Operational amplifier, transimpedance amplifier and follower

Abstract

The application provides an operational amplifier, a transimpedance amplifier and a follower, and the operational amplifier comprises an amplifier, a first diode, a second diode and a first electrostatic protection circuit; the first electrostatic protection circuit is connected with a non-inverting input terminal of the amplifier; the first diode and the second diode are connected in reverse-parallel; a positive electrode of the first diode is connected with the first electrostatic protection circuit, and a negative electrode is connected with an inverting input terminal of the amplifier. The application can make a target input pin of the operational amplifier have a very small input current, and meanwhile, effective electrostatic protection is provided.

Description

Technical Field

[0001] This invention relates to the field of integrated circuits, and more particularly to an operational amplifier, a transimpedance amplifier, and a follower. Background Technology

[0002] Operational amplifiers are widely used in various signal conditioning applications. Some of these applications place extremely high demands on the input current at specific input terminals of the op-amp. For example, precision transimpedance amplifiers with extremely large feedback resistors require extremely small input current (in the fA range) at the inverting input terminal of the op-amp; and followers with extremely high input impedance require extremely small input current (in the fA range) at the non-inverting input terminal of the op-amp.

[0003] However, to protect the input stage of the operational amplifier from electrostatic damage, an electrostatic discharge (ESD) protection circuit must be designed. For example... Figure 7 As shown, typical operational amplifiers usually integrate electrostatic discharge (ESD) protection circuits at their two input terminals.

[0004] For operational amplifiers with low input current, the input stage often uses a MOS transistor structure. The gate current of a MOS device is extremely small, so the input current of the op-amp is mainly determined by the leakage current of the input electrostatic discharge (ESD) block.

[0005] There are various forms of electrostatic discharge (ESD) protection circuits, the most common being... Figure 8 As shown, examples include ESD protection diodes connected to two power rails (VDD / VSS) respectively, and thyristor structures. However, the leakage current of these passive ESD devices often only reaches the nanoamp (nA) or picoamp (pA) level, and it is difficult to reduce it to the femtoamp (fA) level.

[0006] Therefore, it is often difficult to achieve both the requirement of ultra-low input current at the target input terminal and the provision of effective electrostatic protection. Summary of the Invention

[0007] One of the objectives of this invention is to address the problems existing in the prior art by providing an operational amplifier, a transimpedance amplifier, and a follower.

[0008] The technical solution provided by this invention is as follows: In a first aspect, this application provides an operational amplifier, comprising: An amplifier, a first diode, a second diode, and a first electrostatic discharge protection circuit; The first electrostatic protection circuit is connected to the non-inverting input terminal of the amplifier; The first diode and the second diode are connected in reverse parallel. The positive terminal of the first diode is connected to the first electrostatic protection circuit, and the negative terminal is connected to the inverting input terminal of the amplifier.

[0009] In some embodiments, a second electrostatic discharge protection circuit and a first resistor are also included; The positive terminal of the first diode is connected to the first electrostatic discharge protection circuit, including: the positive terminal of the first diode is connected to the first electrostatic discharge protection circuit through the first resistor; The positive terminal of the first diode is connected to the second electrostatic protection circuit.

[0010] In some embodiments, the first electrostatic discharge protection circuit includes two diodes connected in series, the two diodes being reverse-connected between the power supply and ground.

[0011] In some embodiments, the first electrostatic discharge protection circuit includes an NMOS transistor; the gate of the NMOS transistor is connected to the source and ground, respectively.

[0012] The above operational amplifier is suitable for use with transimpedance amplifiers, wherein the output terminal of the operational amplifier is connected to the inverting input terminal through a feedback resistor.

[0013] Secondly, this application provides an operational amplifier, comprising: Amplifier, third diode, fourth diode, and first electrostatic discharge protection circuit; The first electrostatic protection circuit is connected to the inverting input terminal of the amplifier; The third diode and the fourth diode are connected in reverse parallel. The positive terminal of the third diode is connected to the first electrostatic protection circuit, and the negative terminal is connected to the non-inverting input terminal of the amplifier.

[0014] In some embodiments, a second electrostatic discharge protection circuit and a second resistor are also included; The positive terminal of the third diode is connected to the first electrostatic protection circuit, including: the positive terminal of the third diode is connected to the first electrostatic protection circuit through the second resistor; The positive terminal of the third diode is connected to the second electrostatic protection circuit.

