A miniature low-noise pre-filtering amplification circuit

Abstract

The utility model relates to a kind of miniature low-noise pre-filtering amplification circuit, including the electrical connection of one-stage low-noise amplification circuit, intermediate stage filter circuit, two-stage amplification circuit and last power push circuit in sequence along signal path;The gain of the one-stage low-noise amplification circuit and the two-stage amplification circuit is adjustable;The intermediate stage filter circuit is active filter, and high-pass cutoff frequency and low-pass cutoff frequency can be independently switched. The miniature low-noise pre-filtering amplification circuit is optimized by multistage decoupling, differential amplification architecture and low-noise device cooperation, and performance breakthrough is realized.

Description

Technical Field

[0001] This utility model belongs to the field of signal measurement technology, specifically relating to a miniature low-noise pre-filter amplifier circuit. Background Technology

[0002] Preamplifiers, as key supporting equipment, and standard hydrophones, as core components of underwater acoustic detection, are widely used in marine surveying, military sonar, and underwater engineering monitoring. When capturing underwater sound using standard hydrophone signals, unwanted noise signals are inevitably introduced. These noises include sensor noise, measuring instrument noise, and other coupling noise. Signal acquisition requires signal amplification, filtering out unwanted interference signals, and further amplification of the useful signal to improve the signal-to-noise ratio. The preamplifier is a crucial influencing factor in this process. Traditional preamplifiers suffer from the following problems:

[0003] 1. Insufficient noise suppression: Power supply ripple, electromagnetic interference and input impedance lead to a decrease in signal-to-noise ratio, especially when amplifying weak signals (such as voltage signals less than 10 μV), noise is significant, requiring high-precision filtering and low-noise amplification circuits;

[0004] 2. Limited functionality: The gain and filtering parameters are fixed, making it unable to adapt to dynamic signal requirements;

[0005] 3. Weak anti-interference capability: It lacks transient voltage protection and is susceptible to electrostatic discharge (ESD) or power fluctuations;

[0006] 4. Size and power consumption contradiction: Existing amplifiers mostly rely on complex circuits and independent modules, which makes it difficult to meet the miniaturization and low power consumption requirements of portable instruments. Utility Model Content

[0007] The technical problem to be solved by this utility model is to provide a miniature low-noise pre-filter amplifier circuit, which achieves a performance breakthrough through multi-stage decoupling, differential amplification architecture and low-noise device synergistic optimization.

[0008] The technical solution of this utility model is to provide a miniature low-noise pre-filter amplifier circuit, including a first-stage low-noise amplifier circuit, an intermediate-stage filter circuit, a second-stage amplifier circuit, and a final-stage power drive circuit that are electrically connected sequentially along the signal path.

[0009] The gains of the first-stage low-noise amplifier circuit and the second-stage amplifier circuit are adjustable;

[0010] The intermediate-stage filter circuit is an active filter, whose high-pass cutoff frequency and low-pass cutoff frequency can be switched independently.

[0011] Preferably, the first-stage low-noise amplifier circuit adopts a differential amplifier circuit structure composed of twin field-effect transistors and operational amplifiers.

[0012] Preferably, the first-stage low-noise amplifier circuit has at least four adjustable gain levels, including 0dB, 10dB, 20dB, and 30dB.

[0013] Preferably, the intermediate stage filter circuit adopts a first-order equivalent filter structure built with a single operational amplifier, and the filter frequency band is changed by switching different capacitance values ​​through a rotary switch.

[0014] Preferably, the high-pass cutoff frequency can be selected from multiple frequency points including 1Hz, 10Hz, 50Hz, 100Hz, 500Hz, 1kHz, 5kHz, 10kHz, 25kHz, 50kHz, 100kHz, and 250kHz.

[0015] Preferably, the low-pass cutoff frequency can be selected from multiple frequency points including 1kHz, 5kHz, 10kHz, 15kHz, 20kHz, 25kHz, 50kHz, 100kHz, 250kHz, 500kHz, 750kHz, and 1MHz.

[0016] Preferably, the secondary amplifier circuit has at least three adjustable gain levels, including 0dB, 10dB, and 20dB.

[0017] Preferably, the final stage power drive circuit adopts a single-supply Class AB amplifier circuit composed of transistors, and its output terminal is connected to an isolation capacitor.

[0018] Preferably, the circuit is powered by a single power supply, using a constant current regulated energy storage power supply, with a power supply voltage not exceeding 30V.

