Voltage buffer
By introducing a self-biasing circuit into the voltage buffer, providing a self-biasing current to improve the accuracy and loop gain of the voltage buffer, the problem of insufficient reference voltage in the prior art is solved, and the performance of the circuit is significantly improved. Accuracy.
Patent Information
- Application Number
- CN202310770626.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-06-27
- Publication Date
- 2024-12-27
AI Technical Summary
The gain of error amplifiers in existing voltage buffers is limited, resulting in insufficient accuracy of the reference voltage generated, affecting the performance of high-speed and high-precision analog circuits.
A voltage buffer including an amplifier circuit, a negative feedback circuit and a self-biasing circuit is designed to provide a self-biasing current to the amplifier circuit through transistors in the self-biasing circuit, thereby improving the accuracy of the voltage buffer and loop gain.
It effectively improves the accuracy of the reference voltage, makes the input voltage and output voltage of the voltage buffer closer, and improves the performance and accuracy of the circuit.
Smart Images
Figure CN119200725A_ABST
Abstract
Description
Technical Field
[0001] The present disclosure relates to the field of circuits, and in particular to a voltage buffer. Background Art
[0002] With the continuous development of analog circuits, their speed is getting faster and their precision is getting higher, and people's demand for high-speed and high-precision analog circuits is also increasing. Many of these high-speed and high-precision analog circuits require the use of some reference voltages, and the higher the accuracy of these reference voltages, the higher the circuit accuracy and the better the performance. For example, the flash ADC (analog-to-digital converter) circuit uses multiple comparators to convert the input analog signal into a digital signal by comparing the input signal with reference voltages with different thresholds.
[0003] The reference voltage in the prior art is generally generated by voltage buffer and resistor string voltage division. The higher the accuracy of the buffer, the higher the accuracy of the threshold reference voltage generated by the voltage division, and the more accurate the result of the comparator comparison. In the voltage buffer, the error amplifier usually generates the input voltage for processing to obtain the reference voltage. Generally speaking, the accuracy of the reference voltage is closely related to the gain of the error amplifier. Since the error amplifier used in the existing voltage buffer often has limited gain, the reference voltage generated by the voltage buffer is not accurate enough, so it is difficult to achieve high performance of the circuit. Summary of the invention
[0004] The technical problem to be solved by the present disclosure is to provide a voltage buffer in order to overcome the defect that the reference voltage in the prior art is not accurate enough.
[0005] The present invention solves the above technical problems through the following technical solutions:
[0006] A voltage buffer is provided, the voltage buffer comprising an amplifier circuit, a negative feedback circuit and a self-bias circuit;
[0007] The first input terminal of the amplifier circuit is used for inputting voltage, and the output terminal of the amplifier circuit is connected to the second input terminal of the amplifier circuit through the negative feedback circuit to clamp the output voltage of the output terminal to the second input terminal;
[0008] The self-bias circuit includes a first transistor and a second transistor, the input end of the first transistor is connected to the second input end of the amplifier circuit, the output end of the first transistor is connected to the output end of the second transistor, and the output end and input end of the second transistor are connected to the input end of the fifth transistor in the amplifier circuit.
[0009] Preferably, the amplifier circuit comprises a third transistor, a fourth transistor, a fifth transistor, a sixth transistor and a seventh transistor;
[0010] The input end of the third transistor serves as the first input end of the amplifier circuit, the output end of the third transistor serves as the output end of the amplifier circuit, and the input end of the fourth transistor serves as the second input end of the amplifier circuit;
[0011] The control end of the third transistor is electrically connected to the control end of the fourth transistor and the output end of the fifth transistor respectively, the output end of the third transistor is electrically connected to the output end of the sixth transistor, the output end of the fourth transistor is electrically connected to the output end of the seventh transistor; the input end and the output end of the seventh transistor are electrically connected to the input end of the sixth transistor.
