Ultralow Noise Low Offset Chopper Amplifier for Induction Coil Sensor to Detect Geomagnetic Field of 1 mHz to 1 kHz

Li, Jiawei; Xi, Zhenzhu; Chen, Xingpeng; He, Wei; Xia, Long; Sheng, Zhou; Wang, Liang

doi:10.32389/jeeg20-014

Cited by 5 publications

(3 citation statements)

References 13 publications

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“…According to Fourier expansion, the modulated square wave

and demodulated square wave

can be calculated as follows [ 19 ]:

…”

Section: Principlesmentioning

confidence: 99%

Ultralow-Noise Chopper Amplifier for Seafloor E-Field Measurement

Song,

Chen

2024

Sensors

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The seafloor E-field signal is extremely weak and difficult to measured, even with a high signal-to-noise ratio. The preamplifier for electrodes is a key technology for ocean-bottom electromagnetic receivers. In this study, a chopper amplifier was proposed and developed to measure the seafloor E-field signal in the nanovolt to millivolt range at significantly low frequencies. It included a modulator, transformer, AC amplifier, high-impedance (hi-Z) module, demodulator, low-pass filter, and chopper clock generator. The injected charge in complementary metal-oxide semiconductor (CMOS) switches that form the modulator is the main source of 1/f noise. Combined with the principles of peak filtering and dead bands, a hi-Z module was designed to effectively reduce low-frequency noise. The chopper amplifier achieved an ultralow voltage noise of 0.6 nV/rt (Hz) at 1 Hz and 1.2 nV/rt (Hz) at 0.001 Hz. The corner frequency was less than 100 mHz, and there were few 1/f noises in the effective observation frequency band used for detecting electric fields. Each component is described with relevant tradeoffs that realize low noise in the low-frequency range. The amplifier was compact, measuring Ø 68 mm × H 12 mm, and had a low power consumption of approximately 23 mW (two channels). The fixed gain was 1500 with an input voltage range of 2.7 mVPP. The chopper amplifiers demonstrated stable performance in offshore geophysical prospecting applications.

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“…According to Fourier expansion, the modulated square wave

and demodulated square wave

can be calculated as follows [ 19 ]:

…”

Section: Principlesmentioning

confidence: 99%

Ultralow-Noise Chopper Amplifier for Seafloor E-Field Measurement

Song,

Chen

2024

Sensors

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show abstract

“…Consequently, the filtering module employs a low-pass filter (LPF) to eliminate a significant portion of the high-frequency noise

and offset

, preserving the low-frequency signal,

, along with a minor fraction of the offset

and noise

. The bandwidth of this LPF [ 26 ] is depicted in Figure 2 c. Figure 2 c,d illustrate the spectral changes before and after signal filtering. Ultimately, the low-frequency and weak signals from the electric field sensor are subject to low-noise amplification following their passage through the filtering module.…”

Section: Chopper Amplifier Circuit Principlementioning

confidence: 99%

“…Consequently, the filtering module employs a low-pass filter (LPF) to eliminate a significant portion of the high-frequency noise v ndm and offset v osdm , preserving the low-frequency signal, Anv i , along with a minor fraction of the offset v osr and noise v nr . The bandwidth of this LPF [26] is depicted in Figure 2c. Figure 2c,d illustrate the spectral changes before and after signal filtering.…”

Section: Chopper Amplifier Circuit Principlementioning

confidence: 99%

A Low-Noise Amplifier for Submarine Electric Field Signal Based on Chopping Amplification Technology

Liu,

Chun,

Chen

et al. 2024

Sensors

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In the exploration of ocean resources, the submarine electric field signal plays a crucial role through marine electromagnetic methods. However, due to the field signal’s low-frequency and weak characteristics, it often encounters interference from the instrument’s own 1/f noise during its acquisition. To address this issue, we developed a low-noise amplifier for the submarine electric field signal based on chopping amplification technology. This amplifier utilizes low-temperature electronic components to adapt to the cold submarine environment and enhances its independence by incorporating a square wave generator. Additionally, we conducted simulations and experimental tests on the designed chopper amplifier circuit, evaluating the equivalent input voltage noise spectrum (EIVNS) and the frequency response within 1 mHz~100 Hz. The experimental results indicate that the amplifier designed in this study achieves sufficiently low noise 2 nV/√Hz@1 mHz, effectively amplifying the submarine electric field signal measured with the electric field sensor.

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Low-noise chopper amplifier design for low-frequency induction magnetometers

Tang,

Xi,

Chen

et al. 2023

Journal of Geophysics and Engineering

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Induction Magnetometers (IM) are commonly used in Magnetotelluric Method for exploration. 1/f noise in the low frequency band of the preamplifier reduce the signal-to-noise ratio of IM, thus affecting the exploration results. We designed a low noise chopper amplifier with equivalent input voltage noise of 9.8 nV/√Hz at 1 mHz, 2.1 nV/√Hz at 0.01 Hz, 1.9 nV/√Hz at 0.1 Hz, 1/f noise corner frequency of 8 mHz, and equivalent input current noise of 200 fA/√Hz at 1 mHz, 100 fA/√Hz at 0.01 Hz, 60 fA/√Hz at 0.1 Hz. The IM using this chopper amplifier is 85.5 cm long, 6.0 cm in diameter and has a total weight of 4.8 kg. Its sensitivity is 300 mV/nT during 20 Hz and 1 kHz, with a theoretical equivalent input magnetic field noise of 0.3 pT/√Hz at 1 Hz and a measurement frequency range of 1 mHz to 1 kHz.

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Ultralow Noise Low Offset Chopper Amplifier for Induction Coil Sensor to Detect Geomagnetic Field of 1 mHz to 1 kHz

Cited by 5 publications

References 13 publications

Ultralow-Noise Chopper Amplifier for Seafloor E-Field Measurement

Ultralow-Noise Chopper Amplifier for Seafloor E-Field Measurement

A Low-Noise Amplifier for Submarine Electric Field Signal Based on Chopping Amplification Technology

Low-noise chopper amplifier design for low-frequency induction magnetometers

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