[0015] In some embodiments, the first electrostatic discharge protection circuit includes two diodes connected in series, the two diodes being reverse-connected between the power supply and ground.

[0016] In some embodiments, the first electrostatic discharge protection circuit includes an NMOS transistor; the gate of the NMOS transistor is connected to the source and ground, respectively.

[0017] The above-mentioned operational amplifier is suitable for use as a follower, wherein the output terminal of the operational amplifier is connected to the inverting input terminal.

[0018] Thirdly, this application provides a transimpedance amplifier, including the operational amplifier described in the first aspect; the output terminal of the operational amplifier is connected to the inverting input terminal through a feedback resistor.

[0019] Fourthly, the present invention also provides a follower, comprising the operational amplifier described in the second aspect; the output terminal of the operational amplifier is connected to the inverting input terminal.

[0020] The operational amplifier, transimpedance amplifier, and follower provided by this invention can bring at least the following beneficial effects: This invention improves upon the traditional ESD structure, resulting in a simple structure that not only provides ultra-low input current at the femtoampere level for the target input pin of the operational amplifier, but also provides effective electrostatic protection for it. Attached Figure Description

[0021] The preferred embodiments will now be explained in a clear and easy-to-understand manner, with reference to the accompanying drawings, to further illustrate the above-mentioned characteristics, technical features, advantages, and implementation methods of the operational amplifier, transimpedance amplifier, and follower.

[0022] Figure 1 This is a schematic diagram of the structure of an embodiment of the operational amplifier of the present invention; Figure 2 This is a schematic diagram of another embodiment of the operational amplifier of the present invention; Figure 3 This is a schematic diagram of another embodiment of the operational amplifier of the present invention; Figure 4 This is a schematic diagram of another embodiment of the operational amplifier of the present invention; Figure 5 This is a schematic diagram of the structure of an embodiment of the transimpedance amplifier of the present invention; Figure 6 This is a schematic diagram of the structure of one embodiment of the follower of the present invention; Figure 7 This is a schematic diagram of a typical input design for an operational amplifier; Figure 8 These are schematic diagrams of two common ESD structures. Detailed Implementation

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0024] To keep the drawings concise, only the parts relevant to the invention are shown schematically in each figure, and they do not represent the actual structure of the product. Furthermore, for ease of understanding, in some figures, components with the same structure or function are shown only schematically, or only one is labeled. In this document, "a" can mean not only "only one" but also "more than one".

[0025] One embodiment of the present invention, such as Figure 1 As shown, an operational amplifier 100 includes: Amplifier U1, first diode D1, second diode D2 and first electrostatic protection circuit 110.

[0026] The anode of the first diode is connected to the first electrostatic protection circuit, and the cathode is connected to the inverting input terminal of amplifier U1. The second diode is connected in parallel with the first diode in reverse, that is, the anode of diode D2 is connected to the cathode of diode D1, and the cathode of diode D2 is connected to the anode of diode D1.

[0027] The non-inverting input terminal INP of amplifier U1 is connected to the first electrostatic discharge (ESD) protection circuit 110, which includes, but is not limited to, […]. Figure 8 The structure type shown is as follows, while the inverting input INM has no ESD protection structure.

[0028] The non-inverting input terminal INP of amplifier U1 is the same as the non-inverting input terminal of operational amplifier 100, and the inverting input terminal INM is the same as the inverting input terminal of operational amplifier 100.

[0029] The operational amplifier 100 provided in this embodiment is suitable for use as a transimpedance amplifier. A transimpedance amplifier is mainly used to convert a weak input current signal into a proportional voltage signal output. The structure of a transimpedance amplifier is as follows: Figure 5 As shown, the output terminal of the operational amplifier 100 is connected to the inverting input terminal through the feedback resistor Rf, and the output voltage of the transimpedance amplifier is equal to the feedback resistor Rf multiplied by the input current Is.

