CN110687950B - Source follower circuit and buffer circuit - Google Patents
Source follower circuit and buffer circuit Download PDFInfo
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- CN110687950B CN110687950B CN201810726169.3A CN201810726169A CN110687950B CN 110687950 B CN110687950 B CN 110687950B CN 201810726169 A CN201810726169 A CN 201810726169A CN 110687950 B CN110687950 B CN 110687950B
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- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
- G05F1/00—Automatic systems in which deviations of an electric quantity from one or more predetermined values are detected at the output of the system and fed back to a device within the system to restore the detected quantity to its predetermined value or values, i.e. retroactive systems
- G05F1/10—Regulating voltage or current
- G05F1/46—Regulating voltage or current wherein the variable actually regulated by the final control device is dc
- G05F1/56—Regulating voltage or current wherein the variable actually regulated by the final control device is dc using semiconductor devices in series with the load as final control devices
- G05F1/561—Voltage to current converters
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Abstract
Disclosed is a source follower circuit and a buffer circuit, including: the source follower circuit comprises a first current source, a first transistor and a second current source which are sequentially connected between a first power supply end and a second power supply end, wherein a control end of the first transistor receives an input voltage, and an intermediate node between the first transistor and the first current source is used for providing an output voltage.
Description
Technical Field
The invention relates to the field of integrated circuit design, in particular to a source follower circuit and a buffer circuit.
Background
The voltage follower is one of the most important modules in an analog circuit, and is widely applied to various analog circuit designs. The voltage follower is applied to the buffer circuit and the isolation circuit, transfers the waveform of the input signal to the output, and outputs sufficient current to drive the capacitive and resistive loads at the output point. It is therefore generally desirable in circuit design for the voltage follower to have a high linearity so that the output signal is as close as possible to the input signal.
Fig. 1 shows a circuit diagram of a conventional source follower, as shown in fig. 1, a gate of a transistor M1 receives an input voltage Vin, and a source thereof provides an output voltage Vout. The traditional source follower has the following defects: when the input voltage Vin changes, the voltage difference between the drain and the source of the transistor M1 and the voltage difference between the source and the substrate both change with the change of the input voltage Vin, and the body effect and the channel length modulation effect caused thereby affect the linearity of the source follower.
Fig. 2 shows a circuit schematic diagram of a conventional source follower, and as shown in fig. 2, the conventional art uses transistors M2 and M3 having different threshold voltages to constitute the source follower. The transistor M2 has a high threshold voltage, and the transistor M3 has a low threshold voltage. The difference between the threshold voltages of the transistors M2 and M3 is the source-drain voltage of the transistor M3. Since the difference between the threshold voltages of the transistors M2 and M3 does not change with the change of the input voltage Vin, the source-drain voltage of the transistor M3 also does not change with the change of the input voltage Vin, so the output impedance of the transistor M3 has a small influence on the low-frequency voltage, and the low-frequency voltage has a large gain.
Disclosure of Invention
In view of the above, an object of the present invention is to provide a source follower circuit and a buffer circuit including the source follower circuit, which further improve the linearity and the output dynamic range of the source follower.
According to an aspect of the invention, there is provided a source follower circuit comprising: the source follower circuit comprises a first current source, a first transistor and a second current source which are sequentially connected between a first power supply end and a second power supply end, wherein a control end of the first transistor receives an input voltage, and an intermediate node between the first transistor and the first current source is used for providing an output voltage.
Preferably, the clamping module includes a second transistor and a resistor connected in sequence between the first power supply terminal and the second pass terminal of the first transistor, wherein a control terminal of the second transistor is connected to an intermediate node of the first transistor and the first current source to receive the output voltage.
Preferably, when the output voltage is active, the second transistor is used to provide a current path of a constant current from the first power supply terminal to the first node.
Preferably, the first current source is configured to provide a first bias current, and the second current source is configured to provide a second bias current, wherein the constant current is a difference between the second bias current and the first bias current.
Preferably, the first transistor is a p-type channel field effect transistor, and the second transistor is an n-type channel field effect transistor.
Preferably, the first power supply terminal is configured to provide a power supply voltage, and the second power supply terminal is configured to provide a reference ground voltage.
Preferably, the first transistor is an n-type channel field effect transistor, and the second transistor is a p-type channel field effect transistor.
