High dynamic range weak alternating signal extraction circuit under direct current bias background
By combining multi-stage instrumentation amplifiers and low-pass filters, the problem of extracting weak AC signals under strong DC bias was solved, and signal detection with high dynamic range and high signal-to-noise ratio was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- XI AN JIAOTONG UNIV
- Filing Date
- 2026-04-22
- Publication Date
- 2026-07-14
AI Technical Summary
Traditional signal conditioning circuits struggle to achieve both high gain and dynamic range under strong DC bias, resulting in the inability to detect weak AC signals.
The system employs a multi-stage instrumentation amplifier to progressively cancel DC bias, combined with an active low-pass filter and an adjustable gain amplifier module to amplify weak signals in stages, and is powered by a modular low-noise power supply.
Successfully extracted a 50μV AC signal without saturation under a 0.5V DC bias, improving the signal-to-noise ratio and extraction accuracy, and adapting to the input range of the analog-to-digital converter.
Smart Images
Figure CN122394516A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of weak signal acquisition technology, and in particular to a high dynamic range weak AC signal extraction circuit under strong DC bias. Background Technology
[0002] In fields such as biomedical electronics and industrial sensor detection, the signals output by sensors often contain a large DC component (DC bias) and an extremely weak AC useful signal (AC signal). For example, some flexible or electrochemical sensors generate a DC baseline of 0V-0.5V or even higher during operation, while the amplitude of the dynamic change signal to be detected is only about 50μV.
[0003] Traditional signal conditioning circuits often face a trade-off between high gain and dynamic range. If a high-gain amplification is used directly in the first stage, a large DC bias will be amplified simultaneously, causing the amplifier output to saturate instantaneously at the power rail, making it impossible to detect weak AC signals. Summary of the Invention
[0004] Therefore, it is necessary to provide a high dynamic range weak AC signal extraction circuit under strong DC bias background to address the above-mentioned technical problems.
[0005] The following technical solution is adopted in this specification: This specification provides a high dynamic range weak AC signal extraction circuit under strong DC bias background, including: a first-stage instrumentation amplifier, a second-stage instrumentation amplifier, an active low-pass filter, and an adjustable gain amplifier module; The first-stage instrumentation amplifier receives the sensor's output signal and introduces a reverse DC compensation voltage at the Ref pin to cancel out most of the DC component in the sensor's output signal. The second-stage instrumentation amplifier receives the output signal from the first-stage instrumentation amplifier and uses its Ref pin to fine-tune the output signal of the first-stage instrumentation amplifier to ensure that the output signal swing is in the optimal linear region. An active low-pass filter is used to filter out high-frequency noise and environmental power frequency interference introduced during the amplification of the output signal by the second-stage instrumentation amplifier, and obtain a filtered signal. The adjustable gain amplifier module is used to amplify the filtered signal to the target level, resulting in a weak AC signal after voltage amplification.
[0006] Optionally, the amplification factor of the first-stage instrumentation amplifier is 5-10 times, and the amplification factor of the second-stage instrumentation amplifier is 100-500 times.
[0007] Optionally, both the first-stage and second-stage instrumentation amplifiers have their Ref pins connected to a reference voltage and bias module. The reference voltage and bias module is a voltage follower formed by a potentiometer and an OPA188 operational amplifier. The two fixed terminals of the potentiometer are connected to the positive and negative power supplies of the circuit, respectively, and the sliding resistor terminal of the potentiometer is connected to the non-inverting input terminal of the OPA188 operational amplifier. The voltage at the sliding resistor terminal of the potentiometer is the DC compensation voltage input to the corresponding instrumentation amplifier Ref pin.
[0008] Optionally, the output voltage of the sensor's output signal after passing through the first-stage instrumentation amplifier and the second-stage instrumentation amplifier. The calculation formula is: in, This is the gain of the first-stage instrumentation amplifier. This is the gain of the second-stage instrumentation amplifier. This is the positive input terminal of the first-stage instrumentation amplifier. This is the negative input terminal of the first-stage instrumentation amplifier. This is the reference voltage for the first-stage instrumentation amplifier. This is the reference voltage for the second-stage instrumentation amplifier.
