China
Africa
Explore chapters and articles related to this topic
Detectors
Published in C. R. Kitchin, Astrophysical Techniques, 2020
Flicker noise, or 1/f noise, occurs when the signal is modulated in time, either because of its intrinsic variations or because it is being ‘chopped’ or ‘nodded’ (i.e., the source and background or comparison standard are alternately observed). The mechanism of flicker noise is unclear but its amplitude follows an f−n power spectrum where f is the chopping frequency and n lies typically between 0.75 and 2.0. This noise source may obviously be minimised by increasing f. With large arrays of IR detectors now generally available, rapidly chopping between the detector alternately observing an astronomical source and an artificial calibration source is becoming less important, but slower speed nodding between the source and the nearby sky background is still widely needed.
Continuous Wave (CW) Radars
Published in Habibur Rahman, Fundamental Principles of Radar, 2019
The receiver in a simple homodyne CW radar is not as sensitive because of increased flicker noise, which occurs in electronic devices within the radar. The noise power produced by the flicker effect varies with frequency as 1/f. Thus the detector of the CW receiver can introduce a considerable amount of flicker noise resulting in reduced receiver sensitivity. One way to overcome the effects of flicker noise is to amplify the received signal at an intermediate frequency (IF) high enough to render the flicker noise small, and then heterodyne the signal down to lower frequencies. This is achieved by using a simple dual-antenna configuration of the CW radar system shown in Figure 6.3. The receiver of this system is called a superheterodyne receiver. Instead of the usual local oscillator, a portion of the transmitted signal is shifted in frequency by an amount equal to the IF before it is mixed with the received signal. Since the output of the mixer consists of two sidebands on either side of the carrier plus the carrier, a narrow bandpass filter is used to remove all the components except the lower sideband at f0−fIF.
Noise Measurement
Published in John G. Webster, Halit Eren, Measurement, Instrumentation, and Sensors Handbook, 2017
The test circuit of Figure 33.3 can be used to measure the flicker noise coefficient Kf and the flicker noise exponent m. The plot of (vno12¯-vno22)¯ versus frequency for a constant noise bandwidth Δf must be obtained, for example, with a signal analyzer. In the white noise range, the slope of the plot is zero. In the flicker noise range, the slope is −10 dB per decade. The lower frequency at which (vno12¯-vno22)¯ is 3 dB greater than its value in the white noise range is the flicker noise corner frequency ff. It can be shown that
Optimal Sizing of Recycling Folded Cascode Amplifier for Low-Frequency Applications Using New Hybrid Swarm Intelligence-Based Technique
Published in Applied Artificial Intelligence, 2020
Naushad Manzoor Laskar, Koushik Guha, Sourav Nath, K.L. Baishnab, P.K. Paul
The RFC Amplifier is shown in Figure 1. It is a modified version of the conventional folded cascode amplifier (Assad and Martine 2009) and uses the current recycling concept by utilizing previously idle devices in the signal path. This is achieved by splitting the sink transistors M3 and M4 in the ratio of K:1, where K is current gain factor. As a result, gain, slew rate, etc. are considerably improved. Additionally, for improved matching, i.e., to reduce systematic offset two new transistors M11 and M12 as shown in Figure 1. In the circuit, instead of NMOS-based drivers, PMOS-based drivers are better as they offer lower flicker noise (Laskar et al. 2017). Flicker noise is dominant in low frequency and has to be low for minimum noise in low-frequency systems (Du and Odame 2013). Thus, in this work, the amplifier design involves PMOS-based drivers. A more detailed description on the working of this circuit can be studied from Assad and Martine (2009). The total transistors in this circuit is 12 and thus the objective function and hence the problem statement are defined from Equations (1)-(14). The design vector for the problem is shown in Equation (15). The design specifications is shown in Table 1 and the technology constants are the same as shown in Table 2. The channel lengths for different transistors used are: L = 1 µm (for M1a, M1b, M2a, M2b, M6, and M7), L = 1.25 µm (for M3, M4a, M4b, M5a, and M5b), L = 1.5 µm (for M8, M9, M10, and M11), and L = 0.5 µm (for M12 and M13). The problem is thus a seven-dimensional problem and hence solved for minimum circuit are subjected to optimal specifications to be met for use in low frequency applications.