An instrument amplifier with active protection drive

Abstract

The present disclosure provides an instrument amplifier with active protection drive, which introduces an active protection drive circuit outside the instrument amplification core circuit, so that the signal transmission line shielding layer potential follows the output potential of the input buffer circuit, thereby reducing the equivalent potential difference between the signal line core and the shielding layer, reducing the shunt effect caused by the parasitic capacitance, and further improving the effective bandwidth of the high impedance sensor measurement system; At the same time, the phase compensation network is arranged in the feedback loop of the protection drive amplifier, and the loop phase when driving the capacitive load is compensated, which can suppress ringing and oscillation, improve system stability and signal-to-noise ratio, and enhance the applicability and adjustability of the circuit under different cable lengths and parasitic capacitance conditions.

Description

Technical Field

[0001] This disclosure relates to the field of electronic measurement and signal conditioning technology, and more specifically, to an instrumentation amplifier with active protection drive. Background Technology

[0002] In applications such as precision instruments, medical testing, industrial automation, and scientific experiments, sensors with high output impedance and small output signal amplitude are widely used, such as photodiodes, pH electrodes, ion-selective electrodes, photomultiplier tubes, and some bioelectric sensors. These high-impedance sensors typically have a large equivalent output impedance, and their output signals often exhibit nanoampere-level current or millivolt-level voltage characteristics. To avoid loading effects on the sensor signal and ensure measurement accuracy, the front-end amplifier circuit usually needs to have high input impedance, low input bias current, and good common-mode rejection capability. Therefore, instrumentation amplifiers are often used for front-end signal amplification and differential signal conversion of these high-impedance sensors.

[0003] However, in practical measurement systems using high-impedance sensors, the sensor output and amplifier input are typically connected via cables or traces. These signal transmission lines inevitably introduce parasitic capacitance to ground and distributed capacitance between the signal core and the shielding layer. Simultaneously, the amplifier input and device packaging also introduce input capacitance. These parasitic capacitances, together with the sensor's high output impedance, form an equivalent low-pass network, significantly limiting the system's bandwidth. This leads to attenuation of high-frequency signal components, making it difficult to meet the measurement requirements of dynamically changing signals, and further causing phase delay and waveform distortion. Summary of the Invention

[0004] This disclosure provides at least one embodiment of an instrumentation amplifier with active protection drive. By introducing an active protection drive circuit outside the core circuit of the instrumentation amplifier, the potential of the signal transmission line shielding layer follows the output potential of the input buffer circuit, thereby reducing the equivalent potential difference between the signal core and the shielding layer, reducing the shunting effect caused by parasitic capacitance, and thus improving the effective bandwidth of the high-impedance sensor measurement system. At the same time, a phase compensation network is set in the feedback loop of the protection drive amplifier to compensate for the loop phase when driving capacitive loads, which can suppress ringing and oscillation, improve system stability and signal-to-noise ratio, and enhance the applicability and adjustability of the circuit under different cable lengths and parasitic capacitance conditions.

[0005] This disclosure provides an instrumentation amplifier with active protection drive, including: a sensor input port, a sensor output port, a signal transmission line connected to the sensor input port, an instrumentation amplifier core circuit, an active protection drive circuit, and a phase compensation network. The instrumentation amplifier core circuit includes an input buffer circuit and a differential amplifier circuit. The input buffer circuit includes a first input amplifier and a second input amplifier. The input terminal of the first input amplifier is electrically connected to the first signal terminal of the sensor input port, and the input terminal of the second input amplifier is electrically connected to the second signal terminal of the sensor input port. The differential amplifier circuit includes a third amplifier and a resistor network. The resistor network is electrically connected to the inverting input terminal and the non-inverting input terminal of the third amplifier, and is also electrically connected to the output terminals of the first input amplifier and the second input amplifier, respectively, so as to convert the differential signal output by the first input amplifier and the second input amplifier into the output signal at the sensor output port. The active protection drive circuit includes a protection drive amplifier. The input terminal of the protection drive amplifier is electrically connected to the output terminal of the first input amplifier to obtain a drive signal corresponding to the sensor input signal. The output terminal of the protection drive amplifier is electrically connected to the shielding layer of the signal transmission line to drive the potential of the shielding layer to follow the drive signal. The phase compensation network is set in the feedback loop of the protection drive amplifier and is used to compensate the loop phase when the protection drive amplifier drives a capacitive load.