[0012] Preferably, the negative feedback circuit further includes an eighth transistor;
[0013] The second input terminal of the amplifier circuit is electrically connected to the output terminal of the eighth transistor, and the output terminal of the amplifier circuit is electrically connected to the input terminal of the first transistor and the input terminal of the eighth transistor respectively.
[0014] Preferably, the channels of the first transistor, the sixth transistor and the seventh transistor have the same width-to-length ratio;
[0015] The channel sizes of the first transistor and the sixth transistor are in a first preset ratio, and / or the channel sizes of the first transistor and the seventh transistor are in a first preset ratio.
[0016] Preferably, the channels of the second transistor and the fifth transistor have the same width-to-length ratio, and the channel sizes of the second transistor and the fifth transistor are in a second preset ratio.
[0017] Preferably, the channels of the first transistor and the eighth transistor have the same width-to-length ratio, and the channel sizes of the first transistor and the eighth transistor are in a third preset ratio.
[0018] Preferably, the negative feedback circuit further includes a resistor and a capacitor;
[0019] The resistor and the capacitor are connected in series between the input terminal and the output terminal of the eighth transistor.
[0020] Preferably, a load is connected to the second input terminal of the amplifier circuit.
[0021] The positive progressive effect of the present disclosure lies in: by adding a self-bias circuit inside the voltage buffer, on the one hand, the transistor in the self-bias circuit provides additional gain for the voltage buffer, and on the other hand, a self-bias circuit is formed inside the voltage buffer to provide a self-bias current to the voltage buffer amplifier circuit, thereby effectively improving the accuracy of the voltage buffer, making the input voltage at the first input terminal of the voltage buffer and the reference voltage output at the output terminal as close as possible, thereby improving the accuracy of the reference voltage and effectively improving the performance of the circuit. BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Figure 1 A schematic diagram of a first connection relationship of a voltage buffer provided in Embodiment 1 of the present disclosure;
[0023] Figure 2 A schematic diagram of a second connection relationship of a voltage buffer provided in Embodiment 1 of the present disclosure. DETAILED DESCRIPTION
[0024] The present disclosure is further described below by way of examples, but the present disclosure is not limited to the scope of the examples.
[0025] Example 1
[0026] Embodiment 1 of the present disclosure provides a voltage buffer. The voltage buffer is a circuit used to protect the load and reduce noise. Its function is to separate the input voltage and the output voltage to prevent the loading effect from interfering with or damaging the input voltage. The voltage buffer is characterized by high input impedance, high output impedance and complete isolation. It can provide electrical isolation and reduce the interference noise between the input voltage and the output voltage to improve the accuracy of the output voltage. Figure 1 and Figure 2 , the voltage buffer includes: an amplifier circuit, a negative feedback circuit and a self-bias circuit;
[0027] The first input terminal 10 of the amplifier circuit is used for inputting voltage, and the output terminal 11 of the amplifier circuit is connected to the second input terminal 12 of the amplifier circuit through a negative feedback circuit to clamp the output voltage of the output terminal 11 to the second input terminal 12 .
[0028] Wherein, the output voltage may be a reference voltage. The voltage buffer provided in this embodiment may be used to generate a higher reference voltage. The amplifier circuit is preferably an error amplifier circuit, and the internal circuit structure adopted by the error amplifier circuit may be a five-tube operational amplifier circuit, but is not limited thereto, and may be selected according to the actual application scenario. When the amplifier circuit is an error amplifier circuit, the first input terminal corresponds to the negative input terminal of the error amplifier circuit, and the second input terminal corresponds to the positive input terminal of the error amplifier circuit.
[0029] The self-bias circuit includes a first transistor 21 and a second transistor 22, wherein the input end of the first transistor 21 is connected to the second input end 12 of the amplifier circuit, the output end of the first transistor 21 is connected to the output end of the second transistor 22, and the output end and input end of the second transistor 22 are connected to the input end of the fifth transistor 15 in the amplifier circuit.