Preferably, the first power supply terminal is configured to provide a reference ground voltage, and the second power supply terminal is configured to provide a power supply voltage.
According to another aspect of the present invention, a buffer circuit is provided, which includes the source follower circuit.
In summary, the source follower circuit and the buffer circuit provided in the embodiments of the present invention include a first transistor and a clamp module, where the first transistor includes an output transistor, and sources (or emitters) and drains (or collectors) of the clamp module and the output transistor are connected to a first node and a second node. The clamping module is used for providing a current path with constant current during the working process of the source follower, and clamping the voltage drop between the first node and the second node to be a constant value, so that the influence of the early effect on the output transistor is eliminated. Meanwhile, the source follower also comprises a first current source which forces the channel current of the output transistor to be unchanged, so that the output voltage Vout can strictly follow the change of the input voltage Vin to change, and the linearity of the source follower is improved. Meanwhile, in the embodiment of the invention, the clamping module is controlled by the output voltage Vout of the source follower, and has a larger output dynamic range.
Drawings
The above and other objects, features and advantages of the present invention will become more apparent from the following description of the embodiments of the present invention with reference to the accompanying drawings.
Fig. 1 shows a circuit schematic of a conventional source follower.
Fig. 2 shows a circuit schematic of a conventional source follower.
Fig. 3 shows a circuit schematic of a source follower according to a first embodiment of the invention.
Fig. 4 shows a circuit schematic of a source follower according to a second embodiment of the invention.
Detailed Description
The invention will be described in more detail below with reference to the accompanying drawings. Like elements in the various figures are denoted by like reference numerals. For purposes of clarity, the various features in the drawings are not necessarily drawn to scale. Moreover, certain well-known elements may not be shown in the figures.
In the following description, numerous specific details of the invention, such as structure, materials, dimensions, processing techniques and techniques of components, are set forth in order to provide a more thorough understanding of the invention. However, as will be understood by those skilled in the art, the present invention may be practiced without these specific details.
It should be understood that in the following description, a "circuit" refers to a conductive loop formed by at least one element or sub-circuit through an electrical or electromagnetic connection. When an element or circuit is referred to as being "connected to" another element or element/circuit is referred to as being "connected between" two nodes, it may be directly coupled or connected to the other element or intervening elements may be present, and the connection between the elements may be physical, logical, or a combination thereof. In contrast, when an element is referred to as being "directly coupled" or "directly connected" to another element, it is intended that there are no intervening elements present.
Fig. 3 shows a circuit schematic of a source follower implemented with a p-type field effect transistor. As shown in fig. 3, the source follower 100 includes a first transistor 110, a clamping module 120, a first current source 130, and a second current source 140. A first terminal of the first current source 130 is connected to the power voltage VDD, and a second terminal of the first current source 130 is connected to the first node P1. The first current source 130 is used to conduct a first bias current Ibias1 from the supply voltage VDD to the first node P1. A first terminal of the second current source 140 is connected to the second node P2, and a second terminal of the second current source 140 is connected to the ground reference. The second current source is used to conduct a second bias current Ibias2 from the second node P2 to ground.
The first transistor 110 is connected between a first node P1 and a second node P2, the input terminal of the first transistor 110 is for receiving an input voltage Vin, and the output terminal is for providing an output voltage Vout. The first transistor 110 includes, for example, a transistor M4, a control terminal of the transistor M4 is configured to receive the input voltage Vin, a first path terminal is connected to the first node P1, and a second path terminal is connected to the second node P2. The first pass terminal of the transistor M4 is used to provide the output voltage Vout. It should be understood that in some circuits, the first node P1 may serve as the output node of the source follower 100.
The clamping module 120 is connected to the first node P1 and the second node P2, and the clamping module 120 is configured to clamp a voltage drop between the first path terminal and the second path terminal of the transistor M4 to a constant value in operation of the source follower 100.
The clamping module 120 includes a resistor R1 and a transistor M5 connected between the power supply voltage VDD and a second node P2, and a control terminal of the transistor M5 is connected to the first node P1.
When the source follower 100 is in operation: when the control terminal of the transistor M5 is activated when receiving the output voltage Vout, the current through the transistor M4 is Ibias1, the current through the transistor M5 is Ibias2-Ibias1, and the voltage drop between the first node P1 and the second node P2 is clamped to a constant value by the transistor M5, thereby eliminating the influence of early effect on the transistor M4. Meanwhile, the first bias current Ibias1 forces the channel current of the transistor M4 to be constant, so that the output voltage Vout strictly follows the variation of the input voltage Vin.
