit and a bipolar transistor circuit which are electrically connected in sequence, wherein the filter capacitor is used for filtering an input signal, the bias circuit is used for providing bias current for the bipolar transistor circuit, and the bipolar transistor circuit is used for adjusting the cut-off frequency of the filter by changing the current gain of the bipolar transistor circuit under the action of the bias circuit.

2. A high pass filter as claimed in claim 1, characterized in that the bipolar transistor circuit comprises an NPN transistor or a PNP transistor.

3. The high-pass filter according to claim 2, wherein the bias circuit comprises a current mirror circuit, the current mirror circuit comprises a constant current source circuit, a transistor control circuit and a mirror current source circuit, which are electrically connected in sequence, the constant current source circuit is used for providing a reference current for the mirror current source circuit, the transistor control circuit is used for adjusting an output current of the mirror current source circuit, and the mirror current source circuit is used for outputting a bias current of the bipolar transistor circuit under the control of the transistor control circuit.

4. A high pass filter according to claim 3, wherein if the bipolar transistor circuit comprises an NPN transistor, the mirrored current source circuit comprises a bipolar basic current mirror consisting of two PNP transistors; if the bipolar transistor circuit comprises a PNP transistor, the mirror current source circuit comprises a bipolar basic current mirror consisting of two NPN transistors.

5. The high pass filter according to claim 4, wherein if the mirrored current source circuit comprises a bipolar basic current mirror consisting of two PNP transistors, the transistor control circuit comprises an NPN transistor; and if the mirror current source circuit comprises a bipolar basic current mirror consisting of two NPN transistors, the transistor control circuit comprises a PNP transistor.

6. The high pass filter of claim 1, wherein the bias circuit comprises a resistor.

7. The high pass filter of claim 1, wherein the bias circuit comprises a bias circuit structure consisting of a resistor element and a transistor element.

8. The high pass filter of claim 1, further comprising a load circuit.

9. The high pass filter of claim 8, wherein the load circuit comprises a load resistor.

10. The high pass filter of claim 8, wherein the load circuit comprises a diode circuit.

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