[0006] In one optional embodiment, both the first input amplifier and the second input amplifier are configured as voltage follower structures, with their outputs directly fed back to their respective inverting inputs, and their respective non-inverting inputs constituting the first signal terminal and the second signal terminal of the sensor input port, respectively.

[0007] In one optional embodiment, the input buffer circuit further includes a gain setting impedance, which is connected between the output terminal of the first input amplifier and the output terminal of the second input amplifier, and is used to set the differential gain of the front stage of the instrumentation amplification core circuit. The gain setting impedance is a gain setting resistor, one end of which is electrically connected to the output terminal of the first input amplifier, and the other end is electrically connected to the output terminal of the second input amplifier.

[0008] In one optional embodiment, the resistor network includes a first resistor, a second resistor, a third resistor, and a fourth resistor; The first resistor and the second resistor are matching resistors, and the third resistor and the fourth resistor are matching resistors; The inverting input terminal of the third amplifier is electrically connected to the output terminal of the first input amplifier via the first resistor, and is also electrically connected to the sensor output port via the third resistor. The non-inverting input terminal of the third amplifier is electrically connected to the output terminal of the second input amplifier via the second resistor, and is electrically connected to the reference potential terminal via the fourth resistor.

[0009] In one alternative implementation, the protection drive amplifier is configured as a unity-gain buffer; The output of the unity-gain buffer is fed back to the inverting input, and the non-inverting input constitutes the input of the protection drive amplifier.

[0010] In one optional embodiment, the phase compensation network includes a compensation capacitor connected in parallel between the output terminal and the inverting input terminal of the protection drive amplifier; The compensation capacitor is an adjustable capacitor used to adjust the trade-off between stability margin and bandwidth when the cable length or parasitic capacitance changes.

[0011] In one optional implementation, an isolation resistor is connected in series between the input terminal of the protection drive amplifier and the output terminal of the first input amplifier to reduce the load coupling of the active protection drive circuit to the output terminal of the first input amplifier.

[0012] In one optional embodiment, the signal transmission line includes a signal core and a shielding layer; The signal wire core is electrically connected to the sensor input port and connected to the first input amplifier or the second input amplifier; The shielding layer is electrically connected to the output terminal of the protection drive amplifier so that the potential of the shielding layer follows the potential of the signal core, thereby reducing the equivalent potential difference between the signal core and the shielding layer.

[0013] In one alternative implementation, the shielding layer is replaced with an independent protective conductor; The independent protective conductor is laid along the signal core and electrically connected to the output terminal of the protective drive amplifier to neutralize the parasitic capacitance around the signal core.

[0014] In one optional embodiment, the input sampling point of the protection drive amplifier is the output terminal of the first input amplifier, and the output terminal of the protection drive amplifier drives the shielding layer so that the potential of the shielding layer is equal to the output potential of the first input amplifier.

[0015] This disclosure provides an instrumentation amplifier with active protection drive. By introducing an active protection drive circuit outside the core circuit of the instrumentation amplifier, the potential of the signal transmission line shielding layer follows the output potential of the input buffer circuit, thereby reducing the equivalent potential difference between the signal core and the shielding layer, reducing the shunting effect caused by parasitic capacitance, and thus improving the effective bandwidth of the high-impedance sensor measurement system. At the same time, a phase compensation network is set in the feedback loop of the protection drive amplifier to compensate for the loop phase when driving capacitive loads, which can suppress ringing and oscillation, improve system stability and signal-to-noise ratio, and enhance the applicability and adjustability of the circuit under different cable lengths and parasitic capacitance conditions.

[0016] To make the above-mentioned objects, features and advantages of this disclosure more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. These drawings are incorporated in and constitute a part of this specification. They illustrate embodiments conforming to this disclosure and, together with the specification, serve to explain the technical solutions of this disclosure. It should be understood that the following drawings only show some embodiments of this disclosure and should not be considered as limiting the scope. Those skilled in the art can obtain other related drawings based on these drawings without creative effort.

[0018] Figure 1 This diagram illustrates an equivalent model of a high-impedance sensor connected to an amplifier, as provided in an embodiment of this disclosure. Figure 2 A circuit schematic of an instrumentation amplifier with active protection drive provided in an embodiment of this disclosure is shown. Figure 3 A circuit schematic of another instrumentation amplifier with active protection drive provided in an embodiment of this disclosure is shown. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this disclosure, and not all of them. The components of the embodiments of this disclosure described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this disclosure provided in the accompanying drawings is not intended to limit the scope of the claimed disclosure, but merely represents selected embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without inventive effort are within the scope of protection of this disclosure.