[0009] Optionally, the active low-pass filter is a second-order low-pass filter, which is powered by a bipolar power conversion circuit, and the filtered signal is a bipolar signal.
[0010] Optionally, the adjustable gain amplifier module is a non-inverting amplifier composed of an OPA188 operational amplifier and a high-precision resistor network; The adjustable gain amplifier module is used to convert the filtered signal to the target level to match the input range of the back-end analog-to-digital converter.
[0011] Optionally, the circuit also includes a modular low-noise power supply for powering the entire circuit.
[0012] The above-mentioned technical solutions adopted in this specification can achieve the following beneficial effects: In the high dynamic range weak AC signal extraction circuit under strong DC bias provided in this specification, the circuit utilizes the Ref pin of the instrumentation amplifier for step-by-step DC cancellation and adopts a multi-stage cascaded structure to distribute the total gain across two stages, reducing the bandwidth limitation and noise accumulation of a single stage. Combined with low-pass filtering, it significantly improves the signal-to-noise ratio and successfully solves the problem of extracting a 50μV AC signal under a 0.5V DC bias without saturation, thus improving the extraction accuracy of high dynamic range weak AC signals under strong DC bias. Attached Figure Description
[0013] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:
[0014] Figure 1 This is a schematic diagram of a high dynamic range weak AC signal extraction circuit under strong DC bias background provided in this specification. Figure 2 This specification provides a detailed structural diagram of a first-stage instrumentation amplifier and a reference voltage generation circuit; Figure 3 This specification provides a schematic diagram of a second-stage instrumentation amplifier and a reference voltage generation circuit. Figure 4 This specification provides a schematic diagram of the circuit structure of an active low-pass filter. Figure 5 This is a circuit diagram of an adjustable gain amplifier module provided in this specification. Figure 6 This specification provides a circuit diagram of an input power supply EMI filter stage. Figure 7 This is a structural diagram of a positive voltage generation circuit provided in this specification; Figure 8 This is a structural diagram of a negative voltage generation circuit provided in this specification; Figure 9 This specification provides a structural diagram of a precision output circuit for a positive power supply. Figure 10 This is a structural diagram of a precision output circuit for a negative power supply provided in this specification.
[0015] Explanation of reference numerals in the attached figures: 101. First-stage instrumentation amplifier; 102. Second-stage instrumentation amplifier; 103. Active low-pass filter; 104. Adjustable gain amplifier module; 105. Modular low-noise power supply. Detailed Implementation
[0016] To make the objectives, technical solutions, and advantages of this specification clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments in this specification without creative effort are within the scope of protection of this application.
[0017] Existing technologies typically employ the following two methods to process sensor output signals: 1. High-pass filter (DC blocking capacitor) coupling: A capacitor is connected in series at the input of the amplifier.
[0018] Disadvantages: Capacitors filter out low-frequency information, making them unsuitable for applications that require monitoring quasi-static or extremely low-frequency signals; and large capacitors can slow down the circuit response time.
[0019] 2. Differential subtraction circuit: A subtractor is constructed using a common operational amplifier to subtract a fixed DC voltage.
[0020] Disadvantages: It requires extremely high resistor matching accuracy, has a low common-mode rejection ratio (CMRR), and is difficult to accurately cancel 0.5V fluctuations while retaining a 50μV signal. Furthermore, its noise performance is generally inferior to that of dedicated instrumentation amplifiers.
[0021] To address the problem in existing technologies that cannot extract extremely weak AC signals (50μV level) from a large DC bias (0-0.5V) with high signal-to-noise ratio while preserving low-frequency components and preventing amplifier saturation, this invention aims to design a circuit that uses multi-stage instrumentation amplifiers to progressively cancel the DC bias and amplify the signal in stages, combined with subsequent filtering and amplitude adjustment, to achieve accurate extraction of weak signals and adaptation to an analog-to-digital converter (ADC).
[0022] The technical solutions provided by the various embodiments of this application are described in detail below with reference to the accompanying drawings.
[0023] Figure 1 This is a circuit diagram of a high dynamic range weak AC signal extraction circuit under a strong DC bias background, which specifically includes: a first-stage instrumentation amplifier 101, a second-stage instrumentation amplifier 102, an active low-pass filter 103, an adjustable gain amplifier module 104, and a modular low-noise power supply 105. The modular low-noise power supply 105 is used to power the entire circuit.