[0030] Among them, the transistor mentioned is preferably a MOS tube (field effect transistor), but is not limited to this and can be selected according to the actual application scenario. Figure 1 The transistor provided in the circuit is an N (semiconductor polarity) channel MOS tube. Figure 2 The transistor provided is a P-channel MOS tube. Figure 1 and Figure 2 The only difference between them is the type of transistors used, and the circuit principles of the two are consistent. When the transistor used is a MOS tube, the input end of the transistor refers to the gate, the output end of the transistor refers to the drain, and the control end of the transistor refers to the source. Figure 1 The voltage buffer provided is generally used to provide a higher voltage reference voltage, while Figure 2 The voltage buffer provided is generally used to provide a lower voltage reference voltage.
[0031] Taking a five-tube operational amplifier circuit as an example, the fifth transistor in a traditional five-tube operational amplifier circuit is generally used as a tail current source. A bias voltage of an external bias circuit is input to the input end of the fifth transistor to provide a bias current to the inside of the five-tube operational amplifier circuit. Since the bias current provided by the external bias circuit does not belong to the current generated by the voltage buffer, its current density is also different from the current density generated inside the voltage buffer. This makes it impossible for the voltage buffer to effectively adjust the circuit according to the clamping state of the output voltage, so that the accuracy of the generated reference voltage is not high. In this embodiment, a current mirror is formed by the first transistor and the second transistor to provide a self-bias current to the fifth transistor, and the five-tube operational amplifier circuit is adjusted according to the circuit conditions of the voltage buffer to ensure that the transistors in the five-tube operational amplifier circuit work in a linear range, so that the fifth transistor as a tail current source can provide a stable tail current for the voltage buffer. When the input voltage changes, the source potential of the fifth transistor will change accordingly to ensure that the current in the amplifier circuit is equal, thereby ensuring the stability of the output reference voltage.
[0032] In this embodiment, a self-bias circuit is provided to provide a self-bias current to the amplifier circuit inside the voltage buffer, thereby effectively improving the accuracy of the voltage buffer. In addition, the loop gain of the voltage buffer can be effectively improved by the transistor in the self-bias circuit. The higher the loop gain of the voltage buffer, the more accurate the voltage clamping at the output end of the amplifier circuit is, and the more accurate the reference voltage output by the amplifier circuit is. The input voltage at the first input end of the voltage buffer and the reference voltage output at the output end are made as close as possible, thereby improving the accuracy of the reference voltage and effectively improving the performance of the circuit.
[0033] In one embodiment, Figure 1 and Figure 2 As shown, the amplifier circuit includes a third transistor 13 , a fourth transistor 14 , a fifth transistor 15 , a sixth transistor 16 and a seventh transistor 17 .
[0034] The input end of the third transistor 13 serves as the first input end 10 of the amplifier circuit, the output end of the third transistor 13 serves as the output end 11 of the amplifier circuit, and the input end of the fourth transistor 14 serves as the second input end 12 of the amplifier circuit.
[0035] The control end of the third transistor 13 is electrically connected to the control end of the fourth transistor 14 and the output end of the fifth transistor 15 respectively. The fifth transistor 15 serves as a tail current source in the amplifier circuit and provides a bias current to the amplifier circuit.
[0036] The output end of the third transistor 13 is electrically connected to the output end of the sixth transistor 16, the output end of the fourth transistor 14 is electrically connected to the output end of the seventh transistor 17, and the input end and the output end of the seventh transistor 17 are electrically connected to the input end of the sixth transistor 16. A set of active current mirrors is formed between the sixth transistor 16 and the seventh transistor 17 to serve as a load in the amplifier circuit.
[0037] In one possible implementation, the negative feedback circuit further includes an eighth transistor 31;
[0038] The second input terminal 12 of the amplifier circuit is electrically connected to the output terminal of the eighth transistor 31, and the output terminal 11 of the amplifier circuit is electrically connected to the input terminal of the first transistor 21 and the input terminal of the eighth transistor 31 respectively to form a negative feedback circuit so that the difference between the output voltage and the input voltage is as small as possible.