[0020] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0021] In this document, the term "and / or" merely describes a relationship, indicating that three relationships can exist. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Furthermore, the term "at least one" in this document means any combination of at least two of any one or more elements. For example, including at least one of A, B, and C can mean including any one or more elements selected from the set consisting of A, B, and C.

[0022] Research has revealed that in practical measurement systems using high-impedance sensors, the sensor output and amplifier input are typically connected via cables or traces. These signal transmission lines inevitably introduce parasitic capacitance to ground and distributed capacitance between the signal core and the shielding layer. Simultaneously, the amplifier input and device packaging also introduce input capacitance. These parasitic capacitances, together with the sensor's high output impedance, form an equivalent low-pass network, significantly limiting the system's bandwidth. This leads to attenuation of high-frequency signal components, making it difficult to meet the measurement requirements of dynamically changing signals, and further causing phase delay and waveform distortion.

[0023] Based on the above research, this disclosure provides an instrumentation amplifier with active protection drive. This application introduces an active protection drive circuit outside the core circuit of the instrumentation amplifier, so that the potential of the shielding layer of the signal transmission line follows the output potential of the input buffer circuit, thereby reducing the equivalent potential difference between the signal core and the shielding layer, reducing the shunting effect caused by parasitic capacitance, and thus improving the effective bandwidth of the high-impedance sensor measurement system. At the same time, a phase compensation network is set in the feedback loop of the protection drive amplifier to compensate for the loop phase when it drives capacitive loads, which can suppress ringing and oscillation, improve system stability and signal-to-noise ratio, and enhance the applicability and adjustability of the circuit under different cable lengths and parasitic capacitance conditions.

[0024] To facilitate understanding of this embodiment, a detailed description of an instrumentation amplifier with active protection drive disclosed in this disclosure embodiment will be provided first. See [link to relevant documentation]. Figure 1 The diagram shown is an equivalent model of a high-impedance sensor and amplifier connection provided in an embodiment of this disclosure.

[0025] like Figure 1 As shown, a high-impedance sensor can be equivalent to a combination of a signal source and a high output impedance. The signal source can be a current source or a voltage source, used to characterize the weak output signal generated by the sensor. The high output impedance is characterized by the equivalent output resistance Rs, which is located between the sensor output node and the reference potential, and is used to characterize the high equivalent source impedance characteristics of the sensor.

[0026] Here, the signal transmission path connected to the sensor output node (such as connecting cables, connectors, and PCB traces) inevitably introduces parasitic capacitance. Parasitic capacitance includes the sensor's own junction capacitance, amplifier input capacitance, and the capacitance of the signal transmission line to ground. Figure 1 The equivalent ground parasitic capacitance Cp is used to characterize the capacitance. When a cable connection is used, the distributed capacitance of the cable can be further characterized by C_cable, and it works together with the parasitic capacitance Cp on the sensor output node.

[0027] In this equivalent model, the equivalent output resistance Rs and the parasitic capacitance to ground Cp (and / or C_cable) constitute a single-pole low-pass network in the AC sense, which makes the sensor output node exhibit a stronger bypass effect on high-frequency signal components, thereby limiting the effective measurement bandwidth of the subsequent amplifier.

[0028] Specifically, the cutoff frequency of a low-pass network can be approximately given by the following formula: fc = 1 / (2π·Rs·Cp); when the distributed capacitance of the cable is further considered, the cutoff frequency can be approximated by fc = 1 / (2π·Rs·(Cp+C_cable)). Since the Rs of high-impedance sensors is usually on the order of a high magnitude, even if Cp or C_cable is small, it will cause fc to decrease significantly, resulting in attenuation of high-frequency components of the signal and deterioration of dynamic response.

[0029] Furthermore, in some applications, the amplifier front-end can use a feedback resistor Rf to form a feedback network (e.g., a transimpedance / feedback amplification structure). In this case, the parasitic capacitance Cp and the cable distributed capacitance C_cable may also form a pole in the feedback loop together with the feedback resistor Rf, further reducing the system bandwidth and introducing phase lag, causing ringing or instability risks at the output. Therefore, it is evident that... Figure 1 The parasitic capacitance and high source impedance coupling effect shown are one of the main sources of bandwidth bottleneck in high-impedance sensor interface circuits.