[0024] The entire circuit is powered by a modular, low-noise power supply with low noise and high stability. Since the target signal is only 50μV, the power supply ripple must be strictly controlled. The power supply module provides clean positive and negative voltage rails to each stage of the operational amplifier and generates a high-precision reference voltage source.
[0025] The first-stage instrumentation amplifier receives the sensor's output signal and introduces a reverse DC compensation voltage at the Ref pin to cancel out most of the DC component in the sensor's output signal.
[0026] The first-stage instrumentation amplifier first performs DC bias coarse adjustment and pre-amplification on the sensor's output signal. The specific principle of the first-stage instrumentation amplifier is as follows: the sensor's output signal (including 0-0.5V DC and weak AC) enters the input terminal of the first-stage instrumentation amplifier. The first-stage instrumentation amplifier is designed with a relatively small amplification factor. Optionally, the amplification factor of the first-stage instrumentation amplifier... The range is 5-10 times to prevent the first-stage output from saturating.
[0027] This invention utilizes the Ref pin (reference / correction pin) of the first-stage instrumentation amplifier to introduce a reverse DC compensation voltage. This voltage, generated by a DAC or precision potentiometer, is used to cancel out most of the DC component (0.5V) in the input signal within the first-stage instrumentation amplifier.
[0028] First-stage instrumentation amplifier output: , This is the output signal of the sensor, which is also the input signal of the first-stage instrumentation amplifier. At this time, the output signal of the first-stage instrumentation amplifier... The DC component in the signal is significantly reduced without distortion.
[0029] The second-stage instrumentation amplifier receives the output signal from the first-stage instrumentation amplifier and uses its Ref pin to fine-tune the output signal of the first-stage instrumentation amplifier to ensure that the output signal swing is in the optimal linear region.
[0030] The second-stage instrumentation amplifier amplifies the output signal of the first-stage instrumentation amplifier with fine amplification and high gain. The principle of the second-stage instrumentation amplifier is as follows: it receives the signal output from the first-stage instrumentation amplifier. Since the DC component has been significantly reduced in the first-stage instrumentation amplifier, this stage can be set with a higher amplification factor. Optionally, the amplification factor of the second-stage instrumentation amplifier... With a range of 100-500x, it focuses on amplifying weak AC signals.
[0031] The function of the second-stage instrumentation amplifier includes: it can also be fine-tuned using its Ref pin to ensure that the output signal swing is in the optimal linear region.
[0032] An active low-pass filter (LPF) is used to filter out high-frequency noise and environmental power frequency interference introduced during the amplification of the output signal by the second-stage instrumentation amplifier, thus obtaining a filtered signal.
[0033] Active low-pass filters can be constructed using precision operational amplifiers, such as Butterworth or Chebyshev filters.
[0034] The principle of an active low-pass filter includes: setting a cutoff frequency to filter out high-frequency noise introduced during the pre-amplification process and environmental power frequency interference, thus ensuring the signal-to-noise ratio (SNR) of the 50μV signal.
[0035] The adjustable gain amplifier module is used to amplify the filtered signal to the target level, resulting in a weak AC signal after voltage amplification.
[0036] The adjustable gain amplifier module is a non-inverting amplifier composed of an OPA188 operational amplifier and a high-precision resistor network. The adjustable gain amplifier module is used to convert the filtered signal (bipolar signal, e.g., ±2V) to the target level (e.g., 0-3.3V or 0-5V) to match the input range of the back-end analog-to-digital converter, ensure full-scale sampling, and improve resolution.
[0037] In one embodiment, such as Figure 2 As shown in the diagram, this embodiment provides a detailed structural diagram of a first-stage instrumentation amplifier and a reference voltage generation circuit. This stage directly interfaces with the sensor, and its task is to extract weak differential signals in a high-noise background and perform preliminary gain amplification and DC bias cancellation.
