CN102420578B - On-chip low pass filter - Google Patents
On-chip low pass filter Download PDFInfo
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- CN102420578B CN102420578B CN201010298491.4A CN201010298491A CN102420578B CN 102420578 B CN102420578 B CN 102420578B CN 201010298491 A CN201010298491 A CN 201010298491A CN 102420578 B CN102420578 B CN 102420578B
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- 239000004065 semiconductor Substances 0.000 claims abstract description 177
- 239000003990 capacitor Substances 0.000 claims abstract description 52
- 238000001914 filtration Methods 0.000 abstract description 15
- 230000003071 parasitic effect Effects 0.000 abstract description 7
- 229910044991 metal oxide Inorganic materials 0.000 abstract 1
- 150000004706 metal oxides Chemical class 0.000 abstract 1
- 238000010586 diagram Methods 0.000 description 6
- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- IXSZQYVWNJNRAL-UHFFFAOYSA-N etoxazole Chemical compound CCOC1=CC(C(C)(C)C)=CC=C1C1N=C(C=2C(=CC=CC=2F)F)OC1 IXSZQYVWNJNRAL-UHFFFAOYSA-N 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
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Abstract
The invention discloses an on-chip low pass filter consisting of four P-channel MOS (Metal Oxide Semiconductor) transistors, two capacitors and a current source. On the basis of the traditional on-chip low pass filter, an outside control circuit for starting a circuit is removed, and an MOS transistor and a capacitor are additionally provided to form another low pass filtering unit for carrying out low pass filtering on high input noise of the whole circuit so as to prevent the high input noise from being fed forward to output by a parasitic capacitor of the MOS transistor and improve a filtering performance of the on-chip low pass filter. The low pass filtering unit further forms a fast start-up circuit with the current source, thus a complex control circuit in the prior art is saved, the cost can be effectively saved, and the design area can be reduced.
Description
Technical field
The present invention relates to low pass filter design technical field, relate in particular to low pass filter on a kind of sheet.
Background technology
On sheet, low pass filter is the vitals of low noise linear voltage regulator, and on sheet, the filtering performance of low pass filter is directly connected to the service behaviour of low noise linear voltage regulator.In the design of low noise linear voltage regulator, the design of low pass filter on sheet, requires to have extremely low cut-off frequency, is generally 1Hz left and right.In addition, owing to will considering the problem of design area, therefore circuit is also succinctly one of the major issue that will consider in design.
As shown in Figure 1, be the circuit theory diagrams of low pass filter on the sheet of prior art.Wherein metal-oxide-semiconductor M1 is the resistive element of this filter, and capacitor C1 is the capacity cell of this filter, and metal-oxide-semiconductor M2 provides bias voltage for metal-oxide-semiconductor M1; Capacitor C2 is the grid of metal-oxide-semiconductor M1 and the parasitic capacitance of drain electrode; Metal-oxide-semiconductor M3, current source I1 and control circuit form start-up circuit jointly.
But applicant studies discovery, on the sheet of prior art at least there is following defect in the design of low pass filter:
Due to the high pass effect of the grid of M1 and the parasitic capacitance C2 of drain electrode, the radio-frequency component of input signal is applied to output above by grid and the capacitor C2 of metal-oxide-semiconductor M2, has therefore reduced the ability of filtering high-frequency signal; Meanwhile, because the start-up circuit of existing scheme comprises metal-oxide-semiconductor M3, current source I1 and control circuit, therefore complex structure, is unfavorable for reducing design cost and dwindles design area.
