Constant current driver circuit and method of use

Abstract

The application discloses a constant current driving circuit and a use method. The constant current driving circuit comprises a load, a first current source, a second current source, a first resistor, a second resistor, an operational amplifier and a shunt current source. The first end of the first resistor is connected with the output ends of the first current source and the second current source, and the second end of the first resistor is connected with a first preset reference potential. The first end of the second resistor is connected with the input end of the load, and the second end of the second resistor is connected with a second preset reference potential. The noninverting input end of the operational amplifier is connected with the output ends of the first current source and the second current source and the first end of the first resistor, the inverting input end of the operational amplifier is connected with the input end of the load and the first end of the second resistor, and the output end of the operational amplifier is connected with the input end of the load and the first end of the second resistor. The shunt current source is connected with the input end of the load and the output end of the operational amplifier. The first current source and the shunt current source are adjustable current sources.

Description

Technical Field

[0001] This invention relates to the field of electronic circuit technology, and in particular to a constant current driving circuit and its usage method. Background Technology

[0002] In traditional constant current drive circuits, there are usually two factors that determine the accuracy of the circuit's output current: the matching degree of the sensing resistor and the offset voltage of the amplifier. The matching degree of the sensing resistor can be improved by increasing the resistor area and optimizing the layout.

[0003] The amplifier's offset voltage (Vos, Voltage-Input Offset) includes system offset voltage and random offset voltage. System offset voltage can be reduced by increasing the gain; random offset voltage is generally reduced by increasing the device area, but this also increases the device's parasitic capacitance and reduces the system response speed. Furthermore, random offset voltage can be eliminated through dynamic methods such as chopping or automatic zeroing, but this increases circuit complexity and causes output current jitter, reducing system reliability. Therefore, it is necessary to adjust the traditional constant current drive circuit. Summary of the Invention

[0004] The purpose of this invention is to provide a constant current drive circuit and its usage method. By increasing the input common-mode voltage of the operational amplifier, the phenomenon of no current output caused by the offset voltage of the operational amplifier when the input current is small can be eliminated, thereby eliminating the offset error present in traditional constant current drive circuits.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0006] A constant current drive circuit, comprising:

[0007] load;

[0008] The first current source is used to output the first current;

[0009] The second current source is used to output the second current.

[0010] The first resistor has its first end connected to the output terminals of the first current source and the second current source, and its second end connected to the first preset reference potential.

[0011] The second resistor has its first end connected to the input terminal of the load and its second end connected to the second preset reference potential.

[0012] An operational amplifier, with its non-inverting input connected to the outputs of the first current source, the second current source, and the first terminal of the first resistor, its inverting input connected to the input of the load and the first terminal of the second resistor, and its output connected to the input of the load and the first terminal of the second resistor, is used to amplify the first current and the second current and then supply them to the load; and

[0013] A shunt current source is connected to the input terminal of the load and the output terminal of the operational amplifier to shunt the current supplied to the load so that the current flowing through the load is the amplified first current; and both the first current source and the shunt current source are adjustable current sources.

[0014] Optionally, the operational amplifier has an offset voltage, and the relationship between the second current, the first resistor, and the offset voltage is as follows:

[0015] IR*R1>>|Voffset|

[0016] Wherein, IR represents the current value of the second current; R1 represents the resistance value of the first resistor; and |Voffset| represents the offset voltage.

[0017] Optionally, the potential difference between the first preset reference potential and the second preset reference potential is 0.

[0018] Optionally, the resistance ratio of the first resistor and the second resistor is a preset ratio.

[0019] Optionally, the constant current driving circuit further includes: a MOS transistor; the gate of the MOS transistor is connected to the output terminal of the operational amplifier, the source of the MOS transistor is connected to the inverting input terminal of the operational amplifier and the first terminal of the second resistor; the drain of the MOS transistor is connected to the input terminal of the load and the input terminal of the shunt current source.

[0020] Optionally, the MOS transistor is an N-type MOS transistor.

[0021] Based on the same inventive concept, this embodiment also provides a method of using the constant current driving circuit as described above, including:

[0022] Turn off the first current source and the shunt current source;

[0023] The second current source outputs the second current, and the operational amplifier delivers the amplified second current to the load;

[0024] Turn on and regulate the shunt current source to shunt the amplified second current supplied to the load; and stop regulating the shunt current source when the current flowing through the load is 0, that is, fix the value of the shunt current source at this time;

[0025] Turn on the first current source to output the first current source.