[0030] Further, see Figure 2 The diagram shown is a circuit schematic of an instrumentation amplifier with active protection drive provided in an embodiment of this disclosure.

[0031] like Figure 2 As shown in the embodiments of this disclosure, the instrumentation amplifier with active protection drive, taking a photodiode as a high-impedance sensor as an example (it can also be a pH electrode, ion-selective electrode, photomultiplier tube, and some bioelectric sensors, etc.), includes: a sensor input port, a sensor output port, a signal transmission line connected to the sensor input port, an instrumentation amplifier core circuit, and an active protection drive circuit. The instrumentation amplifier core circuit includes an input buffer circuit and a differential amplifier circuit.

[0032] Specifically, the input buffer circuit includes a first input amplifier A1 and a second input amplifier A2. The input terminal of the first input amplifier A1 is electrically connected to the first signal terminal of the sensor input port, and the input terminal of the second input amplifier A2 is electrically connected to the second signal terminal of the sensor input port. The differential amplifier circuit includes a third amplifier A3 and a resistor network. The resistor network is electrically connected to the inverting input terminal and the non-inverting input terminal of the third amplifier A3, and is also electrically connected to the output terminals of the first input amplifier A1 and the second input amplifier A2, respectively, to convert the differential signals output by the first input amplifier A1 and the second input amplifier A2 into the output signal Vo at the sensor output port. The active protection drive circuit includes a protection drive amplifier A4. The input terminal of the protection drive amplifier A4 is electrically connected to the output terminal of the first input amplifier A1 to obtain a drive signal corresponding to the sensor input signal. The output terminal of the protection drive amplifier A4 is electrically connected to the shielding layer of the signal transmission line to drive the potential of the shielding layer to follow the drive signal. In practical implementation, the core amplification circuit of the instrument includes an input buffer circuit and a differential amplifier circuit. The input buffer circuit includes a first input amplifier A1 and a second input amplifier A2. The input terminal of the first input amplifier A1 is electrically connected to the first signal terminal of the sensor input port, and the input terminal of the second input amplifier A2 is electrically connected to the second signal terminal of the sensor input port. By placing A1 and A2 after the sensor input port, the sensor output signal can obtain high input impedance buffer isolation before entering the subsequent processing stage, thereby reducing the loading effect of the subsequent circuit on the high-impedance sensor and providing a low output impedance drive source for subsequent differential processing.

[0033] Here, the differential amplifier circuit includes a third amplifier A3 and a resistor network. The resistor network is electrically connected to the inverting and non-inverting input terminals of the third amplifier A3, and also electrically connected to the output terminals of the first input amplifier A1 and the second input amplifier A2, respectively. This resistor network performs differential amplification and common-mode rejection processing on the signals output from A1 and A2, thereby converting the differential signals output from A1 and A2 into a single-ended output signal Vo at the sensor output port. Through the resistor network's configuration, the third amplifier A3 can achieve differential gain while suppressing common-mode interference, making the output signal Vo more suitable for subsequent acquisition and processing.

[0034] Furthermore, the structure with active protection drive also includes an active protection drive circuit. The active protection drive circuit includes a protection drive amplifier A4, the input terminal of which is electrically connected to the output terminal of the first input amplifier A1 to obtain a drive signal corresponding to the sensor input signal; the output terminal of the protection drive amplifier A4 is electrically connected to the shielding layer of the signal transmission line to drive the potential of the shielding layer to follow the drive signal.

[0035] Here, by making the shielding layer potential change with the signal core potential, the equivalent potential difference between the signal core and the shielding layer can be reduced, thereby suppressing the displacement current generated by the distributed capacitance between the signal core and the shielding layer, reducing the shunting effect of parasitic capacitance on the high-impedance sensor signal, and thus improving the bandwidth limitation problem.

[0036] It should be noted that both the first input amplifier A1 and the second input amplifier A2 are configured as voltage follower structures, with their outputs directly fed back to their respective inverting inputs, and their non-inverting inputs forming the first and second signal terminals of the sensor input port, respectively. The key advantage of this structure lies in its extremely high input impedance (typically exceeding 10^9 Ω) and extremely low input bias current, ensuring that signals can be drawn from high-impedance sensors without significant signal attenuation.