Summary of the invention
In view of this, the invention provides low pass filter on a kind of sheet, the ability of the filtering high-frequency signal existing with low pass filter on solving existing is poor, and baroque problem, and technical scheme is as follows:
Low pass filter on a kind of sheet, comprising:
Four P channel MOS tubes, are respectively the first metal-oxide-semiconductor, the second metal-oxide-semiconductor, the 3rd metal-oxide-semiconductor and the 4th metal-oxide-semiconductor; Two capacitors, are respectively the first capacitor and the second capacitor; A current source; Wherein:
Described the first metal-oxide-semiconductor is connected signal input part with the source electrode of the second metal-oxide-semiconductor; The drain electrode of described the first metal-oxide-semiconductor is connected signal output part with one end of the first capacitor; The grid of described the first metal-oxide-semiconductor connects the drain electrode of the 3rd metal-oxide-semiconductor and one end of the second capacitor; The drain electrode of described the second metal-oxide-semiconductor connects the source electrode of the 4th metal-oxide-semiconductor; The source electrode of described the 3rd metal-oxide-semiconductor connects the grid of the second metal-oxide-semiconductor, and is jointly connected on the connecting line of the drain electrode of the second metal-oxide-semiconductor and the source electrode of the 4th metal-oxide-semiconductor with the grid of the second metal-oxide-semiconductor; Described the 4th drain electrode of metal-oxide-semiconductor and the negative pole of current source are connected; The grid of described the 3rd metal-oxide-semiconductor connects the grid of the 4th metal-oxide-semiconductor, and is jointly connected on the drain electrode of the 4th metal-oxide-semiconductor and the connecting line of current source negative pole with the grid of the 4th metal-oxide-semiconductor; The other end, the other end of the second capacitor and the positive pole of current source of described the first capacitor all with reference to be connected.
Preferably, in above-mentioned upper low pass filter, the width of described the first metal-oxide-semiconductor grid is less than the length of the first metal-oxide-semiconductor grid, and the width of the second metal-oxide-semiconductor grid is greater than the length of the second metal-oxide-semiconductor grid, and the width of the second metal-oxide-semiconductor grid is much larger than the width of the first metal-oxide-semiconductor grid.
Preferably, in above-mentioned upper low pass filter, the width of described the 3rd metal-oxide-semiconductor grid is less than the length of the 3rd metal-oxide-semiconductor grid, and the width of the 4th metal-oxide-semiconductor grid is greater than the length of the 4th metal-oxide-semiconductor grid, and the width of the 4th metal-oxide-semiconductor grid is much larger than the width of the 3rd metal-oxide-semiconductor grid.
Preferably, in above-mentioned upper low pass filter, described the first capacitor and the second capacitor are replaced by N-channel MOS pipe the 5th metal-oxide-semiconductor and the 6th metal-oxide-semiconductor with larger specific capacitance respectively.
Preferably, in above-mentioned upper low pass filter, the order of magnitude of described current source is 1uA, and the order of magnitude of described the first capacitor is a hundreds of pF.
Preferably, in above-mentioned upper low pass filter, described current source is DC current source.
As can be seen from the above technical solutions, on the basis of the present invention's low pass filter on existing, remove the external control circuit of circuit start, a metal-oxide-semiconductor and capacitor are increased, common another low-pass filter unit of formation, input strong noise to whole circuit is carried out low-pass filtering, thereby has avoided input strong noise to be fed forward to output by the parasitic capacitance of metal-oxide-semiconductor, has improved the filtering performance of low pass filter on sheet; This low-pass filter unit also formed fast start circuit together with current source, thereby saved control circuit complicated in prior art, can be effectively cost-saving with dwindle design area.
Brief description of the drawings
In order to be illustrated more clearly in the embodiment of the present invention or technical scheme of the prior art, to the accompanying drawing of required use in embodiment or description of the Prior Art be briefly described below, apparently, accompanying drawing in the following describes is only some embodiments of the present invention, for those of ordinary skill in the art, do not paying under the prerequisite of creative work, can also obtain according to these accompanying drawings other accompanying drawing.
The circuit theory schematic diagram of low pass filter on the sheet that Fig. 1 provides for prior art;
The circuit theory schematic diagram of a kind of upper low pass filter that Fig. 2 provides for the embodiment of the present invention;
The circuit theory schematic diagram of low pass filter on the another kind of sheet that Fig. 3 provides for the embodiment of the present invention.