In addition, in the present embodiment, the dynamic range of the output voltage Vout is: -Vgs 1< Vout < VDD-Vdrop, where Vgs1 represents the source-drain voltage of transistor M4 and Vdrop represents the voltage across first current source 130. Vdrop >0.4V, Vgs1 ≈ 0.8V in a typical case, and the dynamic range of the output voltage Vout in the present embodiment is 0.8V to VDD-0.4V in a typical case. Since the transistor M5 in the clamp block 120 provided by the embodiment of the present invention is controlled by the output voltage Vout, the clamp block of the source follower provided by the embodiment of the present invention has a larger dynamic range.
In the above embodiment, the transistor M4 is, for example, a p-type channel field-effect transistor (PFET), and the transistor M5 is, for example, an n-type channel field-effect transistor (NFET). The "control terminal", "first via terminal", and "second via terminal" in the present embodiment are, for example, a "gate", "source", and "drain" of a field effect transistor.
Fig. 4 shows a circuit schematic of a source follower implemented with an n-type field effect transistor. As shown in fig. 4, the source follower 200 includes a first transistor 210, a clamping module 220, a first current source 230, and a second current source 240. A first terminal of the first current source 230 is connected to the first node P1, and a second terminal of the first current source 230 is connected to the ground reference. The first current source 230 is used to conduct a first bias current Ibias1 from the first node P1 to ground. A first terminal of the second current source 240 is connected to the power voltage VDD, and a second terminal of the second current source 240 is connected to the second node P2. The second current source 240 is used to conduct a second bias current Ibias2 from the supply voltage VDD to the second node P2.
The first transistor 210 is connected between a first node P1 and a second node P2, wherein the input terminal of the first transistor 210 is for receiving an input voltage Vin and the output terminal is for providing an output voltage Vout. The first transistor 210 is, for example, a transistor M6, a control terminal of the transistor M6 is configured to receive the input voltage Vin, a first path terminal is connected to the first node P1, and a second path terminal is connected to the second node P2. The first pass terminal of the transistor M6 is used to provide the output voltage Vout. It should be understood that in some circuits, the first node P1 may serve as the output node of the source follower 200.
The clamping module 220 is connected to the first node P1 and the second node P2, and the clamping module 220 is configured to clamp a voltage drop between the first node P1 and the second node P2 to a constant value during operation of the source follower 200.
The clamping module 220 includes a transistor M7 and a resistor R2 connected between the second node P2 and ground, and a control terminal of the transistor M7 is connected to the first node P1.
When the source follower 200 is in operation: when the control terminal of the transistor M7 is activated when receiving the output voltage Vout, the current through the transistor M6 is Ibias1, the current through the transistor M7 is Ibias2-Ibias1, and the voltage drop between the first node P1 and the second node P2 is clamped to a constant value by the transistor M7, thereby eliminating the influence of early effect on the transistor M6. Meanwhile, the first bias current Ibias1 forces the channel current of the transistor M6 to be constant, so that the output voltage Vout strictly follows the variation of the input voltage Vin.
In the above embodiment, the transistor M6 is, for example, an n-type channel field effect transistor (NFET), and the transistor M7 is, for example, a p-type channel field effect transistor (PFET). The "control terminal", "first via terminal", and "second via terminal" in the present embodiment are, for example, a "gate", "source", and "drain" of a field effect transistor.
It should be understood that in the above-described embodiments, the first transistor and the transistors in the clamp module are implemented by field effect transistors, but the present invention is not limited thereto. In other embodiments of the present invention, the first transistor and the transistors in the clamping module may be implemented by bipolar transistors, and the "control terminal", "first via terminal", and "second via terminal" in the embodiments are the "base", "emitter", and "collector" of the bipolar transistors, respectively.
According to another embodiment of the present invention, a buffer circuit is provided, which includes the source follower circuit.
