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Detailed schematic of the low noise amplifier (A 1 ) together with the two identical auxiliary amplifiers (A 2 , A 3 ) required for gain calibration by means of cross correlation measurements. The detailed component list is reported in Table 1.
Source publication
We propose an open loop voltage amplifier topology based on a single JFET front-end for the realization of very low noise voltage amplifiers to be used in the field of low frequency noise measurements. With respect to amplifiers based on differential input stages, a single transistor stage has, among others, the advantage of a lower background nois...
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... order to test the effectiveness of the approach we propose, we designed the system reported in Figure 4 following the guidelines discussed in the previous section. The complete component list is reported in Table 1. ...
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... 1 Figure 4. Detailed schematic of the low noise amplifier (A1) together with the two identical auxiliary amplifiers (A2, A3) required for gain calibration by means of cross correlation measurements. ...
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... The actual prototype that was implemented and used for testing is shown in Figure 5. The yellow line superimposed to the picture represents the wiring that needs to be added to connect the gate of the JFET J1 to the inputs of the amplifiers A2 and A3 as in Figure 4. Removing the yellow connection allowed to test each amplifier independently of the others. ...
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... actual prototype that was implemented and used for testing is shown in Figure 5. The yellow line superimposed to the picture represents the wiring that needs to be added to connect the gate of the JFET J1 to the inputs of the amplifiers A 2 and A 3 as in Figure 4. Removing the yellow connection allowed to test each amplifier independently of the others. ...
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... BNC connectors are used to allow connection from the outputs of the amplifiers (VO1, VO2, and VO3) to the input of the acquisition and elaboration system. Figure 5. Top view of the implementation of the circuit in Figure 4. All components of amplifiers A1 and A2 are labeled with the same names used in Figure 4. ...
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... 5. Top view of the implementation of the circuit in Figure 4. All components of amplifiers A1 and A2 are labeled with the same names used in Figure 4. The yellow path shows the connection that needs to be made to connect the gate of the JFET to the inputs of A2 and A3. ...
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... discussed in [27], QLSA operates very much like a large number of conventional DFT spectrum analyzers all receiving the same input signal, but with each one operating with the same record length but in a different frequency range and, hence, with a different resolution bandwidth. In particular, at higher frequencies, the resolution bandwidth is larger, resulting in time records with shorter duration, while at lower and lower frequencies, the Figure 4. The yellow path shows the connection that needs to be made to connect the gate of the JFET to the inputs of A 2 and A 3 . ...
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... BNC connectors are used to allow connection from the outputs of the amplifiers (VO1, VO2, and VO3) to the input of the acquisition and elaboration system. Figure 5. Top view of the implementation of the circuit in Figure 4. All components of amplifiers A1 and A2 are labeled with the same names used in Figure 4. ...
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... 5. Top view of the implementation of the circuit in Figure 4. All components of amplifiers A1 and A2 are labeled with the same names used in Figure 4. The yellow path shows the connection that needs to be made to connect the gate of the JFET to the inputs of A2 and A3. ...
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... can be verified, the curve is flat, indicating a constant frequency response from 200 mHz up to above 1 kHz, after which the PSD decreases. However, this decrease can be traced back to the low pass filtering effect due to the capacitance at the input of the JFET that, in the passband and in the configuration in Figure 4, is essentially the sum of the gate-to-source and of the gate-to-drain capacitances of the device, in the order of 500 pF. Indeed, an RC low pass filter with R = 50 kΩ (the resistance of the DUT at the input) and C = 500 pF would result in a pole frequency of about 6.4 kHz, consistent with the behavior for S 11 observed in Figure 7. ...
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... can be verified, the curve is flat, indicating a constant frequency response from 200 mHz up to above 1 kHz, after which the PSD decreases. However, this decrease can be traced back to the low pass filtering effect due to the capacitance at the input of the JFET that, in the passband and in the configuration in Figure 4, is essentially the sum of the gate-to-source and of the gate-to-drain capacitances of the device, in the order of 500 pF. Indeed, an RC low pass filter with R = 50 k(the resistance of the DUT at the input) and C = 500 pF would result in a pole frequency of about 6.4 kHz, consistent with the behavior for S11 observed in Figure 7. ...