Embodiment
On the basis of embodiment of the present invention low pass filter on existing, remove the external control circuit of circuit start, a metal-oxide-semiconductor and capacitor are increased, common another low-pass filter unit of formation, input strong noise to whole circuit is carried out low-pass filtering, thereby avoid input strong noise to be fed forward to output by the parasitic capacitance of metal-oxide-semiconductor, improved the filtering performance of low pass filter on sheet; This low-pass filter unit also formed fast start circuit together with current source, thereby saved control circuit complicated in prior art, can be effectively cost-saving with dwindle design area.
In order to make those skilled in the art better understand and implement the present invention, below with reference to Figure of description, the specific embodiment of the present invention is described in further detail.
As shown in Figure 2, on the sheet that the embodiment of the present invention provides, low pass filter can comprise:
Four P channel MOS tubes, are respectively the first metal-oxide-semiconductor (M1), the second metal-oxide-semiconductor (M2), the 3rd metal-oxide-semiconductor (M3) and the 4th metal-oxide-semiconductor (M4); Two capacitors, are respectively the first capacitor (C1) and the second capacitor (C3); A current source (I1); Wherein:
Described the first metal-oxide-semiconductor (M1) is connected signal input part with the source electrode of the second metal-oxide-semiconductor (M2); The drain electrode of described the first metal-oxide-semiconductor (M1) is connected signal output part with one end of the first capacitor (C1); The grid of described the first metal-oxide-semiconductor (M1) connects the drain electrode of the 3rd metal-oxide-semiconductor (M3) and one end of the second capacitor (C3); The drain electrode of described the second metal-oxide-semiconductor (M2) connects the source electrode of the 4th metal-oxide-semiconductor (M4); The source electrode of described the 3rd metal-oxide-semiconductor (M3) connects the grid of the second metal-oxide-semiconductor (M2), and is jointly connected on the connecting line of the drain electrode of the second metal-oxide-semiconductor (M2) and the source electrode of the 4th metal-oxide-semiconductor (M4) with the grid of the second metal-oxide-semiconductor (M2); The drain electrode of described the 4th metal-oxide-semiconductor (M4) is connected with the negative pole of current source (I1); The grid of described the 3rd metal-oxide-semiconductor (M3) connects the grid of the 4th metal-oxide-semiconductor (M4), and is jointly connected on the drain electrode of the 4th metal-oxide-semiconductor (M4) and the connecting line of current source (I1) negative pole with the grid of the 4th metal-oxide-semiconductor (M4); The positive pole of the other end of described the first capacitor (C1), the other end of the second capacitor (C3) and current source (I1) all with reference to (GND) be connected.
On sheet shown in Fig. 2, in the circuit theory diagrams of low pass filter, comprise two low-pass filter units, for convenience of description, become respectively the first low-pass filter unit and the second low-pass filter unit.In the first low-pass filter unit, the first metal-oxide-semiconductor (M1) and the second metal-oxide-semiconductor (M2) provide the resistive element of low-pass filter unit jointly, the 4th metal-oxide-semiconductor (M4) is that the first metal-oxide-semiconductor (M1) and the second metal-oxide-semiconductor (M2) provide bias voltage, and the first capacitor (C1) provides the capacity cell of low-pass filter unit; In the second low-pass filter unit, the 3rd metal-oxide-semiconductor (M3) provides the resistive element of low-pass filter unit, the 4th metal-oxide-semiconductor (M4) is that the 3rd metal-oxide-semiconductor (M3) provides bias voltage, and the second capacitor (C3) provides the capacity cell of low-pass filter unit.The second low pass filter carries out low-pass filtering to the grid voltage of the first metal-oxide-semiconductor (M1) in the first low-pass filter unit, thereby avoid input strong noise to be fed forward to output by the grid of the first metal-oxide-semiconductor (M1) and the parasitic capacitance of drain electrode, improved the filtering performance of low pass filter on sheet.