[0037] Furthermore, the signal transmission line includes a signal core and a shielding layer (i.e., the cable shielding layer in the figure); the signal core is electrically connected to the sensor input port and connected to the first input amplifier or the second input amplifier; the shielding layer is electrically connected to the output terminal of the protection drive amplifier so that the potential of the shielding layer follows the potential of the signal core, thereby reducing the equivalent potential difference between the signal core and the shielding layer.

[0038] Here, the signal core is electrically connected to the sensor input port and connected to either the first input amplifier A1 or the second input amplifier A2 to transmit and introduce the sensor input signal. The shielding layer is electrically connected to the output of the protection drive amplifier A4, and is used to make the potential of the shielding layer change with the potential of the signal core under the driving action of the protection drive amplifier A4.

[0039] In this way, since the potential of the shielding layer follows the potential of the signal core, the potential difference between the signal core and the shielding layer is reduced, thereby reducing the displacement current generated by the equivalent distributed capacitance between the two, suppressing the shunting effect of parasitic capacitance on the sensor input signal, reducing the bandwidth limitation and waveform distortion risk of high impedance sensors in the signal transmission process, and improving the measurement capability of dynamically changing signals.

[0040] Optionally, the shielding layer can be replaced with an independent protective conductor; the independent protective conductor is laid along the signal core and electrically connected to the output of the protective drive amplifier to neutralize the parasitic capacitance around the signal core.

[0041] Here, the shielding layer can be replaced with an independent protective conductor. The independent protective conductor is laid along the signal core and electrically connected to the output terminal of the protective drive amplifier A4, so that the potential of the independent protective conductor changes with the potential change of the signal core under the drive of the protective drive amplifier A4.

[0042] It should be noted that the input sampling point of the protection drive amplifier A4 is the output terminal of the first input amplifier A1, and the output terminal of the protection drive amplifier A4 drives the shielding layer so that the potential of the shielding layer is equal to the output potential of the first input amplifier A1. A4 drives the cable shielding layer to a potential that is approximately equal to the output of A1 (i.e., the signal line). The voltage difference between the signal line and the shielding layer is approximately 0, thereby eliminating the influence of C_stray (cable distributed capacitance).

[0043] In this way, by placing an independent protective conductor around the signal core and driving it with a potential follower, the equivalent potential difference between the signal core and the independent protective conductor can be reduced, thereby reducing the displacement current caused by the parasitic capacitance around the signal core, achieving a bootstrap neutralization effect on the parasitic capacitance, reducing the shunting and bandwidth limitation of the parasitic capacitance on the high-impedance sensor signal, and improving the dynamic response capability and measurement stability of the signal transmission and amplification process.

[0044] As one possible implementation, the input buffer circuit also includes a gain setting impedance, which is connected between the output terminal of the first input amplifier A1 and the output terminal of the second input amplifier A2, and is used to set the differential gain of the front stage of the instrumentation amplification core circuit; the gain setting impedance is a gain setting resistor Rg, one end of which is electrically connected to the output terminal of the first input amplifier A1 and the other end of which is electrically connected to the output terminal of the second input amplifier A2.

[0045] In this way, by introducing a gain setting resistor Rg between the output terminals of A1 and A2, A1 and A2 can form a pre-amplifier structure with adjustable differential gain. The differential gain of the pre-amplifier changes with the resistance value of the gain setting resistor Rg, thereby achieving overall gain adjustment without changing the differential amplifier circuit structure. This facilitates matching settings based on the output amplitude of different high-impedance sensors and the acquisition range of the subsequent stage, and improves the applicability and debugging convenience of the system.

[0046] As another possible implementation, the resistor network includes a first resistor R1, a second resistor R2, a third resistor R3, and a fourth resistor R4; the first resistor R1 and the second resistor R2 are matching resistors, and the third resistor R3 and the fourth resistor R4 are matching resistors; the inverting input terminal of the third amplifier A3 is electrically connected to the output terminal of the first input amplifier A1 via the first resistor R1, and is electrically connected to the sensor output port via the third resistor R3; the non-inverting input terminal of the third amplifier A3 is electrically connected to the output terminal of the second input amplifier A2 via the second resistor R2, and is electrically connected to the reference potential terminal via the fourth resistor R4.