[0019] Furthermore, the total gain of the first-stage low-noise amplifier circuit and the second-stage amplifier circuit can be adjusted within the range of 0dB to 50dB using a combination of speed settings.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] This miniature low-noise preamplifier circuit features small size and easy integration after assembly. It can be battery powered and offers flexible power supply. It uses twin field-effect transistors and operational amplifiers to form the preamplifier, resulting in extremely low noise. It has built-in high-pass and low-pass filters to effectively filter out interference signals other than the useful signal. Secondary amplification and power drive improve the load capacity. The total gain is adjustable, thus ensuring better signal conditioning. Attached Figure Description

[0022] Figure 1 This is a circuit connection block diagram of the present invention.

[0023] Figure 2 This is a schematic diagram of the circuit principle of this utility model.

[0024] Figure 3 for Figure 2 A magnified diagram of a mid-stage low-noise amplifier circuit.

[0025] Figure 4 for Figure 2 Enlarged view of the intermediate stage filter circuit.

[0026] Figure 5 for Figure 2 Enlarged diagram of the intermediate two-stage amplifier circuit and the final stage power driver circuit. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0028] refer to Figure 1 and Figure 2 The miniature low-noise pre-amplifier circuit of this invention comprises four main parts connected sequentially along the signal path: a first-stage low-noise amplifier circuit 1, an intermediate-stage high-pass and low-pass filter circuit 2, a second-stage amplifier circuit 3, and a final-stage power driver circuit 4. The entire circuit is powered by a single power supply, with the supply voltage VCC not exceeding DC 30V.

[0029] The first-stage low-noise amplifier circuit 1 is the first stage for signal input, and its core objective is to achieve low-noise amplification. Its specific components include:

[0030] The core amplification device consists of twin field-effect transistors (not shown separately in the figure) and a low-noise operational amplifier U1. This combination combines the advantages of ultra-high input impedance and low noise of field-effect transistors with the high gain of operational amplifiers.

[0031] The gain adjustment network consists of a rotary switch K1 (a dual-gang multi-position switch comprising K1A and K1B, where K1A and K1B are rotary transistors with positions 2 to 6) and resistors R18, R19, R20, and R21. Resistors R18 and R19 are connected in parallel, and resistors R20 and R21 are also connected in parallel. Different resistor combinations are synchronously switched via rotary switch K1, connecting to the feedback loop of operational amplifier U1, thereby changing the closed-loop gain. This gain adjustment network provides four adjustable gain levels: 0dB, 10dB, 20dB, and 30dB.

[0032] Bias circuit: Resistors R5 and R7 are connected in series between VCC and ground. The midpoint of their voltage divider provides a DC bias voltage of 1 / 2 of the power supply voltage to the non-inverting input of operational amplifier U1, ensuring the normal quiescent operating point under single power supply operation.

[0033] The intermediate high-pass and low-pass filter circuit 2 is connected after the first-stage low-noise amplifier circuit 1 and is used to filter out interference outside the signal frequency band. Its specific components include:

[0034] Core filtering device: A first-order active filter is constructed using an operational amplifier U3 as the active device.

[0035] The high-pass filter (HPF) channel is composed of a current-limiting resistor R23 and a high-pass capacitor selection network connected in series. The high-pass capacitor selection network is controlled by a 12-position high-pass selection switch K2, connecting different capacitors (C1-C12) to form a first-order high-pass filter with cutoff frequencies of 1Hz, 10Hz, 50Hz, 100Hz, 500Hz, 1kHz, 5kHz, 10kHz, 25kHz, 50kHz, 100kHz, and 250kHz.

[0036] Low-pass filter (LPF) channel: Consists of resistor R25 and a low-pass capacitor selection network connected in series. The low-pass capacitor selection network is controlled by a 12-position rotary switch K3, connecting different capacitors (C13-C24) to form a first-order low-pass filter with cutoff frequencies of 1kHz, 5kHz, 10kHz, 15kHz, 20kHz, 25kHz, 50kHz, 100kHz, 250kHz, 500kHz, 750kHz, and 1MHz.

[0037] Bias circuit: Resistors R12 and R13 are connected in series to divide the voltage, providing a DC bias of 1 / 2 of the power supply voltage for operational amplifier U3.

[0038] The second-stage amplifier circuit 3 amplifies the filtered, clean signal again. Its specific components include:

[0039] Core amplifier device: Consists of an operational amplifier U2.

[0040] Gain adjustment network: By switching its feedback resistor (which can be achieved through an independent rotary switch or other positions linked to rotary switch K1), it provides three adjustable gain levels of 0dB, 10dB, and 20dB.