[0030] When operational amplifier 100 is operating normally, its non-inverting and inverting inputs exhibit virtual short characteristics. This means that after output feedback regulation, the voltages at the non-inverting and inverting inputs are equal. Therefore, the voltages across diodes D1 and D2 are equal, with no potential difference, and thus no current flows. From the outside of the operational amplifier, the input current at the inverting input is extremely small, reaching the femtoampere level, while the non-inverting input exhibits a certain amount of input current due to leakage current from the ESD protection structure connected to it.

[0031] When an electrostatic discharge (ESD) occurs at the non-inverting input terminal, the static electricity can be discharged through the ESD protection circuit 110. When an ESD occurs at the inverting input terminal, the static electricity can also be discharged to the ESD protection circuit 110 through diodes D1 or D2, thereby protecting amplifier U1.

[0032] Therefore, this embodiment can provide ultra-low input current at the level of femtoamperes for the inverting input terminal, while providing effective electrostatic protection for both input terminals.

[0033] In one embodiment, the first electrostatic discharge (ESD) protection circuit 110 includes two diodes connected in series, which are reverse-biased between the power supply VDD and ground VSS. The junction of the two diodes is connected to the non-inverting input of the operational amplifier 100. (See also...) Figure 8 .

[0034] In one embodiment, the first electrostatic discharge protection circuit 110 includes a first NMOS transistor. The gate of the first NMOS transistor is connected to both its source and ground VSS, and its drain is connected to the non-inverting input of the operational amplifier 100. (See [link to relevant documentation]). Figure 8 .

[0035] Another embodiment of the present invention, such as Figure 2 As shown, an operational amplifier 100 includes: Amplifier U1, first diode D1, second diode D2, first electrostatic discharge protection circuit 110, second electrostatic discharge protection circuit 120, and first resistor R1.

[0036] The first electrostatic discharge (ESD) protection circuit 110 is connected to the non-inverting input terminal of amplifier U1. The first diode D1 and the second diode D2 are connected in parallel in reverse. The positive terminal of the first diode D1 is connected to the first ESD protection circuit 110 through the first resistor R1, and is also connected to the second ESD protection circuit 120. Its negative terminal is connected to the inverting input terminal of amplifier U1.

[0037] The non-inverting input terminal INP of amplifier U1 is the same as the non-inverting input terminal of operational amplifier 100, and the inverting input terminal INM is the same as the inverting input terminal of operational amplifier 100.

[0038] This embodiment is a further improvement on the previous embodiment, and the provided operational amplifier is also applicable to transimpedance amplifiers.

[0039] In some scenarios, the capacitance across diodes D1 and D2 is very large, resulting in a significant equivalent capacitance between the non-inverting and inverting inputs of the operational amplifier. In the case of a transimpedance amplifier, this capacitance, along with the feedback resistor Rf, introduces a low-frequency pole in the open-loop transfer function, thereby reducing system stability. To address this, a resistor R1 is connected in series between the anode of diode D1 and the first electrostatic discharge (ESD) protection circuit. This introduces a zero in the open-loop transfer function, which cancels out the pole, thus improving system stability. However, adding resistor R1 affects the discharge of electrostatic current to the first ESD protection circuit. Therefore, a second ESD protection circuit is added to provide a low-impedance discharge path for the electrostatic charge, ensuring the effectiveness of ESD protection.

[0040] In one embodiment, both the first electrostatic discharge (ESD) protection circuit and the second ESD protection circuit adopt the following circuit structure: including two series-connected diodes, which are connected in reverse between the power supply VDD and the ground VSS.

[0041] In the first electrostatic discharge (ESD) protection circuit, the connection point of the two diodes is connected to the non-inverting input of the operational amplifier. In the second ESD protection circuit, the connection point of the two diodes is connected to the positive terminal of the first diode D1.

[0042] In one embodiment, both the first electrostatic discharge (ESD) protection circuit and the second ESD protection circuit adopt the following circuit structure: including an NMOS transistor, the gate of which is connected to the source and ground VSS respectively.

[0043] In the first electrostatic discharge (ESD) protection circuit, the drain of the NMOS transistor is connected to the non-inverting input of the operational amplifier. In the second ESD protection circuit, the drain of the NMOS transistor is connected to the anode of the first diode D1.

[0044] Another embodiment of the present invention, such as Figure 3 As shown, an operational amplifier 200 includes: Amplifier U2, third diode D3, fourth diode D4, and first electrostatic protection circuit 210.