[0039] The eighth transistor 31 may also be used as the second stage of an operational amplifier in the voltage buffer to provide circuit gain for the voltage buffer.
[0040] In one embodiment, the channel sizes of the first transistor 21, the sixth transistor 16 and the seventh transistor 17 are in a first preset ratio. In this embodiment, the first preset ratio is preferably 1:1, but it is not limited thereto and can be selected according to actual conditions.
[0041] To facilitate understanding of the aspect ratio and size, the first transistor 21 and the sixth transistor 16 are taken as examples for explanation. The same aspect ratio can be understood as the width of the channel of the first transistor 21: the length of the channel of the first transistor 21 = the width of the channel of the sixth transistor 16: the length of the channel of the sixth transistor 16, and the channel size presenting a first preset ratio can be understood as the width of the first transistor 21: the width of the channel of the sixth transistor 16 = the first preset ratio.
[0042] The second transistor 22 and the fifth transistor 15. The channel sizes of the second transistor 22 and the fifth transistor 15 are in a second preset ratio. In this embodiment, the second preset ratio is preferably 1:2, but it is not limited thereto and can be selected according to actual conditions.
[0043] Since the second transistor 22 and the fifth transistor 15 form a current mirror, the ratio of the current flowing through the second transistor 22 to the current flowing through the fifth transistor 15 is equivalent to the ratio of the channel sizes of the second transistor 22 and the fifth transistor 15, that is, the second preset ratio.
[0044] In addition, the channels of the first transistor 21 and the eighth transistor 31 have the same width-to-length ratio. The channel sizes of the first transistor 21 and the eighth transistor 31 are in a third preset ratio. In this embodiment, the third preset ratio is preferably 1:n.
[0045] Since the first transistor 21 and the eighth transistor 31 form a current mirror, the ratio of the current flowing through the first transistor 21 and the current flowing through the eighth transistor 31 is equivalent to the ratio of the channel sizes of the first transistor 21 and the eighth transistor 31, that is, the third preset ratio.
[0046] When the first preset ratio is 1:1, the second preset ratio is 1:2, and the third preset ratio is 1:n (n can be selected according to actual conditions), the currents flowing through the first transistor 21 and the second transistor 22 are the same, the ratio of the currents flowing through the first transistor 21 and the fifth transistor 15 is 1:2, and the ratio of the currents flowing through the sixth transistor 16 and the fifth transistor is 1:2. Therefore, the currents flowing through the sixth transistor 16 and the first transistor 21 are the same. Because the sixth transistor 16 and the seventh transistor 17 are a set of current mirrors, and the ratio of the channel sizes of the sixth transistor 16 and the seventh transistor 17 is 1:1, that is, the currents flowing through the sixth transistor 16 and the seventh transistor 17 are the same, and thus the currents flowing through the first transistor 21, the sixth transistor 16 and the seventh transistor 17 are the same. The ratio of the currents flowing through the first transistor 21 and the eighth transistor 31 is 1:n, and therefore, the ratio of the currents flowing through the eighth transistor 31 and the sixth transistor 16 or the seventh transistor 17 is 1:n.
[0047] Since the current of the eighth transistor 31 and the sixth transistor 16 and the seventh transistor 17 flows through the corresponding proportional relationship, the gate-source voltage of the eighth transistor 31 is equal to the gate-source voltage of the sixth transistor 16 or the seventh transistor 17, and the gate-source voltage is the voltage between the gate and the source, which can also be understood as the voltage between the input terminal and the control terminal in this embodiment. Since the input terminal of the eighth transistor 31 is connected to the output terminal of the sixth transistor 16, the eighth transistor 31 is equal to the drain-source voltage of the sixth transistor 16, and the drain-source voltage is the voltage between the drain and the source, that is, the voltage between the output terminal and the control terminal. Therefore, it can be obtained that the gate-source voltage of the sixth transistor 16 is equal to its own drain-source voltage, that is, the input terminal voltage of the sixth transistor 16 is equal to the output terminal voltage, and then the closer the output terminal voltages of the sixth transistor 16 and the seventh transistor 17 are, the closer the input terminal voltages of the third transistor 13 and the fourth transistor 14 are, that is, the output voltage of the amplifier circuit is closer to the input voltage, so that the error of the voltage buffer is smaller and the accuracy is higher.