[0038] Both the first-stage and second-stage instrumentation amplifiers have their Ref pins connected to a reference voltage and bias module. This module, constructed using a potentiometer and an OPA188 operational amplifier, acts as a voltage follower, aiming to generate a low-impedance, adjustable reference voltage. V REF It is used for hardware zeroing or setting the DC operating point; the two fixed terminals of the potentiometer are connected to the positive and negative power supplies of the circuit respectively, and the sliding resistor terminal of the potentiometer is connected to the non-inverting input terminal of the OPA188 operational amplifier. The voltage of the sliding resistor terminal of the potentiometer is the DC compensation voltage input to the Ref pin of the corresponding instrumentation amplifier.
[0039] Core components: Amplifier: AD8422 (Precision Instrument Amplifier).
[0040] Zero-adjustment op-amp: OPA188 (connected as a voltage follower).
[0041] Key resistor: Gain resistor It is a high-precision resistor.
[0042] Zeroing element: Precision multi-turn potentiometer (connected to...) power supply).
[0043] Circuit function and working process: Signal amplification: The weak differential signal from the sensor enters the AD8422. This is due to the settings... This stage provides approximately 19.9 times the gain.
[0044] Hardware zeroing (critical): potentiometer pair A voltage divider is used to generate a regulated voltage. The OPA188 acts as a buffer, outputting this voltage to the REF pin of the AD8422 with extremely low impedance.
[0045] Function: If the sensor has a built-in 50mV DC bias, directly amplifying it by 20 times will result in 1V. By adjusting the potentiometer to apply a reverse voltage to the REF pin, this 1V inherent DC bias voltage (InherentDC Offset) can be pulled back to near 0V at the output of this stage.
[0046] Calculation of the output voltage of the first-stage instrumentation amplifier : in, The reference voltage for the first-stage instrumentation amplifier, i.e., the bias voltage provided by the first-stage hardware zero-adjustment circuit, is set by the potentiometer of the first-stage instrumentation amplifier. This is the positive input terminal of the first-stage instrumentation amplifier. This is the negative input terminal of the first-stage instrumentation amplifier.
[0047] According to the AD8422 chip's datasheet, its voltage gain G and external gain resistor R G The transfer function relationship is as follows: Substituting into the above formula, calculate the gain of the first-stage instrumentation amplifier: like Figure 3 As shown, Figure 3 This is a structural diagram of the second-stage instrumentation amplifier and reference voltage generation circuit. The core principle and working process are the same as those of the first-stage instrumentation amplifier. Gain resistor It is a high-precision resistor.
[0048] Cascade amplification: Receive the output signal of the first-stage instrumentation amplifier Then, it is amplified again by approximately 19.9 times. At this point, the total gain of the two stages reaches... This invention amplifies the original weak signal by approximately 394.4 times through a two-stage instrumentation amplifier design. Compared to a single-stage high-gain amplifier, this balanced distribution avoids the problem of a sharp drop in bandwidth caused by excessive gain in a single-stage amplifier, ensuring the transient response characteristics of the signal.
[0049] Second zeroing: After being amplified by the first-stage instrumentation amplifier, the residual minute DC error is amplified again by a factor of 20 in this stage. Therefore, the second independent OPA188 zero-adjustment circuit is crucial here, as it can finely correct the residual DC drift and ensure that the signal is centered in the linear region before entering the filter.
[0050] Calculation of the output voltage of the second-stage instrumentation amplifier : The reference voltage for the second-stage instrumentation amplifier, i.e., the bias voltage provided by the second-stage hardware zeroing circuit, is independently set by the potentiometer of the second-stage instrumentation amplifier.
[0051] So the actual second-level output is: First-stage instrumentation amplifier output : The output of the instrumentation amplifier is equal to (the input differential signal). (Gain) plus the reference voltage.
[0052] in, The differential input signal of the first-stage instrumentation amplifier (i.e., the sensor signal) ).
[0053] Second-stage instrumentation amplifier input: Single-ended output of the first-stage instrumentation amplifier The input is directly connected to the positive input terminal of the second-stage instrumentation amplifier (the negative input terminal is usually grounded or connected to reference ground). Therefore, the "input" of the second-stage instrumentation amplifier is... .
[0054] Second-stage instrumentation amplifier output : Similarly, according to the instrumentation amplifier formula, the second-stage instrumentation amplifier will amplify (the output of the first-stage instrumentation amplifier) and add the zero-adjustment voltage of the second-stage instrumentation amplifier.