[0026] Compared with the prior art, the present invention has at least one of the following advantages:

[0027] The present invention provides a constant current driving circuit and its usage method, wherein a second current source and a shunt current source are connected to the input and output terminals of the circuit, respectively; wherein, the second current source can boost the input common-mode voltage of the operational amplifier; and the shunt current source can shunt the extra current generated by the second current source, so that the current flowing through the load is still the amplified first current, thereby preventing the circuit from having offset errors and ensuring the normal operation of the load.

[0028] This invention can raise the input common-mode voltage of the operational amplifier while ensuring the high linearity of the traditional constant current drive circuit. This eliminates the phenomenon of no current output caused by the offset voltage of the operational amplifier when the first current source has a small current input, thus eliminating the offset error present in the traditional constant current drive circuit.

[0029] This invention provides a method for eliminating output current offset error without relying on a low offset operational amplifier. By raising the input common-mode voltage of the operational amplifier, its common-mode voltage is greater than the offset voltage even under low current output, and the circuit will not enter an abnormal operating state. The offset error is eliminated while maintaining the performance of a traditional constant current drive circuit. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of a constant current drive circuit provided in an embodiment of the present invention;

[0031] Figure 2 This is a graph showing the changes in the first and second voltages with the first current under different polarity offset voltages in a traditional constant current drive circuit.

[0032] Figure 3 This is a graph showing the results of the first voltage and the second voltage changing with the first current under different polarity offset voltages in a constant current drive circuit provided by an embodiment of the present invention.

[0033] Figure 4 This is a comparison diagram of the effects of a constant current driving circuit provided in an embodiment of the present invention and a traditional constant current driving circuit. Detailed Implementation

[0034] The following detailed description, in conjunction with the accompanying drawings and specific embodiments, provides a further detailed explanation of the constant current driving circuit and its usage method proposed in this invention. The advantages and features of this invention will become clearer from the following description. It should be noted that the accompanying drawings are in a very simplified form and use non-precise proportions, used only to facilitate and clearly illustrate the embodiments of this invention. Please refer to the accompanying drawings to make the objectives, features, and advantages of this invention more apparent and understandable. It should be understood that the structures, proportions, sizes, etc., depicted in the accompanying drawings are only for illustrative purposes to aid those skilled in the art and are not intended to limit the implementation conditions of this invention. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to the size, without affecting the effects and objectives achieved by this invention, should still fall within the scope of the technical content disclosed in this invention.

[0035] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0036] Combined with appendix Figures 1-3As shown, this embodiment provides a constant current driving circuit, including: a load 100; a first current source 110 for outputting a first current; a second current source 120 for outputting a second current; a first resistor 151, the first end of which is connected to the output terminals of the first current source 110 and the second current source 120, and the second end of which is connected to a first preset reference potential; a second resistor 152, the first end of which is connected to the input terminal of the load 100, and the second end of which is connected to a second preset reference potential; and an operational amplifier OPA, the non-inverting input terminal of which is connected to the output terminal of the first current source 110, the output terminal of the second current source 120, and the first resistor 151. One end is connected, with its inverting input terminal connected to the input terminal of the load 100 and the first terminal of the second resistor 152, and its output terminal connected to the input terminal of the load 100 and the first terminal of the second resistor 152, for amplifying the first current and the second current and then sending them to the load 100; and a shunt current source 130, connected to the input terminal of the load 100 and the output terminal of the operational amplifier OPA, for shunting the current sent to the load 100 so that the current flowing through the load 100 is the amplified first current; and both the first current source 110 and the shunt current source 130 are adjustable current sources.

[0037] Specifically, the first current source 110 is the current source that enables the load 100 to operate normally; that is, the amplified first current, after being processed by the operational amplifier OPA and delivered to the load 100, is the normal operating current of the load 100. Optionally, the resistance ratio R1 / R2 of the first resistor 151 and the second resistor 152 is a preset ratio to control the current amplification factor of the operational amplifier OPA; where R1 represents the resistance value of the first resistor 151, and R2 represents the resistance value of the second resistor 152, and the preset ratio can be set according to specific requirements. Preferably, the preset ratio is not less than 50, for example, 50, 100, 200, etc. In addition, the operational amplifier OPA typically has an offset voltage |Voffset|.

