Current Preamplifiers

The detector output signal is generated by a current preamplifier for photovoltaic detectors, such as InSb, and by a simple detector bias circuit shown in Fig. 4 for photoconductive detectors, such as PbS and Hg Ge. The voltage signal derived from the bias circuit is normally preamplified and forwarded to a phase-sensitive synchronous detector usually embodied in a lock-in amplifier (Stewart, 1970 Blass, 1976b). 

For this procedure usually the tunneling current preamplifier has to be either protected by a special circuit design or disconnected. 

M. Carminati, G. Ferrari, D. Bianchi and M. Sampietro, Femtoampere integrated current preamplifier for low noise and wide bandwidth electrochemistry with nanoelectrodes, Electrochimica Acta, 2013, Vol. in press. 

J. Rosenstein, V. Ray, M. Dmdic and K. L. Shepard, Solid-state nanopores integrated with low-noise preamplifiers for high-bandwidth DNA analysis, Proc. lEEEINIH Life Science Systems and Applications Workshop, 2011, 59-62. G. Ferrari, M. Farina, F. Guagliardo, M. Carminati and M. Sampietro, Ultra-low-noise CMOS current preamplifier from DC to 1 MHz, Electronics Letters, 2009, 1278-1280. 

Where stray currents are involved, several measurements have to be taken that are continually changing with time, simultaneously with each other. A double recorder is most suitable for this. Linear recorders with direct indication of the measurements cannot be used for potential measurements because the torque of the mechanism is too small to overcome the friction of the pen on the paper. Amplified recorders or potentiometer recorders are used to record potentials. In amplified recorders, as in amplified voltmeters, the measured signal is converted into a load-independent impressed current and transmitted to the measuring mechanism, which consists of a torque motor with a preamplifier. The amplifier results in an... 

Fig. 12 (a) Current-distance retraction traces recorded with a goid STM tip for f mM 1,9-nonanedithiol in 1,3,5-trimethyibenzene on Au(lll)-(1 x 1), at bias = 0.10 V. The setpoint current before disabling the feedback was chosen at i0 = 0.1 nA. The retraction rate was 4 nm s-1. (b) Same conditions as in (a), except that the preamplifier iimit was chosen at 10 nA. The dotted lines represent characteristic regions of the low, mid, and high conductances... 

Fig. 13 Plateau count conductance histograms constructed from the plateaus found in the steplike conductance-distance traces for Au-l,9-nonanedithiol-Au junctions, (a) 1,600 selected out of 4,300 traces employing a 1 nA (max) preamplifier (b) 1,100 selected out of 4,300 traces recorded with the 10 nA (max) preamplifier. All other conditions are identical to those in Fig. 12. The insets in (a) and (b) show that the currents within each series scale approximately linearly with the number of peaks [64]...

Figure 3 shows one of our photoacoustic cell for X-ray spectroscopy of solid samples The cylindrical cell has a sample chamber at the center with volume of 0.16 cm which has two windows of beryllium (18 mm x 0.5 mm thickness). A microphone cartridge is commercially available electret type (10 mm ) and the electronics of preamplifier for this microphone is detailed elsewhere Figure 4 shows the typical experimental setup for spectroscopic study X-ray was monochromated by channel cut silicon double crystal (111) and ion chamber was set to monitor the beam intensity. Photoacoustic signal intensity was always divided by the ion chamber current for the normalization against the photon flux. X-ray was modulated by a rotating lead plate (1 mm thick) chopper with two blades. 

Figure 6.2-2 Simplified circuit of an electrochemical STM setup. In addition to the potentiostat (see Figure 6.2.1), an STM preamplifier is added, to which the tip is connected. Ul potentiosta-tic setpoint, U2 tunneling voltage, l(t) tunneling current, U3 = -R l(t).

Ge(Li) Detector Characteristics. Resolution measurements for the 18-cm.8 Ge(Li) detector were made with the anticoincidence shield in the inoperative mode, with a normal operating bias of 1700 volts, and with a preamplifier designed in our Laboratory (3, 4), and operated in conjunction with a Tennelec TC-200 linear amplifier. Resolution at 1.33 M.e.v. was 2.62 k.e.v., FWHM (Figure 4). The electronic pulser resolution for the amplifier system at a slightly lower energy was 1.86 k.e.v., the total capacitance of the detector was 28 pF, the noise slope was 0.035 k.e.v./pF, and the leakage current at 1700 volts was 0.5 X 10"9 amp. 

Many SECM experiments require biasing the substrate. A bipotentiostat in Fig. 1 is used to control both the tip and substrate potentials. Unless transient measurements are made, the response of the bipotentiostat does not have to be fast. More importantly, it should be capable of measuring a broad range of current responses a picoamp scale (or even sub-pA) tip current and a much higher current at a macroscopic substrate. For this reason, it is convenient to have several choices of preamplifiers/current-to-voltage transducers. 

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