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... order to obtain very smooth spectra at very low frequencies, averaging for the spectra in Figure 7 was carried on for about 2 h. However, the correct estimate of the gain AV1 was obtained just after a few seconds, as confirmed from the plot of |AV1,M| vs. time in Figure 8a. Figure 7. Cross spectra at the outputs VO1, VO2, and VO3 in Figure 4. The black curves are obtained with RDUT = 50 k; the gray curves refer to the case RDUT = 100 . ...
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... verify the robustness of the approach we propose, the estimation of AV1,M was carried out over two frequency ranges. The circles in Figure 8a are relative to the estimation of the gain performed in the frequency range from 200 Hz to 1 kHz (with f = 6.25 Hz) where the recorded spectra appear to Figure 7. Cross spectra at the outputs V O1 , V O2 , and V O3 in Figure 4. The black curves are obtained with R DUT = 50 kΩ; the gray curves refer to the case R DUT = 100 Ω. S 11 is the power spectral density (PSD) at the output of the low noise amplifier (A 1 ); S 22 is the PSD at the output of one of the auxiliary amplifiers (A 2 ); S 12 is the cross spectrum between the low noise amplifier (A 1 ) and one of the auxiliary amplifiers (A 2 ); S 23 is the cross spectrum between the outputs of the two auxiliary amplifiers. ...
Citations
... However, the fast progress in semiconductors and new materials process technologies often results in the need to develop dedicated instrumentation and new methodologies for noise measurement and analysis [11][12][13]. Obtaining reliable noise characterization is especially challenging in the case of low-resistance DUTs (impedances below 10 Ω), and in these cases it is necessary to resort to a dedicated amplifier design and/or to the application of cross-correlation methods [14,15]. Besides resorting to these solutions, especially in the case of low-resistance DUTs, signal transformers can be used in the measurement chain between the DUT and the preamplifier's input to reduce the system's background noise (BN). ...
When performing low-frequency noise measurements on low-impedance electron devices , transformer coupling can be quite effective in reducing the contribution of the equivalent input noise voltage of the preamplifier to the background noise of the system. However, noise measurements on electron devices are usually performed with a biased device under test. A bridge configuration must be used to null the DC component at the input of the transformer. Unfortunately, using a bridge results in a complication of the setup and degradation of the system's sensitivity because of the noise introduced by the nulling arm. We propose an alternative approach for blocking the DC component that exploits the fact that supercapacitors with capacitances in excess of a few Farads are nowadays easily available. Actual measurement results in conventional and advanced measurement configurations are discussed that demonstrate the advantages of the approach we propose.
... Flicker noise typically increases with bias and needs to overcome the thermal noise to be clearly detected. However, in the case of low impedance devices, it is not the thermal noise of the device that represents the limiting factor in the detection of flicker noise at low frequencies, but rather, the level of the equivalent input noise of the amplifiers that, even when using dedicate instrumentation [13,14], can be as large as a few nV√Hz at frequencies close to 1 Hz. Crosscorrelation approaches can be used to obtain an equivalent background noise that is well below the equivalent voltage noise of the available amplifiers. ...
The paper presents a noise measurement system particularly suited for the investigation of the low frequency noise in advanced infrared (IR) detectors characterized by low shunt resistance. By combining the performances of ultra-low noise amplifiers with the advantages that can be obtained by transformer input coupling and cross-correlation between two nominally identical channels, we were able to obtain excellent noise performances in the low frequency region (below 10 Hz). Indeed, the equivalent input background noise that can be obtained with the approach we propose can be as low as 1×10⁻²⁰ V²/Hz (≈100 pV/√Hz) at 1 Hz. The system was tested using source resistances in the range from 1 to 10 Ω as well as actual advanced IR detectors to demonstrate its ability to provide information about the noise generated at very low frequencies.