[0047] Here, through the above connection method, the differential signals output by A1 and A2 are introduced to the inverting input terminal and the non-inverting input terminal of A3 via R1 and R2 respectively. Under the feedback effect of R3, A3 amplifies the differential component and outputs it to the sensor output port. At the same time, the non-inverting input terminal is connected to the reference potential terminal via R4 to determine the output reference potential. Furthermore, by utilizing the matching relationship between R1 and R2, and R3 and R4, the common-mode conversion error caused by resistor mismatch can be reduced, thereby improving the differential amplification accuracy and common-mode rejection performance, making the output signal more stable and more suitable for subsequent acquisition and processing.

[0048] Preferably, the first resistor R1 and the second resistor R2 are set to have the same resistance value, the third resistor R3 and the fourth resistor R4 are set to have the same resistance value, and the gain of the third amplifier A3 is determined by the resistance ratio R3 / R1.

[0049] Further, see Figure 3 The diagram shown is a circuit schematic of another instrumentation amplifier with active protection drive provided in an embodiment of this disclosure.

[0050] exist Figure 1-2 On the basis of, such as Figure 3 As shown, the protection driver amplifier A4 is configured as a unity-gain buffer A_G. The output of the unity-gain buffer A_G is fed back to the inverting input, and the non-inverting input constitutes the input of the unity-gain buffer A_G. A phase compensation network is also provided, which is set in the feedback loop of the protection driver amplifier A4 to compensate for the loop phase when the protection driver amplifier A4 drives a capacitive load. The phase compensation network includes a compensation capacitor Cf, which is connected in parallel between the output of the unity-gain buffer A_G and the inverting input. The compensation capacitor Cf is an adjustable capacitor used to adjust the trade-off between stability margin and bandwidth when the cable length or parasitic capacitance changes. An isolation resistor Ro is connected in series between the input of the unity-gain buffer A_G and the output of the first input amplifier A1 to reduce the load coupling of the active protection drive circuit to the output of the first input amplifier A1.

[0051] In practical implementation, the protection driver amplifier A4 is configured as a unity-gain buffer A_G. The unity-gain buffer A_G adopts a voltage follower topology, with its output terminal fed back to the inverting input terminal, and its non-inverting input terminal forming the input terminal of the unity-gain buffer A_G. This allows the unity-gain buffer A_G to replicate its input potential with unity gain and drive the output with low output impedance.

[0052] Specifically, to ensure the stability of the protection driver amplifier A4 when driving the capacitive load of the shielding layer, a phase compensation network is also included in the circuit. This phase compensation network is located in the feedback loop of the protection driver amplifier A4 and is used to compensate for the loop phase when the amplifier drives the capacitive load. This reduces the risk of ringing or oscillation caused by high-frequency phase lag, thereby maintaining the stable operation of the active protection drive loop under different cable lengths and parasitic capacitance conditions, while also considering stability margin and measurement bandwidth.

[0053] Here, by connecting the output of the unity-gain buffer A_G to the shielding layer or protective conductor of the signal transmission line, the potential of the shielding layer / protective conductor can be driven to follow the change of the signal core potential, thereby reducing the equivalent potential difference between the signal core and the shielding layer / protective conductor, reducing the displacement current caused by distributed capacitance, thereby weakening the shunting effect of parasitic capacitance on the high-impedance sensor signal and improving the system bandwidth.

[0054] Furthermore, the phase compensation network includes a compensation capacitor Cf, which is connected in parallel between the output terminal and the inverting input terminal of the unity-gain buffer A_G, that is, it is set in parallel in the feedback loop of the unity-gain buffer A_G.

[0055] When the unity-gain buffer A_G drives a capacitive load such as the cable shield, the capacitive load and the amplifier's own frequency characteristics can easily introduce additional phase lag, which can lead to a decrease in loop stability margin and the risk of ringing or oscillation. By setting a compensation capacitor Cf in parallel, a controlled frequency compensation effect can be introduced into the feedback loop to compensate for the loop phase when the unity-gain buffer A_G drives a capacitive load, thereby improving high-frequency stability.

[0056] Preferably, the compensation capacitor Cf is an adjustable capacitor, so that when the capacitive load is different due to changes in cable length or parasitic capacitance, the capacitance of Cf can be adjusted to achieve a trade-off between stability margin and bandwidth, so as to extend the effective measurement bandwidth as much as possible while ensuring no ringing / oscillation.