On sheet shown in Fig. 2, in the circuit theory diagrams of low pass filter, start-up circuit part is made up of jointly a current source (I1) and the second low-pass filter unit.When circuit start; the 4th metal-oxide-semiconductor (M4) is that the 3rd metal-oxide-semiconductor (M3) provides bias voltage; now; because the resistance of the 3rd metal-oxide-semiconductor (M3) is very large; therefore the voltage on the second capacitor (C3) starts to raise very slowly; in elevation process; because the source voltage of the first metal-oxide-semiconductor (M1) equals input voltage; therefore the first metal-oxide-semiconductor (M1) is opened completely; electric charge is given the first capacitor (C1) quick charge by the first metal-oxide-semiconductor (M1), thereby realizes the quick startup of whole upper low pass filter.The start-up circuit of low pass filter on the sheet that the embodiment of the present invention provides, because without additional control circuit, therefore simple in structure, can be effectively cost-saving and dwindle design area.
On provided by the invention in low pass filter embodiment, in above-described embodiment, the width of described the first metal-oxide-semiconductor (M1) grid is less than the length of the first metal-oxide-semiconductor (M1) grid, the width of the second metal-oxide-semiconductor (M2) grid is greater than the length of the second metal-oxide-semiconductor (M2) grid, and the width of the second metal-oxide-semiconductor (M2) grid is much larger than the width of the first metal-oxide-semiconductor (M1) grid.
The object of design is the resistance in order to increase by the first low-pass filter unit like this, and in practical application, the resistance that can form is at the order of magnitude of several Gohm.
On provided by the invention in low pass filter embodiment, in above-described embodiment, the width of described the 3rd metal-oxide-semiconductor (M3) grid is less than the length of the 3rd metal-oxide-semiconductor (M3) grid, the width of the 4th metal-oxide-semiconductor (M4) grid is greater than the length of the 4th metal-oxide-semiconductor (M4) grid, and the width of the 4th metal-oxide-semiconductor (M4) grid is much larger than the width of the 3rd metal-oxide-semiconductor (M3) grid.
The object of design is the resistance in order to increase by the second low-pass filter unit like this, and in practical application, the resistance that can form is also at the order of magnitude of several Gohm.
On provided by the invention, in low pass filter embodiment, in above-described embodiment, the order of magnitude of described current source (I1) is 1uA, and is DC power supply; The order of magnitude of described the first capacitor (C1) is a hundreds of pF.
In the application of low noise linear voltage regulator, the designing requirement of low pass filter will reach the cut-off frequency of about 1-10Hz, and because the leakage current of device exists, on general sheet, resistance maximum can only be accomplished several Gohm.Therefore, according to the principle of RC low pass filter, the order of magnitude of the first capacitor (C1) is a hundreds of pF, and for example, when cut-off frequency equals 1Hz, when resistance equals 2Gohm, the first capacitor (C1) is 500pF.
By the scheme that the embodiment of the present invention is provided, specifically set forth in conjunction with the design parameter in practical application below.
As shown in Figure 2:
The source electrode of the first metal-oxide-semiconductor (M1) connects signal input part, and drain electrode connects signal output part.Wherein, the width W 1 of the first metal-oxide-semiconductor (M1) grid is less than the length L 1 of the first metal-oxide-semiconductor (M1) grid, for the first low-pass filter unit provides resistive element, by designing the first metal-oxide-semiconductor (M1) grid breadth length ratio, and the ratio of first metal-oxide-semiconductor (M1) grid width W1 and the second metal-oxide-semiconductor (M2) grid width W2, can form the resistance of several Gohm orders of magnitude.In this example, the size of the first metal-oxide-semiconductor (M1) is as follows: W1=0.8um, L1=10um.
The source electrode of the second metal-oxide-semiconductor (M2) connects signal input part, and the grid of the second metal-oxide-semiconductor (M2) connects its drain electrode, connects the source electrode of the 3rd metal-oxide-semiconductor (M3) simultaneously.The width W 2 that the length L 2 of the second metal-oxide-semiconductor (M2) grid equals length L 1, the second metal-oxide-semiconductor (M2) grid of the first metal-oxide-semiconductor (M1) grid is 100 times of the first metal-oxide-semiconductor (M1) grid width W1; In this example, the size of the second metal-oxide-semiconductor (M2) is as follows: W2=80um, L2=10um.
