Noise amplifier

Amplifier noise. Can be of two kinds white noise results from random fluctuations of signal over a power spectrum that contains all frequencies equally over a specified bandwidth pink noise results when the frequencies diminish in a specified fashion over a specified range. 

Fume cupboards in themselves generate virtually no noise due to their low air velocities, but they can, and do, amplify noise generated by the exhaust... 

The pulses from an ionization chamber are very small, so that pronounced amplification is required. Also, because the pulses are small, the problem of amplifier noise is acute noise in the early stages of... 

Amplifier noise on large peaks measured via Faraday cups ... 

We are not quite done yet. If we use Eq. (9-47) to compute xe, it requires taking the derivative of x, an exercise that can easily amplify noise. So we want a modified form that allows us to replace this derivative. To begin, we define a new variable... 

For this method, the first derivative of the temperature has to be determined from process measurements with amplified noise filtered out. Since the "safe" temperature need not be specified, the independence and selectivity of this method is greater than with the temperature criterion alone. Another advantage is that a potentially unsafe condition can be identified in its early development stage. However, a number of frequently used, but low hazard thermal processes are characterized by fairly high heating rates, making the use of the first derivative ineffective. 

Such an element provides the high frequency roll-off that is necessary with derivative action (i.e. it avoids the tendency of the ideal derivative mode to amplify noise in the error signal). The inclusion of such an element leads to the transfer function of the relevant industrial controller as being ... 

The derivative (or rate) settings are in units of time and can be adjusted from a few seconds to up to 10 h or more. Because the derivative mode acts on the rate at which the error signal changes, it can also cause unnecessary upsets because, for example, it will react to the sudden set point changes made by the operator. It will also amplify noise, and will cause upsets when the measurement signal changes occur in steps, as in case of periodic measurements. Therefore, in such situations it should either be avoided or the controller be reconfigured so that the D-mode acts only on the measurement and not the error. 

At steady state CC=0, so this system can not control the steady state. Alternatively, it can give a large signal, if the wanted value (Cl) suddenly changes. In this way the system can to some degree overcome the sloppiness created by the integral system or other slow changes in the system. A minus is that this kind of control can create instabilities and amplify noise, so it can not stand alone. 

All signal detectors are required to detect the signal against a background of noise . Therefore, the signal-to-noise ratio must be optimized or, put another way, for maximum sensitivity the noise has to be minimized. The sensitivity of any detector is determined by the noise level in the amplified output signal. In the case of a pyroelectric detector and its associated circuitry, the principal sources of noise are Johnson noise, amplifier noise and thermal fluctuations. 

Fig. 35 Simultaneously measured a,b topography c,d repulsive force e,f a.c. current amplitude on graphite before (a, c, e) and after (b, d, f) Fourier space filtering. The Fourier transform parameters for the inverse transformation of b are taken from the Fourier transformation of e. Scan width 5.5 nm, 500x500 pixel, scan speed 50 nm/s, repulsive force 100 nN, a.c. excitation 3.9 mV at 102 kHz. In order to minimise the piezo amplifier noise, a weak feedback was used and the topography contrast is smaller than 100 pm. Force contrast 1 nN, current contrast from 5.5 to 7 nA...

There are, however, two disadvantages of derivatives. First, they are computationally intense, as a fresh calculation is required for each datapoint in a spectrum or chromatogram. Second, and most importantly, they amplify noise substantially, and, therefore, require low signal to noise ratios. These limitations can be overcome by using Savitsky-Golay coefficients similar to those described in Section 3.3.1.2, which involve rapid calculation of smoothed higher derivatives. The coefficients for a number of window sizes and approximations are presented in Table 3.6. This is a common method for the determination of derivatives and is implemented in many software packages. 

The difficulty is that real spectra always contain noise. Figure 3.25 represents a noisy time series, together with the exponentially filtered data. The filtered time series amplifies noise substantially, which can interfere with signals. Although the peak width of the new transform has indeed decreased, the noise has increased. In addition to making peaks hard to identify, noise also reduces the ability to determine integrals and so concentrations and sometimes to accurately pinpoint peak positions. 

The main disadvantage to repeaters is that they just amplify signals. These signals not only include the network signals, but any noise on the wire as well. Eventually, if you use enough repeaters, you could possibly drown out the signal with the amplified noise. For this reason, repeaters are used only as a temporary fix. 

Readout resolution thermal detector noise dark current and amplifier noise... 

Here, up represents the noise of the photoelectrons. When the photon flux is n, Up x VW up, is the dark current noise of the photomultiplier and is proportional to the dark current itself, up is the flicker noise of the source and is proportional to the signal and uA is the amplifier noise resulting from electronic components. The last contribution can usually be neglected, whereas up is low for very stable sources (e.g., glow discharges) or can be compensated for by simultaneous line and background measurements. As up, x Ip, one should use detectors with low dark current, then the photon noise of the source limits the power of detection. 

The resonance frequency of mixer-amplifier tank circuit is measured to be 1.5 GHz. The SQUID amplifier has the following experimentally measured parameters critical current and normal state resistance per junction of front end SQUID are Ic=40 pA and Rn=4 Q, squid inductance is 40 pH, mutual input inductance is 400 pH and input inductance is 5 nH providing the amplifier noise temperature Tn=90 K. 

UV-to-visible converter, and amplifier noise may affect both the response and the signal-to-nGise characteristics of the detector. 

Many times, in an effort to reduce amplifier noise, capacitors are added across the output of the amplifier, and occasionally at the input (45). These capacitors frequently reduce the response time of the amplifier, which causes a shift in the curve peaks and also a loss of peak resolution. A proper value of capacitor must be used, if noise is a problem, to form a compromise between noise reduction and loss of peak resolution. Amplifier impedance mismatch can also cause nonlinear output voltages, which can distort the curve peaks. 

The procedures described above will work well in the ideal situation, where there is no noise in the data and the X-t curves represent the true conversion profiles so that the derivatives of the curves reveal the true rates. In practice there will be some noise in the raw data, and numerical differentiation notoriously amplifies noise, so that a straightforward application of these procedures is not likely to give satisfactory results. Instead, sophisticated numerical smoothing procedures must be used. The smoothing precedes the procedures presented above and leads to much more stable and accurate results by numerically filtering the data to remove experimental noise. The required filtering procedures are detailed in Chapter 7. 

Most modern X-ray spectrometers (wavelength dispersive as well as energy dispersive) are equipped w itht/fs-criminators that reject pulses of less than about V (after amplification). In this way. transducer and amplifier noise is reduced significantly. Some instruments have puke-height selectors, or u iiuhne iliseriminiitors, which are electronic circuits that reject not only pulses... 

Dark current and amplifier noise Regions where source intensity and... 

The transit time between the absorption of a photon at the photocathode and the output pulse from the anode of a PMT varies from photon to photon. The effeet is called transit time spread", or TTS. There are three major TTS components in conventional PMTs and MCP PMTs - the emission at the photoeathode, the transfer of the photoelectron to the multiplieation system, and the multiplication process in the dynode system or mieroehannel plate. The total transit time jitter in a TCSPC system also contains jitter indueed by amplifier noise and amplitude jitter of the SER. 

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