[0041] Bias and Coupling: Resistors R32 and R33 are connected in series to divide the voltage, providing bias for operational amplifier U2. The signal is coupled from the filter stage to this stage through capacitor E9.

[0042] The final stage power driver circuit 4 aims to improve the output drive capability and load-driving capability of the signal. Its specific components include:

[0043] Driver structure: A single-supply Class AB amplifier circuit consisting of an NPN transistor Q10 and its base bias resistor, emitter resistor, etc.

[0044] Signal path: The signal amplified by operational amplifier U2 is directly coupled to the base of transistor Q10, and after current amplification by transistor Q10, it is output from its emitter.

[0045] Output isolation: An isolation capacitor E11 is connected in series at the output terminal to block the DC component in the output signal and provide safe AC signal coupling for downstream devices.

[0046] To suppress electromagnetic interference, the entire circuit is fabricated on a printed circuit board and housed in a metal shielded box. In terms of layout, the circuit's signal ground (negative terminal) is connected to the shielded box housing with low impedance. This effectively shields against radiated noise and further improves the signal-to-noise ratio of the entire system.

[0047] The workflow is as follows:

[0048] Input signal → First stage low-noise amplifier circuit (low-noise amplification, coarse gain adjustment) → Intermediate stage high-pass and low-pass filter circuit (bandwidth selection, interference filtering) → Second stage amplifier circuit (signal re-amplification, fine gain adjustment) → Final stage power drive circuit (power boost, load-driven output) → Output signal.

[0049] The following combination Figure 2 , 3 Sections 4 and 5 provide a detailed explanation of the interfaces and connections of each unit circuit:

[0050] 1. Connection of signal input to first-stage low-noise amplifier circuit 1

[0051] The input signal is connected through an input interface (such as a BNC connector), and its positive terminal (Signal+) is directly connected to the gate of the twin field-effect transistor or the non-inverting input terminal (pin 3) of the operational amplifier U1.

[0052] The negative terminal of the input signal (Signal-, i.e., signal ground) is connected to the common ground (GND) of the circuit.

[0053] 2. Connection between the first-stage low-noise amplifier circuit 1 and the intermediate-stage high-pass and low-pass filter circuit 2

[0054] The output point of the first-stage low-noise amplifier circuit 1, namely the output terminal (pin 6) of operational amplifier U1, is directly connected to the input terminal of the intermediate-stage filter circuit through a current-limiting resistor R23.

[0055] This connection point is also the starting point of the high-pass filter channel, that is, the other end of the current-limiting resistor R23 is connected to the common terminal of the high-pass selector switch K2.

[0056] 3. Connection between intermediate high-pass and low-pass filter circuit 2 and secondary amplifier circuit 3

[0057] The output point of the intermediate high-pass and low-pass filter circuit 2, i.e. the output terminal (pin 6) of the operational amplifier U3, is connected to the input terminal of the secondary amplifier circuit 3 through a coupling capacitor E9.

[0058] The input terminal of the second-stage amplifier circuit 3 is specifically the non-inverting input terminal (pin 3) of operational amplifier U2. The coupling capacitor E9 is used to block the DC bias voltage of the preceding stage, allowing only AC signals to pass through.

[0059] 4. Connection between the second-stage amplifier circuit 3 and the final-stage power driver circuit 4

[0060] The output point of the second-stage amplifier circuit 3, namely the output terminal (pin 6) of the operational amplifier U2, is directly coupled to the base of the final stage power driving transistor Q10 through a base resistor.

[0061] This direct coupling method can transmit the complete signal, ensuring the stability of the bias of the Class AB amplifier circuit.

[0062] 5. Connection between the final stage power drive circuit 4 and the signal output.

[0063] The output point of the final stage circuit, namely the emitter of transistor Q10, is connected to the final output interface through an output isolation capacitor E11.

[0064] The other end of the output interface is connected to the circuit common ground (GND). The output isolation capacitor E11 is used to isolate the DC potential of the emitter of transistor Q10, providing a safe AC signal output for subsequent devices.

[0065] 6. Global connections for power supply and bias

[0066] A single power supply (VCC) is connected to the circuit board to power the positive terminals of all operational amplifiers and the collector of transistor Q10.

[0067] The negative power supply terminal (V-, usually pin 4) of all operational amplifiers is connected to common ground (GND).