[0045] The anode of diode D3 is connected to the first electrostatic discharge protection circuit 210, and the cathode is connected to the non-inverting input terminal of amplifier U2. Diodes D3 and D4 are connected in reverse parallel, that is, the anode of diode D4 is connected to the cathode of diode D3, and the cathode of diode D4 is connected to the anode of diode D3.

[0046] The inverting input of amplifier U2 is connected to the first electrostatic discharge (ESD) protection circuit 210, which includes, but is not limited to, […]. Figure 8The structure type shown is as follows, while the non-inverting input terminal INP does not have an ESD protection structure.

[0047] The non-inverting input terminal INP of amplifier U1 is the same as the non-inverting input terminal of operational amplifier 200, and the inverting input terminal INM is the same as the inverting input terminal of operational amplifier 200.

[0048] The operational amplifier provided in this embodiment is suitable for applications involving voltage followers (also known as voltage followers). The output voltage of the follower precisely "follows" the changes in the input voltage, and the two are in phase and have approximately equal amplitudes. The structure of the follower is as follows: Figure 6 As shown, the output terminal of the operational amplifier 200 is connected to the inverting input terminal.

[0049] When operational amplifier 200 is operating normally, its non-inverting and inverting inputs exhibit virtual short characteristics, meaning that after adjustment by amplifier output feedback, the voltages at the non-inverting and inverting inputs are equal. Therefore, the voltages across the first diode D3 and the second diode D4 are equal, with no potential difference, and thus no current flows. From the outside of the operational amplifier, the input current at the non-inverting input is extremely small, reaching the femtoampere level, while the inverting input, due to leakage current from its connected ESD protection structure, exhibits a certain input current.

[0050] When an electrostatic discharge (ESD) occurs at the inverting input terminal, the static electricity can be discharged through the ESD protection circuit 210. When an ESD occurs at the non-inverting input terminal, the static electricity can also be discharged to the ESD protection circuit 210 through diodes D3 or D4, thereby protecting amplifier U2.

[0051] Therefore, this embodiment can provide ultra-low input current at the level of femtoamperes for the non-inverting input terminal, while providing effective electrostatic protection for both input terminals.

[0052] In one embodiment, the first electrostatic discharge protection circuit includes two diodes connected in series, which are reverse-connected between the power supply VDD and the ground VSS.

[0053] In one embodiment, the first electrostatic discharge protection circuit includes an NMOS transistor, the gate of which is connected to the source and ground VSS.

[0054] Another embodiment of the present invention, such as Figure 4 As shown, an operational amplifier 200 includes: Amplifier U2, third diode D3, fourth diode D4, first electrostatic discharge protection circuit 210, second electrostatic discharge protection circuit 220, second resistor R2.

[0055] The first electrostatic discharge (ESD) protection circuit 210 is connected to the inverting input terminal of amplifier U2. Diodes D3 and D4 are connected in parallel in reverse; the positive terminal of diode D3 is connected to the first ESD protection circuit 210 through the second resistor R2, and is also connected to the second ESD protection circuit 220, while the negative terminal is connected to the non-inverting input terminal of amplifier U2.

[0056] The non-inverting input terminal INP of amplifier U1 is the same as the non-inverting input terminal of operational amplifier 200, and the inverting input terminal INM is the same as the inverting input terminal of operational amplifier 200.

[0057] This embodiment is a further improvement on the previous embodiment, and the provided operational amplifier is also suitable for follower applications.

[0058] In some scenarios, the capacitance across diodes D3 and D4 is very large, resulting in a significant equivalent capacitance between the non-inverting and inverting inputs of the operational amplifier. In the case of a follower, this capacitance interacts with other impedances in the circuit, creating a pole in the loop gain and reducing system stability. To address this, a resistor R2 is connected in series between the anode of diode D3 and the first ESD protection circuit. This introduces a zero into the open-loop transfer function, which cancels out the pole, thus improving system stability. However, adding resistor R2 affects the discharge of electrostatic current to the first ESD protection circuit. Therefore, a second ESD protection circuit is added to provide a low-impedance discharge path for the electrostatic charge, ensuring the effectiveness of ESD protection.