The source electrode of the 3rd metal-oxide-semiconductor (M3) connects the grid of the second metal-oxide-semiconductor (M2), the drain electrode of the 3rd metal-oxide-semiconductor (M3) connects the grid of the first metal-oxide-semiconductor (M1), and the grid of the 3rd metal-oxide-semiconductor (M3) connects the grid of the 4th metal-oxide-semiconductor (M4).In this example, the size of the 3rd metal-oxide-semiconductor (M3) is identical with the first metal-oxide-semiconductor (M1), i.e. W3=0.8um, L3=10um.
The source electrode of the 4th metal-oxide-semiconductor (M4) connects the drain electrode of the second metal-oxide-semiconductor (M2), the drain electrode of the 4th metal-oxide-semiconductor (M4) connects the grid of the 4th metal-oxide-semiconductor (M4), and the grid of the 4th metal-oxide-semiconductor (M4) connects the negative pole of current source (I1) and the grid of the 3rd metal-oxide-semiconductor (M3).The width W 4 of the 4th metal-oxide-semiconductor (M4) grid is greater than the length L 4 of the 4th metal-oxide-semiconductor (M4) grid, and the width of the 4th metal-oxide-semiconductor (M4) grid is much larger than the width of the 3rd metal-oxide-semiconductor (M3) grid; In this example, the size of the 4th metal-oxide-semiconductor (M4) is identical with the first metal-oxide-semiconductor (M1), i.e. W4=80um, L4=10um.
The negative pole of current source (I1) connects the drain electrode of the 4th metal-oxide-semiconductor (M4), and positive pole connects reference (GND), and the electric current of about 1uA is provided.
The signal output part of the first capacitor (C1) termination low pass filter, another termination is with reference to ground (GND); The first capacitor (C1) provides the capacity cell of the first low-pass filter unit, and its size is approximately 200pF.
The grid of the second capacitor (C3) termination first metal-oxide-semiconductor (M1), another termination is with reference to ground (GND); The second capacitor (C3) provides the capacity cell of the second low-pass filter unit and the capacity cell of start-up circuit.
In above-described embodiment, the second low-pass filter unit that the 3rd metal-oxide-semiconductor (M3) and the second capacitor (C3) form, the grid voltage that is the first metal-oxide-semiconductor (M1) has carried out low-pass filtering, thereby avoid inputting high-frequency noise and be fed forward to output by the grid of the first metal-oxide-semiconductor (M1) and the parasitic capacitance of drain electrode, thereby improved the filtering performance of low pass filter on sheet; The second low-pass filter unit and current source (I1), the start-up circuit part of whole upper low pass filter is also provided, when startup, in voltage rising process on the second capacitor (C3), the first metal-oxide-semiconductor (M1) is opened completely, give the first capacitor (C1) quick charge, realize fast and starting, thereby saved control circuit complicated in prior art, can be effectively cost-saving with dwindle design area.
As shown in Figure 3, in one embodiment of the invention, capacity cell the first capacitor (C1) and the second capacitor (C3) can be realized by the metal-oxide-semiconductor with larger specific capacitance, N-channel MOS pipe the 5th metal-oxide-semiconductor (M5) and the 6th metal-oxide-semiconductor (M6) as shown in FIG..
The object of design is further to reduce design area like this.Because metal-oxide-semiconductor device is compared in capacitor element, shared design area is larger, if therefore adopt the metal-oxide-semiconductor with larger specific capacitance to replace capacity cell, can not increase on the basis of complexity in circuits as far as possible, the design area of low pass filter on sheet is further reduced.
The foregoing is only preferred embodiment of the present invention, be not limited to the present invention, within the spirit and principles in the present invention all, any amendment of making, be equal to replacement, improvement etc., within all should being included in protection scope of the present invention.