[0038] In a traditional constant current drive circuit, a typical component includes a load 100, a first current source 110, a first resistor 151, a second resistor 152, and an operational amplifier (OPA). Specifically, in an ideal scenario, the first current source 110 injects a current (the first current) into the first resistor 151, generating a first voltage V1 (the input common-mode voltage of the operational amplifier) ​​across the first resistor 151. Simultaneously, the operational amplifier (OPA) applies a second voltage V2 across the second resistor 152 through negative feedback, and the first voltage V1 equals the second voltage V2 (ideally). In this case, the current amplification factor Ai of the operational amplifier (OPA) is Ai = R1 / R2. However, in a traditional constant current drive circuit, the current value I_IN of the first current output by the first current source 110 varies within a wide range, causing the first voltage V1 to also vary within a wide range. When the condition that the first voltage V1 >> the offset voltage |Voffset| is not met, the relative amount by which the second voltage V2 deviates from the first voltage V1 increases (e.g., ...). Figure 2 As shown, V2+ and V2- represent the second voltages under different polarity offset voltages, which causes the current amplification factor of the traditional constant current drive circuit to deviate significantly from Ai, but the amplification factor of the current change is still Ai, resulting in an offset error; that is to say, the intercept of the linear function of the input and output of the traditional constant current drive circuit is affected by |Voffset|, but the slope is still Ai.

[0039] Based on the above analysis of the offset error problem in traditional constant current drive circuits, it can be found that the cause of the offset error in traditional constant current drive circuits is that the first voltage V1 may be less than the offset voltage |Voffset|. Therefore, in this embodiment, a solution is considered to raise the first voltage V1, i.e., the input common-mode voltage of the operational amplifier, so that it is always greater than the offset voltage |Voffset| to avoid the offset error in the circuit.

[0040] Specifically, such as Figure 1 As shown, compared to traditional constant current drive circuits, the constant current drive circuit provided in this embodiment directly connects the second current source 120 and the shunt current source 130 to the input and output terminals of the circuit, respectively. The second current source 120 can boost the first voltage V1, while the shunt current source 130 can divert the extra current generated by the second current source 120, so that the current flowing through the load 100 is still the first current amplified by a preset factor. This not only prevents the circuit from having an offset error, but also ensures that the load 100 works normally.

[0041] More specifically, in this embodiment, the relationship between the second current, the first resistance, and the offset voltage is as follows:

[0042] IR*R1>>|Voffset|

[0043] Wherein, IR represents the current value of the second current; R1 represents the resistance value of the first resistor 151; |Voffset| represents the absolute value of the offset voltage; >> indicates much greater than.

[0044] In this embodiment, by raising the first voltage V1 to V1 = IR*R1 when the output of the first current source 110 is 0, and setting IR*R1 >> |Voffset|, the offset error of the circuit when the first current source 110 is at a small current can be effectively avoided (e.g., Figure 3 As shown, when I_IN is 0, V1, V2+, and V2- are all raised to a level greater than |Voffset|. Optionally, the selection of the second current source 120 must not only meet the requirement of IR*R1>>|Voffset|, but also meet the acceptable additional power consumption requirement; the shunt current source 130 can be a variable current source configured through a register, such as a current source controlled by digital code, but the present invention is not limited thereto.

[0045] Please continue to refer to this. Figure 1 The constant current driving circuit further includes: a MOS transistor 140; the gate of the MOS transistor 140 is connected to the output terminal of the operational amplifier OPA, the source of the MOS transistor 140 is connected to the inverting input terminal of the operational amplifier OPA and the first terminal of the second resistor 152; the drain of the MOS transistor 140 is connected to the input terminal of the load 100 and the input terminal of the shunt current source 130.

[0046] Specifically, in this embodiment, the MOS transistor 140 forms a negative feedback circuit with the operational amplifier OPA, such that the current flowing through the first resistor 151 and the second resistor 152 is proportional to their resistance values. Optionally, the MOS transistor 140 is an N-type MOS transistor; and the potential difference between the first preset reference potential and the second preset reference potential is 0, but the present invention is not limited thereto.

[0047] Based on the same inventive concept, this embodiment also provides a method for using the constant current driving circuit as described above, including: step S1, turning off the first current source 110 and the shunt current source 130; step S2, causing the second current source 120 to output the second current, and the operational amplifier OPA to send the amplified second current to the load 100; step S3, turning on and regulating the shunt current source 130 to shunt the amplified second current sent to the load 100; and stopping the regulation of the shunt current source 130 when the current value flowing through the load 100 is 0, that is, fixing the value of the shunt current source 130 at this time; step S4, turning on the first current source 110 to output the first current source.

[0048] Specifically, in this embodiment, in step S1, by performing the operation of turning off the first current source 110 and the shunt current source 130, the output of the first current source 110 can be set to 0 and the output of the shunt current source 130 can also be set to 0.

[0049] In step S2, the second current that meets the conditions can be injected. At this time, the current flowing through the load 100 is the second current after being amplified by the operational amplifier OPA.

[0050] In step S3, the output IR_LOAD of the shunt current source 130 can be increased from 0, so that the value of the current I_LOAD flowing through the load 100 gradually decreases; when the value of the current I_LOAD flowing through the load 100 is exactly 0, the adjustment of the shunt current source 130 is stopped, and the value of the shunt current source 130 is fixed at this time.

