Saved in:
| Main Authors: | , , , |
|---|---|
| Format: | Preprint |
| Published: |
2026
|
| Subjects: | |
| Online Access: | https://arxiv.org/abs/2604.18969 |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| _version_ | 1866908982656892928 |
|---|---|
| author | Obo, Hirotaka Tsuchiya, Atsushi Ebihara, Tadashi Wakatsuki, Naoto |
| author_facet | Obo, Hirotaka Tsuchiya, Atsushi Ebihara, Tadashi Wakatsuki, Naoto |
| contents | The self-noise of capacitive sensors, primarily caused by thermal noise from the gate-bias resistor in the preamplifier, imposes a fundamental limit on measurement sensitivity. In electret condenser microphones (ECMs), this resistor simultaneously determines the noise low-pass cutoff frequency and the signal high-pass cutoff frequency through a single RC time constant, creating a trade-off between noise reduction and signal bandwidth. This paper proposes PDS-Amp (Photoelectric DC Servo Amplifier), a circuit technique that replaces the gate-bias resistor with a photoelectric element functioning as an ultra-high-impedance current source. A DC servo loop using lag-lead compensation feeds back the preamplifier output through an LED to control the photocurrent, thereby stabilizing the gate bias while decoupling the noise and signal cutoff frequencies. A custom photosensor based on the external photoelectric effect of a zinc photocathode was fabricated to achieve sub-picoampere dark current, overcoming the limitations of commercial semiconductor photodiodes. Combined with a cascode JFET preamplifier that minimizes input capacitance through bootstrap action, PDS-Amp achieved a self-noise of 11 dBA with a 12 pF dummy microphone. Despite using a small-diameter ECM capsule, this performance is comparable to that of large-diaphragm condenser microphones costing several thousand dollars. Recording experiments with an actual ECM capsule qualitatively confirmed a significant reduction in background noise. The proposed technique is applicable not only to microphones but broadly to capacitive sensors including accelerometers, pressure sensors, and pyroelectric sensors. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2604_18969 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Self-Noise Reduction for Capacitive Sensors via Photoelectric DC Servo: Application to Condenser Microphones Obo, Hirotaka Tsuchiya, Atsushi Ebihara, Tadashi Wakatsuki, Naoto Audio and Speech Processing The self-noise of capacitive sensors, primarily caused by thermal noise from the gate-bias resistor in the preamplifier, imposes a fundamental limit on measurement sensitivity. In electret condenser microphones (ECMs), this resistor simultaneously determines the noise low-pass cutoff frequency and the signal high-pass cutoff frequency through a single RC time constant, creating a trade-off between noise reduction and signal bandwidth. This paper proposes PDS-Amp (Photoelectric DC Servo Amplifier), a circuit technique that replaces the gate-bias resistor with a photoelectric element functioning as an ultra-high-impedance current source. A DC servo loop using lag-lead compensation feeds back the preamplifier output through an LED to control the photocurrent, thereby stabilizing the gate bias while decoupling the noise and signal cutoff frequencies. A custom photosensor based on the external photoelectric effect of a zinc photocathode was fabricated to achieve sub-picoampere dark current, overcoming the limitations of commercial semiconductor photodiodes. Combined with a cascode JFET preamplifier that minimizes input capacitance through bootstrap action, PDS-Amp achieved a self-noise of 11 dBA with a 12 pF dummy microphone. Despite using a small-diameter ECM capsule, this performance is comparable to that of large-diaphragm condenser microphones costing several thousand dollars. Recording experiments with an actual ECM capsule qualitatively confirmed a significant reduction in background noise. The proposed technique is applicable not only to microphones but broadly to capacitive sensors including accelerometers, pressure sensors, and pyroelectric sensors. |
| title | Self-Noise Reduction for Capacitive Sensors via Photoelectric DC Servo: Application to Condenser Microphones |
| topic | Audio and Speech Processing |
| url | https://arxiv.org/abs/2604.18969 |