Claims (4)
1. a low pass filter on sheet, is characterized in that, comprising:
Four P channel MOS tubes, are respectively the first metal-oxide-semiconductor (M1), the second metal-oxide-semiconductor (M2), the 3rd metal-oxide-semiconductor (M3) and the 4th metal-oxide-semiconductor (M4); Two capacitors, are respectively the first capacitor (C1) and the second capacitor (C3); A current source (I1); Wherein:
Described the first metal-oxide-semiconductor (M1) is connected signal input part with the source electrode of the second metal-oxide-semiconductor (M2); The drain electrode of described the first metal-oxide-semiconductor (M1) is connected signal output part with one end of the first capacitor (C1); The grid of described the first metal-oxide-semiconductor (M1) connects the drain electrode of the 3rd metal-oxide-semiconductor (M3) and one end of the second capacitor (C3); The drain electrode of described the second metal-oxide-semiconductor (M2) connects the source electrode of the 4th metal-oxide-semiconductor (M4); The source electrode of described the 3rd metal-oxide-semiconductor (M3) connects the grid of the second metal-oxide-semiconductor (M2), and is jointly connected on the connecting line of the drain electrode of the second metal-oxide-semiconductor (M2) and the source electrode of the 4th metal-oxide-semiconductor (M4) with the grid of the second metal-oxide-semiconductor (M2); The drain electrode of described the 4th metal-oxide-semiconductor (M4) is connected with the negative pole of current source (I1); The grid of described the 3rd metal-oxide-semiconductor (M3) connects the grid of the 4th metal-oxide-semiconductor (M4), and is jointly connected on the drain electrode of the 4th metal-oxide-semiconductor (M4) and the connecting line of current source (I1) negative pole with the grid of the 4th metal-oxide-semiconductor (M4); The positive pole of the other end of described the first capacitor (C1), the other end of the second capacitor (C3) and current source (I1) all with reference to (GND) be connected;
The width of described the first metal-oxide-semiconductor (M1) grid is less than the length of the first metal-oxide-semiconductor (M1) grid, the width of the second metal-oxide-semiconductor (M2) grid is greater than the length of the second metal-oxide-semiconductor (M2) grid, and the width of the second metal-oxide-semiconductor (M2) grid is much larger than the width of the first metal-oxide-semiconductor (M1) grid;
The width of described the 3rd metal-oxide-semiconductor (M3) grid is less than the length of the 3rd metal-oxide-semiconductor (M3) grid, the width of the 4th metal-oxide-semiconductor (M4) grid is greater than the length of the 4th metal-oxide-semiconductor (M4) grid, and the width of the 4th metal-oxide-semiconductor (M4) grid is much larger than the width of the 3rd metal-oxide-semiconductor (M3) grid.
2. according to claim 1 upper low pass filter, is characterized in that, described the first capacitor (C1) and the second capacitor (C3) are replaced by N-channel MOS pipe the 5th metal-oxide-semiconductor (M5) and the 6th metal-oxide-semiconductor (M6) with larger specific capacitance respectively.
3. according to claim 1 upper low pass filter, is characterized in that, the order of magnitude of described current source (I1) is 1uA, and the order of magnitude of described the first capacitor (C1) is a hundreds of pF.
4. according to claim 2 upper low pass filter, is characterized in that, described current source (I1) is DC current source.
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Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1219029A (en) * | 1997-11-21 | 1999-06-09 | 国际商业机器公司 | Integrated resistor in use of continuous time signal processing |
| US6084470A (en) * | 1997-11-28 | 2000-07-04 | Kabushiki Kaisha Toshiba | Filter circuit capable of setting various filter characteristics |
| CN101777880A (en) * | 2010-01-19 | 2010-07-14 | 北京大学 | Band-pass filter |
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| JP2918650B2 (en) * | 1990-07-26 | 1999-07-12 | バブコツク日立株式会社 | Boiler plant automatic control device and control method |
| JPH09284001A (en) * | 1996-04-15 | 1997-10-31 | Nec Corp | Pulse output circuit |
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Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1219029A (en) * | 1997-11-21 | 1999-06-09 | 国际商业机器公司 | Integrated resistor in use of continuous time signal processing |
| US6084470A (en) * | 1997-11-28 | 2000-07-04 | Kabushiki Kaisha Toshiba | Filter circuit capable of setting various filter characteristics |
| CN101777880A (en) * | 2010-01-19 | 2010-07-14 | 北京大学 | Band-pass filter |
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