[0068] Resistors R5 and R7, R12 and R13, and R32 and R33 are connected in series to form a voltage divider, providing a 1 / 2 bias to the power supply voltage for the connected circuit signals. This provides a DC bias voltage of 1 / 2 of the power supply voltage for operational amplifiers U1, U3, and U2, respectively. These bias voltages are injected into the non-inverting input of the op-amps through corresponding resistors (such as R6 and R14), establishing a stable DC operating point for the entire signal path.

[0069] The above description of the connection relationships, combined with the foregoing circuit composition description, completely and clearly defines the hardware implementation method of this utility model.

[0070] In this embodiment, the high-pass filter consists of a first-order filter formed by the current-limiting resistor R23 and the capacitor switched on by the high-pass selection switch K2.

[0071] In this embodiment, the low-pass filter is composed of resistor R25 and the capacitor switched on by rotary switch K3, forming a first-order filter.

[0072] In this embodiment, Qualcomm selector switch K2 and rotary switch K3 are single-pole 12-position rotary switches.

[0073] In this embodiment, resistors R18 and R19, and resistors R20 and R21 are all connected in parallel, with an equivalent resistance of 1454.55R. By switching the combination of rotary switch K1, the connected resistors achieve gain conversion for the first-stage and second-stage amplification.

[0074] This embodiment is suitable for signal processing with a bandwidth of 1MHz.

[0075] In this embodiment, the input impedance is greater than 100MΩ and the output impedance is 10Ω / / 100µF.

[0076] The total gain of this invention is 50dB, divided into six levels. The distribution relationship between the first and second levels is shown in Table 1:

[0077] Table 1. Distribution of six gain levels (Level 1 and Level 2)

[0078]

[0079] This miniature low-noise preamplifier circuit features small size and easy integration after assembly. It can be battery powered and offers flexible power supply. It uses twin field-effect transistors and operational amplifiers to form the preamplifier, resulting in extremely low noise. It has built-in high-pass and low-pass filters to effectively filter out interference signals other than the useful signal. Secondary amplification and power drive improve the load capacity. The total gain is adjustable, thus ensuring better signal conditioning.

Claims

1. A miniature low-noise pre-filter amplifier circuit, characterized in that: It includes a first-stage low-noise amplifier circuit, an intermediate-stage filter circuit, a second-stage amplifier circuit, and a final-stage power drive circuit, which are connected sequentially along the signal path. The gains of the first-stage low-noise amplifier circuit and the second-stage amplifier circuit are adjustable; The intermediate stage filter circuit is an active filter, whose high-pass cutoff frequency and low-pass cutoff frequency can be switched independently. The first-stage low-noise amplifier circuit adopts a differential amplifier circuit structure composed of twin field-effect transistors and operational amplifiers.

2. The miniature low-noise pre-filter amplifier circuit according to claim 1, characterized in that: The first-stage low-noise amplifier circuit has at least four adjustable gain levels, including 0dB, 10dB, 20dB, and 30dB.

3. The miniature low-noise pre-filter amplifier circuit according to claim 1, characterized in that: The intermediate stage filter circuit uses a first-order equivalent filter structure built with a single operational amplifier, and the filter frequency band is changed by switching different capacitance values ​​through a rotary switch.

4. The miniature low-noise pre-filter amplifier circuit according to claim 3, characterized in that: The high-pass cutoff frequency can be selected from multiple frequency points including 1Hz, 10Hz, 50Hz, 100Hz, 500Hz, 1kHz, 5kHz, 10kHz, 25kHz, 50kHz, 100kHz, and 250kHz.

5. The miniature low-noise pre-filter amplifier circuit according to claim 3, characterized in that: The low-pass cutoff frequency can be selected from multiple frequency points including 1kHz, 5kHz, 10kHz, 15kHz, 20kHz, 25kHz, 50kHz, 100kHz, 250kHz, 500kHz, 750kHz, and 1MHz.

6. The miniature low-noise pre-filter amplifier circuit according to claim 1, characterized in that: The secondary amplifier circuit has at least three adjustable gain levels, including 0dB, 10dB, and 20dB.

7. The miniature low-noise pre-filter amplifier circuit according to claim 1, characterized in that: The final stage power drive circuit adopts a single-supply Class AB amplifier circuit composed of transistors, and its output terminal is connected to an isolation capacitor.

8. The miniature low-noise pre-filter amplifier circuit according to claim 1, characterized in that: The circuit is powered by a single power supply with a supply voltage not exceeding 30V.

9. The miniature low-noise pre-filter amplifier circuit according to claim 1, characterized in that: The total gain of the first-stage low-noise amplifier circuit and the second-stage amplifier circuit can be adjusted within the range of 0 dB to 50 dB using a combination of speed settings.

Images