[0051] In step S4, after the first current source 110 is turned on, as the value of the first current I_IN output by the first current source 100 changes, the value of the current flowing through the load 100 satisfies I_LOAD=I_IN*(R1 / R2). At this time, the constant current drive circuit enters a working state without offset error, that is, the offset error existing in the traditional constant current drive circuit is eliminated.

[0052] Furthermore, the magnitude and polarity of the offset voltage |Voffset| of the operational amplifier OPA only affect the adjustment value of the shunt current source 130. Therefore, the accuracy of offset error elimination depends on the adjustment accuracy of the shunt current source 130. Moreover, the adjustment accuracy of the shunt current source 130 depends on the accuracy at which the adjustment of the shunt current source 130 is stopped when the value of the current I_LOAD flowing through the load is exactly 0, and the value of the shunt current source 130 is fixed at this time. However, the present invention is not limited thereto.

[0053] Furthermore, Figure 4 The graph shows the relationship between the input and output current functions. Figure 4 The dashed lines ① and ③ in the figure represent the input-output function relationship curves of the traditional constant current drive circuit under different polarity offset voltages, which represent the offset error; the solid line ② is the input-output function relationship curve of the constant current drive circuit provided in this embodiment, which is equivalent to eliminating the constant term in the transfer function of the traditional constant current drive circuit. It can be seen from this that the constant current drive circuit provided in this embodiment effectively eliminates the offset error that exists in the traditional constant current drive circuit.

[0054] In summary, this embodiment provides a constant current driving circuit and its usage method. A second current source and a shunt current source are connected to the input and output terminals of a traditional constant current driving circuit, respectively. The second current source can boost the input common-mode voltage of the operational amplifier; the shunt current source can divert the extra current generated by the second current source, ensuring that the current flowing through the load remains the amplified first current. This prevents offset errors in the circuit and ensures normal load operation. This embodiment can boost the input common-mode voltage of the operational amplifier while maintaining the high linearity of the traditional constant current driving circuit, thereby eliminating the phenomenon of no current output due to the offset voltage of the operational amplifier at low current inputs, thus eliminating the offset error present in traditional constant current driving circuits.

[0055] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A constant current drive circuit, characterized in that, include: load; The first current source is used to output the first current; The second current source is used to output the second current. The first resistor has its first end connected to the output terminals of the first current source and the second current source, and its second end connected to the first preset reference potential. The second resistor has its first end connected to the input terminal of the load and its second end connected to the second preset reference potential. An operational amplifier has its non-inverting input connected to the output of the first current source, the output of the second current source, and the first end of the first resistor; its inverting input connected to the input of the load and the first end of the second resistor; and its output connected to the input of the load and the first end of the second resistor. It is used to amplify the first current and the second current and then send them to the load. as well as A shunt current source is connected to the input terminal of the load and the output terminal of the operational amplifier to shunt the current supplied to the load so that the current flowing through the load is the amplified first current; and both the first current source and the shunt current source are adjustable current sources.

2. The constant current drive circuit as described in claim 1, characterized in that, The operational amplifier has an offset voltage, and the relationship between the second current, the first resistor, and the offset voltage is as follows: IR*R1>>|Voffset| Wherein, IR represents the current value of the second current; R1 represents the resistance value of the first resistor; and |Voffset| represents the offset voltage.

3. The constant current drive circuit as described in claim 1, characterized in that, The potential difference between the first preset reference potential and the second preset reference potential is 0.

4. The constant current drive circuit as described in claim 1, characterized in that, The resistance ratio between the first resistor and the second resistor is a preset ratio.

5. The constant current drive circuit as described in claim 1, characterized in that, Also includes: A MOS transistor; the gate of the MOS transistor is connected to the output terminal of the operational amplifier, the source of the MOS transistor is connected to the inverting input terminal of the operational amplifier and the first terminal of the second resistor; the drain of the MOS transistor is connected to the input terminal of the load and the input terminal of the shunt current source.

6. The constant current drive circuit as described in claim 5, characterized in that, The MOS transistor is an N-type MOS transistor.

7. A method of using the constant current drive circuit as described in any one of claims 1 to 6, characterized in that, include: Turn off the first current source and the shunt current source; The second current source outputs the second current, and the operational amplifier delivers the amplified second current to the load; Turn on and regulate the shunt current source to shunt the amplified second current supplied to the load; Furthermore, the regulation of the shunt current source is stopped when the current flowing through the load is 0. Turn on the first current source to output the first current source.

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