In summary, the source follower and the buffer circuit provided in the embodiments of the present invention include a first transistor and a clamp module, where the first transistor is an output transistor, and sources (or emitters) and drains (or collectors) of the clamp module and the output transistor are connected to a first node and a second node. The clamping module is used for providing a current path with constant current during the working process of the source follower, and clamping the voltage drop between the first node and the second node to be a constant value, so that the influence of the early effect on the output transistor is eliminated. Meanwhile, the source follower also comprises a first current source which forces the channel current of the output transistor to be unchanged, so that the output voltage Vout can strictly follow the change of the input voltage Vin to change, and the linearity of the source follower is improved. Meanwhile, in the embodiment of the invention, the clamping module is controlled by the output voltage Vout of the source follower, and has a larger output dynamic range.
It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
While embodiments in accordance with the invention have been described above, these embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments described. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. The invention is limited only by the claims and their full scope and equivalents.
Claims (9)
1. A source follower circuit, comprising:
a first current source, a first transistor and a second current source connected in sequence between a first power supply terminal and a second power supply terminal, a first path terminal of the first transistor and the first current source being connected to a first node, a second path terminal of the first transistor and the second current source being connected to a second node,
a control terminal of the first transistor receives an input voltage, a first node between the first transistor and the first current source is used for providing an output voltage,
the source follower circuit further comprises a clamping module, wherein a control end of the clamping module receives the output voltage and is used for clamping the voltage drop between the first path end and the second path end of the first transistor to a preset value according to the output voltage.
2. The source follower circuit of claim 1, wherein the clamping module comprises a resistor and a second transistor connected in sequence between the first supply terminal and the second node,
wherein a control terminal of the second transistor is connected to the first node to receive the output voltage.
3. The source follower circuit of claim 2, wherein the second transistor is configured to provide a constant current path from the first supply terminal to the second node when the output voltage is active.
4. The source follower circuit of claim 3, the first current source to provide a first bias current, the second current source to provide a second bias current,
wherein the constant current is a difference between the second bias current and the first bias current.
5. The source follower circuit of claim 4, wherein the first transistor is a p-type channel field effect transistor and the second transistor is an n-type channel field effect transistor.
6. The source follower circuit of claim 5, wherein the first supply terminal is to provide a supply voltage and the second supply terminal is to provide a reference ground voltage.
7. The source follower circuit of claim 4, wherein the first transistor is an n-type channel field effect transistor and the second transistor is a p-type channel field effect transistor.
8. The source follower circuit of claim 7, wherein the first supply terminal is to provide a reference ground voltage and the second supply terminal is to provide a supply voltage.
9. A buffer circuit comprising the source follower circuit of any of claims 1-8.
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| Application Number | Priority Date | Filing Date | Title |
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| CN201810726169.3A CN110687950B (en) | 2018-07-04 | 2018-07-04 | Source follower circuit and buffer circuit |
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| CN201810726169.3A CN110687950B (en) | 2018-07-04 | 2018-07-04 | Source follower circuit and buffer circuit |
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| CN110687950A CN110687950A (en) | 2020-01-14 |
| CN110687950B true CN110687950B (en) | 2020-11-17 |
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| CN111835298B (en) * | 2020-08-10 | 2024-02-06 | 中国电子科技集团公司第二十四研究所 | Differential follower control circuit |
| CN113821069A (en) * | 2021-09-26 | 2021-12-21 | 歌尔微电子股份有限公司 | Source follower, interface circuit and electronic equipment |
| CN115657779B (en) * | 2022-12-08 | 2023-03-21 | 荣湃半导体（上海）有限公司 | Low dropout regulator for suppressing transient sudden change of power supply |
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| TWI263441B (en) * | 2004-01-19 | 2006-10-01 | Sunplus Technology Co Ltd | Circuit for generating reference voltage |
| TWI332748B (en) * | 2004-05-21 | 2010-11-01 | Sunplus Technology Co Ltd | Voltage follower and driving circuit using the same |
| CN100452647C (en) * | 2007-03-23 | 2009-01-14 | 清华大学 | Voltage follower of small output resistance, large output amplitude |
| CN101764584A (en) * | 2009-12-16 | 2010-06-30 | 清华大学 | Linear source follower capable of eliminating bulk effect and channel length modulation effect |
| CN102385407B (en) * | 2011-09-21 | 2013-06-12 | 电子科技大学 | Bandgap reference voltage source |
| CN102591394B (en) * | 2012-02-24 | 2013-11-06 | 电子科技大学 | Bandgap reference voltage source |
| CN106788434B (en) * | 2016-12-19 | 2020-03-17 | 电子科技大学 | Source follower buffer circuit |
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