[0057] Furthermore, to reduce the coupling effect of the active protection drive branch on the preceding signal, an isolation resistor Ro is connected in series between the input of the unity-gain buffer A_G and the output of the first input amplifier A1. The isolation resistor Ro provides impedance isolation to the input branch of the active protection drive circuit, making it less likely that dynamic load changes at the input of the unity-gain buffer A_G will be directly coupled to the output of the first input amplifier A1. This reduces the impact of the active protection drive circuit on the load disturbance and stability of the A1 output, improving the overall reliability and adjustability of the system.

[0058] In practical operation, the input of the active protection drive circuit is directly connected to the output of the first input amplifier A1. Therefore, it can acquire a voltage signal in real time that is highly correlated with the sensor signal amplitude and has undergone preliminary buffering. This signal is fed into a dedicated unity-gain buffer A_G. A_G is designed as a high-output-current, high-slew-rate, high-bandwidth operational amplifier configured as a voltage follower; its core task is to accurately reproduce its input voltage with extremely low output impedance. The output of A_G is directly connected to the shielding layer of the sensor signal transmission cable or a separate protective conductor.

[0059] Here, when the A_G drives the capacitive load of the cable shield, additional phase hysteresis is generated. Simultaneously, the op-amp itself exhibits phase shift at high frequencies. The superposition of these phase shifts may cause the loop to meet the oscillation condition at a certain high-frequency point. The capacitor Cf, together with the inherent output impedance Ro of the A_G, introduces a controllable dominant pole in the feedback loop. This pole actively reduces the loop gain at a slope of -20dB / decimal frequency before the frequency region where the gain is excessively high and the phase shift is dangerous, thus ensuring that the loop gain has dropped below 1 when the total phase shift reaches 180°, thus breaking the oscillation condition. The capacitor Cf is designed to be adjustable (e.g., 2-20pF), allowing circuit designers to finely adjust the value of Cf on the final PCB by observing the output waveform to achieve the optimal balance between system stability and bandwidth, eliminating any potential high-frequency ringing or oscillation.

[0060] Ideally, since the output voltage of A_G is infinitely close to the output voltage of A1 (i.e., the potential of the signal core), the potential difference between them is ΔV≈0. According to the capacitor current formula I=C_s*d(ΔV) / dt, since ΔV≈0, the displacement current I flowing through the distributed capacitance C_s is approximately 0. From the perspective of the AC model, this is equivalent to raising the impedance of the parasitic capacitance C_s to near infinity, so that it no longer shunts the high-frequency components of the input signal.

[0061] Therefore, the low-pass filter model that limits bandwidth, consisting of sensor resistance Rs and parasitic capacitance Cp, is effectively broken down, allowing high-frequency components of the signal to pass through without attenuation, thereby increasing the system bandwidth by orders of magnitude.

[0062] This disclosure provides an instrumentation amplifier with active protection drive. By introducing an active protection drive circuit outside the core circuit of the instrumentation amplifier, the potential of the signal transmission line shielding layer follows the output potential of the input buffer circuit, thereby reducing the equivalent potential difference between the signal core and the shielding layer, reducing the shunting effect caused by parasitic capacitance, and thus improving the effective bandwidth of the high-impedance sensor measurement system. At the same time, a phase compensation network is set in the feedback loop of the protection drive amplifier to compensate for the loop phase when driving capacitive loads, which can suppress ringing and oscillation, improve system stability and signal-to-noise ratio, and enhance the applicability and adjustability of the circuit under different cable lengths and parasitic capacitance conditions.

[0063] Finally, it should be noted that the above-described embodiments are merely specific implementations of this disclosure, used to illustrate the technical solutions of this disclosure, and not to limit it. The protection scope of this disclosure is not limited thereto. Although this disclosure has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features, within the scope of the technology disclosed in this disclosure. Such modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this disclosure, and should all be covered within the protection scope of this disclosure. Therefore, the protection scope of this disclosure should be determined by the protection scope of the claims.