[0055] Substituting into the formula for the first-stage instrumentation amplifier: Will Substitute the expression into the above formula: Final expression The final formula after expansion is: The output voltage of the sensor's output signal after passing through the first-stage instrumentation amplifier and the second-stage instrumentation amplifier The calculation formula is: Interpretation of the physical meaning of the formula: This formula clearly shows the contribution of each part of the voltage in the circuit: This is the useful signal portion, which has been amplified by two gain stages. times (approximately) times).
[0056] This is the effect of the first-stage zero-adjustment voltage. Note that it is also amplified by the second stage. This means that the first-stage zeroing action is very "rough" and sensitive, primarily used to offset most of the sensor's inherent bias.
[0057] This is the effect of the second-stage zero-adjustment voltage. It is not further amplified (it is directly superimposed 1:1), so it provides the ability to finely adjust and correct for the small DC errors remaining after the first-stage amplification, ensuring that the final output is accurately zeroed.
[0058] The active low-pass filter is a second-order low-pass filter. The second-order low-pass filter is powered by a bipolar power conversion circuit, and the filtered signal is a bipolar signal. For example... Figure 4 As shown, Figure 4 This is a schematic diagram of the circuit structure of an active low-pass filter. This stage is used to purify the signal (the output signal of the second-stage instrumentation amplifier), filtering out high-frequency noise (such as power frequency interference and electromagnetic interference), retaining only useful infrasound / low-frequency pressure signals. Core components include:
[0059] Op-amp: OPA188.
[0060] Topology: Second-order Sallen-Key low-pass filter (Unity Gain); due to its dual power supply, this filter can handle bipolar signals and has a larger dynamic margin. This stage also uses OPA188 to construct a Sallen-Key unity-gain topology.
[0061] RC parameters: , .
[0062] Circuit function and working process: Low-pass filter: The cutoff frequency is designed to be very low, specifically for infrasound applications.
[0063] Bipolar processing: Benefiting from Powered by it, it can process positive and negative AC signals without distortion.
[0064] Unity gain: The gain within the passband is 1, neither amplifying nor attenuating the signal amplitude.
[0065] Key performance indicator calculation: Its complex frequency domain transfer function H(s) is: Cutoff frequency : Noise signals above 25.7Hz will be significantly attenuated.
[0066] In this dual-power supply architecture, the filter not only removes high-frequency noise but also transmits negative voltage signals (such as the negative potential generated by the reverse deformation of piezoelectric materials) without distortion, which is difficult to achieve directly in a single-power supply system. A quality factor of Q=0.5 ensures good transient response, making it suitable for capturing weak AC signals from sensors momentarily.
[0067] like Figure 5 As shown, Figure 5 This is a schematic diagram of the circuit structure of the adjustable gain amplifier module. This is the last stage, responsible for amplifying the cleaned signal (the output signal of the active low-pass filter) to the optimal range (target level) that the ADC can sample. (Full scale). To ensure long-term gain stability and reduce thermal noise, this stage uses an OPA188 operational amplifier in conjunction with a high-precision resistor network to form a non-inverting amplifier.
[0068] The core components include: Op-amp: OPA188 (connected as a non-inverting amplifier).
[0069] Key resistor: Feedback resistor Input resistance to ground .
[0070] Circuit function and working process Final amplification: Provides an additional 25x gain.
[0071] Impedance matching: The OPA188 has extremely low output impedance, which can strongly drive the sampling capacitor of the ADC and avoid sampling errors.
[0072] Output voltage calculation : Based on the transfer function of the in-phase amplifier, the voltage gain of this stage... The calculation is as follows: This stage provides a precise 25x voltage amplification.
[0073] At this point, the total gain G of the entire weak AC signal extraction circuit System This is the product of the gain of the first two stages of instrumentation and the gain of the final stage. The total gain G of the first two stages is known. Total = 394.4, then the total system gain is:
[0074] This gain configuration (approximately 10,000 times) is well-suited for processing microvolt-level signals.