[0048] In one possible implementation, the negative feedback circuit further includes a resistor 32 and a capacitor 33;
[0049] The resistor 32 and the capacitor 33 are connected in series between the input terminal and the output terminal of the eighth transistor 31 to provide Miller compensation to the voltage buffer to improve the amplitude-frequency characteristics of the circuit and increase the stability of the circuit.
[0050] In one embodiment, the second input terminal of the amplifier circuit is connected to a load 34. The eighth transistor 31 can be used as a power transistor to provide a corresponding current to the branch where the load 34 is located.
[0051] Although the specific embodiments of the present disclosure are described above, those skilled in the art should understand that this is only an example, and the protection scope of the present disclosure is defined by the appended claims. Those skilled in the art may make various changes or modifications to these embodiments without departing from the principles and essence of the present disclosure, but these changes and modifications all fall within the protection scope of the present disclosure.
Claims
1. A voltage buffer, characterized in that: The voltage buffer includes an amplifier circuit, a negative feedback circuit and a self-bias circuit; The first input terminal of the amplifier circuit is used for inputting voltage, and the output terminal of the amplifier circuit is connected to the second input terminal of the amplifier circuit through the negative feedback circuit to clamp the output voltage of the output terminal to the second input terminal; The self-bias circuit includes a first transistor and a second transistor, the input end of the first transistor is connected to the second input end of the amplifier circuit, the output end of the first transistor is connected to the output end of the second transistor, and the output end and input end of the second transistor are connected to the input end of the fifth transistor in the amplifier circuit.
2. The voltage buffer according to claim 1, wherein: The amplifier circuit includes a third transistor, a fourth transistor, a fifth transistor, a sixth transistor and a seventh transistor; The input end of the third transistor serves as the first input end of the amplifier circuit, the output end of the third transistor serves as the output end of the amplifier circuit, and the input end of the fourth transistor serves as the second input end of the amplifier circuit; The control end of the third transistor is electrically connected to the control end of the fourth transistor and the output end of the fifth transistor respectively, the output end of the third transistor is electrically connected to the output end of the sixth transistor, the output end of the fourth transistor is electrically connected to the output end of the seventh transistor; the input end and the output end of the seventh transistor are electrically connected to the input end of the sixth transistor.
3. The voltage buffer according to claim 2, characterized in that The negative feedback circuit further includes an eighth transistor; The second input terminal of the amplifier circuit is electrically connected to the output terminal of the eighth transistor, and the output terminal of the amplifier circuit is electrically connected to the input terminal of the first transistor and the input terminal of the eighth transistor respectively.
4. The voltage buffer according to claim 3, characterized in that The channels of the first transistor, the sixth transistor and the seventh transistor have the same width-to-length ratio; The channel sizes of the first transistor and the sixth transistor are in a first preset ratio, and / or the channel sizes of the first transistor and the seventh transistor are in a first preset ratio.
5. The voltage buffer according to claim 3, characterized in that The channels of the second transistor and the fifth transistor have the same width-to-length ratio, and the channel sizes of the second transistor and the fifth transistor are in a second preset ratio.
6. The voltage buffer according to claim 3, characterized in that The channels of the first transistor and the eighth transistor have the same width-to-length ratio, and the channel sizes of the first transistor and the eighth transistor are in a third preset ratio.
7. The voltage buffer according to claim 3, characterized in that The negative feedback circuit also includes a resistor and a capacitor; The resistor and the capacitor are connected in series between the input terminal and the output terminal of the eighth transistor.
8. The voltage buffer according to claim 1, wherein: A load is connected to the second input terminal of the amplifier circuit.