Structure and system design

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The multi-channel, low-noise integrated readout amplifier for low-frequency small signal voltage sources

The integrated readout amplifier is targeted for high-resistive low-frequency voltage sources. Bandwidth of the amplifier is equal to 3.7kHz, and it starts at 0Hz (DC). The input spectral noise density is virtually constant within this transfer band, and is equal to . This feature – significant reduction of the 1/f noise component is the main advantage of the proposed amplifier. The circuit architecture is based on the well-known chopper amplifier concept and the externally generated chopping (clocking) signal (209kHz) must be provided for proper operation. In general, there are two different gain control mechanisms in the amplifier. First, the gain can be switched (60/80 [dB]) by means of the dedicated 1-bit control signal (0/1). The second possibility, enabling the quasi-linear gain control involves manipulation of the chopping frequency. Designed amplifier can successfully replace the lock-in equipment commonly used in laboratory experiments with several classes of detectors.

All of the features presented above predispose the amplifier to many spectroscopic and imaging applications. Chosen architecture ensures the possibility of parallel merging of the several amplifiers, which results in a complete multichannel readout system. The circuit is fully silicon-proven, its 8-channel version was manufactured in standard 350nm CMOS process in 2014 and successfully tested in the lab. Originally, this amplifier was dedicated to specific detectors, which produce very small output voltage signal (range of tens µV) over the several hundred kilo ohms impedance. According to the design assumptions, only one channel per time was active and available for signal processing. The system can be easily modified, in case of customer need, to provide fully parallel structure with all channels processed simultaneously.

More detailed information about circuit parameters are presented in table and figures below. These results were obtained during the measurements of the fabricated chips and are related to the one, chosen channel of the multichannel structure.



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