[0075] We can obtain: The first-stage instrumentation amplifier (U1) and the second-stage instrumentation amplifier (U2) are both AD8422. The operational amplifier used at their REF terminal is an OPA188, which, along with a potentiometer and positive and negative power supplies, generates a bias voltage. This voltage then enters a second-order Salen-Key topology low-pass filter (active low-pass filter) with RC parameters of 62kΩ and 0.1µF. The final stage OPA188 operational amplifier (adjustable gain amplifier module) is used for amplitude modulation and connection to external readout devices such as ADC modules. This two-stage architecture aims to achieve high gain through multi-stage cascading while maintaining a wide linear bandwidth for each stage.
[0076] In one embodiment, a precision power supply system for powering the circuit is provided, namely a modular low-noise power supply. To support the nanovolt-level noise floor requirements of the aforementioned weak AC signal extraction circuit, the power supply adopts a three-stage cascaded architecture of "input power supply EMI filtering -> intermediate voltage conversion stage -> LDO precision regulation," converting the ordinary 12V DC input into an ultra-low noise, high-precision ±5.00V dual-channel power supply. Specifically, the LTM8045MPY_PBF converts the 12V power supply to 5.8V, the MAX1673ESA converts the 5.8V power supply to -5.8V, and then the LT3045EMSE and LT3094EMSE are used to stabilize the ±5.8V voltage at ±5V.
[0077] like Figure 6 As shown, Figure 6 This is a circuit structure diagram of an input power supply EMI filter stage. The core components and performance of this stage are analyzed as follows: Core component: Murata BNX026H01L (SMD Block Type EMIFIL) Device type: Chip-type wideband EMI filter (π-type structure).
[0078] Key performance: Rated voltage / current: 50V DC / 15A. It has an extremely high power margin.
[0079] Filtering range: Attenuation >40dB within the 100kHz to 1GHz frequency band.
[0080] Advantages: Compared to discrete components, its internally integrated feedthrough capacitors and high-frequency inductors can more effectively block high-frequency conducted interference.
[0081] The connection structure and working principle of this level include: An external power supply of 12V DC is introduced through the DC-005 socket. To construct a more complete filtering network, the circuit adopts a multi-stage "LC-Filter-C" structure:
[0082] Pre-filtering: A power inductor LI LPS3015-222MRC (2.2μH) is first connected in series at the positive terminal of the power supply, and a 22μF / 25V ceramic capacitor is connected in parallel to ground at the input terminal (Pin B) of the BNX026H01L. This constitutes the first-stage LC low-pass filter, which mainly suppresses low-frequency ripple and surge.
[0083] Deep filtering: Current then flows into the BNX026H01L. The device's PSG (power ground) and CG (circuit ground) pins are directly grounded (GND) over a large area. Its internal structure completely "absorbs" any residual broadband RF noise.
[0084] Output buffer: The purified power supply is output from the CB pin and then connected in parallel with a 22μF / 25V capacitor to reduce the power supply impedance and provide transient current support for the subsequent circuits.
[0085] In one embodiment, the intermediate voltage conversion stage is a DC / DC pre-regulation stage. This stage is responsible for efficiently converting the 12V voltage (output of the input power supply EMI filter stage) into an intermediate transition voltage (±5.8V), providing sufficient voltage drop margin for the subsequent LDO while also ensuring efficiency. The intermediate voltage conversion stage includes a positive voltage generation circuit and a negative voltage generation circuit.
[0086] like Figure 7 As shown, Figure 7 This is a block diagram of the positive voltage generation circuit, specifically using the Analog Devices LTM8045 μModule. This is a highly integrated DC / DC converter that integrates a controller, power switch, inductor, and diode. In this design, it is configured as a SEPIC (single-ended primary inductor converter) topology with buck-boost functionality.
[0087] The connection structure includes: Input: Connect to a 12V filtered power supply (output of the input power supply EMI filter stage).
[0088] Topology setup: All VOUTM (Vout-) pins of the chip are connected to GND. This is the key connection method to achieve positive voltage output.
[0089] Frequency setting: Connect a 90.9kΩ resistor (R23) to the RT pin to set the switching frequency to 1MHz.
[0090] Feedback setting: The FB pin is connected to the output terminal through resistor R21 (54.9kΩ).
[0091] Output voltage calculation: Calculation basis: LTM8045 datasheet (SEPIC Mode).
[0092] Formula: Reference voltage of feedback pin proportionality coefficient (Corresponding coefficients in the formula).