[0059] In one embodiment, both the first electrostatic discharge (ESD) protection circuit and the second ESD protection circuit adopt the following circuit structure: including two diodes connected in series, which are connected in reverse between the power supply and ground.

[0060] In the first ESD protection circuit, the connection point of the two diodes is connected to the inverting input of the operational amplifier. In the second ESD protection circuit, the connection point of the two diodes is connected to the positive terminal of diode D3.

[0061] In one embodiment, both the first electrostatic discharge (ESD) protection circuit and the second ESD protection circuit adopt the following circuit structure: including an NMOS transistor, the gate of which is connected to the source and ground respectively.

[0062] In the first ESD protection circuit, the drain of the NMOS transistor is connected to the inverting input of the operational amplifier. In the second ESD protection circuit, the drain of the NMOS transistor is connected to the anode of diode D3.

[0063] One embodiment of the present invention, such as Figure 5 As shown, a transimpedance amplifier includes an operational amplifier 100 and a feedback resistor Rf. The output terminal of the operational amplifier 100 is connected to the inverting input terminal through the feedback resistor Rf.

[0064] Because the input current at the inverting input of operational amplifier 100 is extremely small, this transimpedance amplifier can detect extremely small current signals.

[0065] One embodiment of the present invention, such as Figure 6 As shown, a follower includes: Operational amplifier 200, the output terminal of operational amplifier 200 is connected to the inverting input terminal.

[0066] By employing operational amplifier 200, the input current at its non-inverting input is extremely small, effectively giving the follower a very high input impedance. When the source impedance Rs of the signal source Vs is large, the output voltage of the follower can match the signal source voltage without generating additional voltage drop.

[0067] It should be noted that the above embodiments can be freely combined as needed. The above are merely preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An operational amplifier characterized by comprising: include: An amplifier, a first diode, a second diode, and a first electrostatic discharge protection circuit; The first electrostatic protection circuit is connected to the non-inverting input terminal of the amplifier; The first diode and the second diode are connected in reverse parallel. The positive terminal of the first diode is connected to the first electrostatic protection circuit, and the negative terminal is connected to the inverting input terminal of the amplifier.

2. An operational amplifier according to claim 1, wherein It also includes a second electrostatic protection circuit and a first resistor; The positive terminal of the first diode is connected to the first electrostatic discharge protection circuit, including: the positive terminal of the first diode is connected to the first electrostatic discharge protection circuit through the first resistor; The positive terminal of the first diode is connected to the second electrostatic protection circuit.

3. An operational amplifier according to claim 1 or 2, characterised in that, The first electrostatic discharge protection circuit includes two diodes connected in series, which are connected in reverse between the power supply and ground.

4. An operational amplifier according to claim 1 or 2, characterized in that The first electrostatic discharge protection circuit includes an NMOS transistor; the gate of the NMOS transistor is connected to the source and ground respectively.

5. An operational amplifier characterized by comprising: include: Amplifier, third diode, fourth diode, and first electrostatic discharge protection circuit; The first electrostatic protection circuit is connected to the inverting input terminal of the amplifier; The third diode and the fourth diode are connected in reverse parallel. The positive terminal of the third diode is connected to the first electrostatic protection circuit, and the negative terminal is connected to the non-inverting input terminal of the amplifier.

6. An operational amplifier according to claim 5, wherein, It also includes a second electrostatic protection circuit and a second resistor; The positive terminal of the third diode is connected to the first electrostatic protection circuit, including: the positive terminal of the third diode is connected to the first electrostatic protection circuit through the second resistor; The positive terminal of the third diode is connected to the second electrostatic protection circuit.

7. An operational amplifier according to claim 5 or 6, characterised in that, The first electrostatic discharge protection circuit includes two diodes connected in series, which are connected in reverse between the power supply and ground.

8. An operational amplifier according to claim 5 or 6, wherein The first electrostatic discharge protection circuit includes an NMOS transistor; the gate of the NMOS transistor is connected to the source and ground respectively.

9. A transimpedance amplifier characterized by, Includes the operational amplifier according to any one of claims 1 to 4; The output terminal of the operational amplifier is connected to the inverting input terminal through a feedback resistor.

10. A follower, characterized by Includes the operational amplifier according to any one of claims 5 to 8; The output terminal of the operational amplifier is connected to the inverting input terminal.

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