... Rather, it is the type of DUT and its characteristics, among which the equivalent impedance plays a major role, that guides the design of the amplifier. Typically, for low impedance DUTs, it is the equivalent voltage noise e n of the amplifier that limits the sensitivity, while the equivalent input current i n is mainly responsible for limiting the sensitivity in the case of high impedance DUTs [17][18][19]. ...
The paper presents a system for noise measurements in infrared photodetectors characterized by low shunt resistances based on a two-channel ultra-low-noise voltage amplifier with paralleled discrete JFETs at the input stages. Using cross correlation method, a background noise well below of 10⁻¹⁹ V²/Hz can be obtained at frequencies above 10 Hz. To facilitate the estimation of the noise in such a wide frequency range (5 decades), we also developed a software based on the QLSA library. As a result of these efforts, the equivalent input voltage noise of the system is below 10⁻¹⁹ V²/Hz at 10 Hz and 10⁻²⁰ V²/Hz for frequencies above a few hundred Hz. The system effectiveness is demonstrated by noise measurements at room temperature on advanced InAsxSb1-x photodetectors characterized by an active area of 1 mm² and a shunt resistance below 10Ω.
... Its noise is around 1.4 nV/ √ Hz and 0.6 nV/ √ Hz for the frequencies of 1 Hz and 10 Hz, respectively. Another interesting design implementing some additional amplifiers characterized by well-known gain and a specific calibration method is described in [34]. There was applied an amplifier input stage with some paralleled transistors. ...
The paper presents a low noise voltage FET amplifier for low frequency noise measurements. It was built using two stages of an op amp transimpedance amplifier. To reduce voltage noise, eight-paralleled low noise discrete JFETs were used in the first stage. The designed amplifier was then compared to commercial ones. Its measured value of voltage noise spectral density is around 24 nV/ √ Hz, 3 nV/ √ Hz, 0.95 nV/ √ Hz and 0.6 nV/ √ Hz at the frequency of 0.1, 1, 10 and 100 Hz, respectively. A −3 dB frequency response is from ∼ 20 mHz to ∼ 600 kHz.
The review includes results of analyses and research aimed at standardizing the concepts and measurement procedures associated with photodetector parameters. Photodetectors are key components that ensure the conversion of incoming optical radiation into an electrical signal in a wide variety of sophisticated optoelectronic systems and everyday devices, such as smartwatches and systems that measure the composition of the Martian atmosphere. Semiconductor detectors are presented, and they play a major role due to their excellent optical and electrical parameters as well as physical parameters, stability, and long mean time to failure. As their performance depends on the manufacturing technology and internal architecture, different types of photodetectors are described first. The following parts of the article concern metrological aspects related to their characterization. All the basic parameters have been defined, which are useful both for their users and their developers. This allows for the verification of photodetectors' workmanship quality, the capabilities of a given technology, and, above all, suitability for a specific application and the performance of the final optoelectronic system. Experimentally validated meteorological models and equivalent diagrams, which are necessary for the correct analysis of parameter measurements, are also presented. The current state of knowledge presented in recognized scientific papers and the results of the authors' works are described as well.
Silicon photomultipliers (SiPMs) offer advantages such as lower relative cost, smaller size, and lower operating voltages compared to photomultiplier tubes. A SiPM’s readout circuit topology can significantly affect the characteristics of an imaging array. In nuclear imaging and detection, energy, timing, and position are the primary characteristics of interest. Nuclear imaging has applications in the medical, astronomy, and high energy physics fields, making SiPMs an active research area. This work is focused on the circuit topologies required for nuclear imaging. We surveyed the readout strategies including the front end preamplification topology choices of transimpedance amplifier, charge amplifier, and voltage amplifier. In addition, a review of circuit topologies suitable for energy, timing, and position information extraction was performed along with a summary of performance limitations and current challenges.