[0093] Parameter substitution: Feedback resistor The calculation process includes: The theoretical output voltage is approximately +5.8 V. It should be noted that this voltage reserves approximately 0.8 V for the subsequent LT3045 stage, which is a very reasonable design.
[0094] In one embodiment, such as Figure 8 As shown, Figure 8 The diagram shows the structure of the negative voltage generation circuit. Specifically, the negative voltage generation circuit uses a Maxim Integrated MAX1673 charge pump inverter. It generates a negative voltage using the principle of capacitor energy storage. Compared to inductive switching power supplies, it is smaller in size and has no magnetic interference.
[0095] The connection structure of the negative voltage generation circuit includes: Input: Connect to the +5.8V output of the LTM8045 (output of the positive voltage generation circuit).
[0096] Mode selection: When Pin 1 is connected to a high level, it operates in Linear Mode (linear voltage regulation mode), and the output ripple frequency is fixed and easy to filter out.
[0097] Feedback network: A resistor voltage divider structure is adopted, with input resistor R24 = 100kΩ and feedback resistor R25 = 100kΩ.
[0098] Output voltage calculation: Calculation basis: MAX1673 datasheet (Inverter Configuration).
[0099] Principle: The chip maintains the voltage of the FB pin at 0V (virtual ground) by adjusting the internal impedance.
[0100] Parameter substitution: Input voltage (From the previous level) Feedback resistor Input resistance Calculation process: Theoretical output voltage = -5.8 V.
[0101] In one embodiment, the final precision LDO stage utilizes an ultra-low noise LDO to eliminate residual ripple from the preceding switching power supply, generating the final supply voltage. The final precision LDO stage includes a positive power supply precision output circuit and a negative power supply precision output circuit.
[0102] like Figure 9 As shown, Figure 9 This is a block diagram of the positive power supply precision output circuit, built using the Analog Devices LT3045, currently the industry's highest-performing ultra-low noise (0.8μVrms) and ultra-high PSRR (76dB @ 1MHz) linear regulator. It is specifically designed to power noise-sensitive instruments. Specifically, it includes:
[0103] Connection structure: Input: +5.8V (output of the positive voltage generation circuit), pre-filtered by ferrite bead F1.
[0104] Voltage setting: The chip employs a unique precision current source architecture. Connect resistor R22 (49.9kΩ) to ground via the SET pin.
[0105] Noise reduction: A 0.47μF (C36) capacitor is connected in parallel to the SET pin. This not only enables soft start but also greatly bypasses the thermal noise of the reference voltage, ensuring a clean output.
[0106] Output voltage calculation: Calculation basis: LT3045 datasheet (Current Source Reference).
[0107] Principle: A constant precision current is generated inside the chip. The current flows out from the SET pin.
[0108] Parameter substitution: Precision current ( ) Set resistor Calculation process: The final output voltage is approximately +5.00 V.
[0109] like Figure 10 As shown, Figure 10 This is the block diagram of a precision output circuit for the negative power supply. The circuit is built using the Analog Devices LT3094, a complementary negative voltage version of the LT3045. It possesses the same ultra-low noise and high PSRR characteristics, making it particularly suitable for filtering ripple generated by charge pumps. Specifically, it includes:
[0110] Connection structure: Input: -5.8V (output of the negative voltage generation circuit), pre-filtered by ferrite bead F3.
[0111] Voltage setting: Connect resistor R26 (49.9kΩ) to the SET pin. Output voltage calculation: Calculation basis: LT3094 datasheet.
[0112] Principle: The chip's SET pin outputs... Precision current.
[0113] Parameter substitution: Precision current Set resistor Calculation process: The final output voltage is approximately -5.00 V.
[0114] The power conversion process of a modular low-noise power supply: First stage (step-down): The LTM8045 uModule regulator is used to step down the 12V input to an intermediate voltage of +5.8V. The high integration of the LTM8045 significantly reduces the PCB footprint.
[0115] Second stage (inverting): Using the MAX1673 charge pump inverter, the +5.8V mirror is converted to a negative voltage.
[0116] The third stage (precision regulation): The positive power rail uses an LT3045 ultra-low noise LDO to regulate +5.8V to +5V; the negative power rail uses an LT3094 ultra-low noise LDO to regulate -5.8V to -5V.