Claims

1. An instrument amplifier with active protection drive, characterized in that, include: The instrument includes a sensor input port, a sensor output port, a signal transmission line connected to the sensor input port, an instrument amplification core circuit, an active protection drive circuit, and a phase compensation network. The instrument amplification core circuit includes an input buffer circuit and a differential amplifier circuit. The input buffer circuit includes a first input amplifier and a second input amplifier. The input terminal of the first input amplifier is electrically connected to the first signal terminal of the sensor input port, and the input terminal of the second input amplifier is electrically connected to the second signal terminal of the sensor input port. The differential amplifier circuit includes a third amplifier and a resistor network. The resistor network is electrically connected to the inverting input terminal and the non-inverting input terminal of the third amplifier, and is also electrically connected to the output terminals of the first input amplifier and the second input amplifier, respectively, so as to convert the differential signal output by the first input amplifier and the second input amplifier into the output signal at the sensor output port. The active protection drive circuit includes a protection drive amplifier. The input terminal of the protection drive amplifier is electrically connected to the output terminal of the first input amplifier to obtain a drive signal corresponding to the sensor input signal. The output terminal of the protection drive amplifier is electrically connected to the shielding layer of the signal transmission line to drive the potential of the shielding layer to follow the drive signal. The phase compensation network is set in the feedback loop of the protection drive amplifier and is used to compensate the loop phase when the protection drive amplifier drives a capacitive load.

2. The instrument amplifier with active protection drive according to claim 1, characterized in that: Both the first input amplifier and the second input amplifier are configured as voltage follower structures, with their outputs directly fed back to their respective inverting inputs, and their respective non-inverting inputs forming the first signal terminal and the second signal terminal of the sensor input port, respectively.

3. The instrument amplifier with active protection drive according to claim 1, characterized in that: The input buffer circuit also includes a gain setting impedance, which is connected between the output terminal of the first input amplifier and the output terminal of the second input amplifier, and is used to set the differential gain of the front stage of the instrument amplification core circuit. The gain setting impedance is a gain setting resistor, one end of which is electrically connected to the output terminal of the first input amplifier, and the other end is electrically connected to the output terminal of the second input amplifier.

4. The instrument amplifier with active protection drive according to claim 1, characterized in that, The resistor network includes a first resistor, a second resistor, a third resistor, and a fourth resistor; The first resistor and the second resistor are matching resistors, and the third resistor and the fourth resistor are matching resistors; The inverting input terminal of the third amplifier is electrically connected to the output terminal of the first input amplifier via the first resistor, and is also electrically connected to the sensor output port via the third resistor. The non-inverting input terminal of the third amplifier is electrically connected to the output terminal of the second input amplifier via the second resistor, and is electrically connected to the reference potential terminal via the fourth resistor.

5. The instrument amplifier with active protection drive according to claim 1, characterized in that: The protection drive amplifier is configured as a unity-gain buffer; The output of the unity-gain buffer is fed back to the inverting input, and the non-inverting input constitutes the input of the protection drive amplifier.

6. The instrument amplifier with active protection drive according to claim 1, characterized in that: The phase compensation network includes a compensation capacitor, which is connected in parallel between the output terminal and the inverting input terminal of the protection drive amplifier. The compensation capacitor is an adjustable capacitor used to adjust the trade-off between stability margin and bandwidth when the cable length or parasitic capacitance changes.

7. The instrument amplifier with active protection drive according to claim 1, characterized in that: An isolation resistor is connected in series between the input terminal of the protection drive amplifier and the output terminal of the first input amplifier to reduce the load coupling of the active protection drive circuit to the output terminal of the first input amplifier.

8. The instrumentation amplifier with active protection drive according to claim 1, characterized in that: The signal transmission line includes a signal core and a shielding layer; The signal wire core is electrically connected to the sensor input port and connected to the first input amplifier or the second input amplifier; The shielding layer is electrically connected to the output terminal of the protection drive amplifier so that the potential of the shielding layer follows the potential of the signal core, thereby reducing the equivalent potential difference between the signal core and the shielding layer.

9. The instrumentation amplifier with active protection drive according to claim 8, characterized in that: The shielding layer is replaced with an independent protective conductor; The independent protective conductor is laid along the signal core and electrically connected to the output terminal of the protective drive amplifier to perform bootstrap neutralization of the parasitic capacitance around the signal core.

10. The instrumentation amplifier with active protection drive according to claim 8, characterized in that: The input sampling point of the protection drive amplifier is the output terminal of the first input amplifier, and the output terminal of the protection drive amplifier drives the shielding layer so that the potential of the shielding layer is equal to the output potential of the first input amplifier.

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