[0117] The technical advantages are: the core advantage of this power supply solution lies in the ultra-high power supply rejection ratio (PSRR) and extremely low RMS noise (<1uV) provided by the LT3045 / LT3094. RMS By setting the intermediate voltage to +5.8V, the LDO only needs to bear a voltage difference of 0.8V, which ensures that it is in the optimal operating range and minimizes heat dissipation, achieving a balance between "instrument-grade power supply" and "portable low power consumption".
[0118] The advantages of the circuit of this invention include: 1. Weak signal extraction under a large dynamic range: The innovative use of the instrumentation amplifier's Ref pin for step-by-step DC cancellation successfully solves the problem of extracting a 50μV AC signal under a 0.5V DC bias without saturation.
[0119] 2. High precision and low noise: The multi-stage cascaded structure distributes the total gain across two stages, reducing the bandwidth limitation and noise accumulation of a single stage; combined with low-pass filtering, it significantly improves the signal-to-noise ratio.
[0120] 3. Good ADC interface compatibility: The adjustable gain amplifier module at the final stage ensures that the signal can fully utilize the range of the ADC, improving the overall sampling accuracy of the system.
[0121] Modular design: Each stage of the circuit functions independently, which facilitates debugging and adjustment of gain parameters according to the characteristics of different sensors.
[0122] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
Claims
1. A high dynamic range weak AC signal extraction circuit under strong DC bias, characterized in that, include: First-stage instrumentation amplifier, second-stage instrumentation amplifier, active low-pass filter, and adjustable gain amplifier module; The first-stage instrumentation amplifier receives the sensor's output signal and introduces a reverse DC compensation voltage at the Ref pin to cancel out most of the DC component in the sensor's output signal. The second-stage instrumentation amplifier receives the output signal from the first-stage instrumentation amplifier and uses its Ref pin to fine-tune the output signal of the first-stage instrumentation amplifier to ensure that the output signal swing is in the optimal linear region. An active low-pass filter is used to filter out high-frequency noise and environmental power frequency interference introduced during the amplification of the output signal by the second-stage instrumentation amplifier, and obtain a filtered signal. The adjustable gain amplifier module is used to amplify the filtered signal to the target level, resulting in a weak AC signal after voltage amplification.
2. The circuit according to claim 1, characterized in that, The amplification factor of the first-stage instrumentation amplifier ranges from 5 to 10 times, and the amplification factor of the second-stage instrumentation amplifier ranges from 100 to 500 times.
3. The circuit according to claim 1, characterized in that, The Ref pins of both the first-stage and second-stage instrumentation amplifiers are connected to a reference voltage and bias module. The reference voltage and bias module is a voltage follower formed by a potentiometer and an OPA188 operational amplifier. The two fixed terminals of the potentiometer are connected to the positive and negative power supplies of the circuit, respectively, and the sliding resistor terminal of the potentiometer is connected to the non-inverting input terminal of the OPA188 operational amplifier. The voltage at the sliding resistor terminal of the potentiometer is the DC compensation voltage input to the corresponding Ref pin of the instrumentation amplifier.
4. The circuit according to claim 3, characterized in that, The output voltage of the sensor's output signal after passing through the first-stage instrumentation amplifier and the second-stage instrumentation amplifier The calculation formula is: in, This is the gain of the first-stage instrumentation amplifier. This is the gain of the second-stage instrumentation amplifier. This is the positive input terminal of the first-stage instrumentation amplifier. This is the negative input terminal of the first-stage instrumentation amplifier. This is the reference voltage for the first-stage instrumentation amplifier. This is the reference voltage for the second-stage instrumentation amplifier.
5. The circuit according to claim 1, characterized in that, The active low-pass filter is a second-order low-pass filter. The second-order low-pass filter is powered by a bipolar power conversion circuit, and the filtered signal is a bipolar signal.
6. The circuit according to claim 5, characterized in that, The adjustable gain amplifier module is a non-inverting amplifier composed of an OPA188 operational amplifier and a high-precision resistor network; The adjustable gain amplifier module is used to convert the filtered signal to the target level to match the input range of the back-end analog-to-digital converter.
7. The circuit according to claim 1, characterized in that, The circuit also includes a modular low-noise power supply, which powers the entire circuit.