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Audio amplifiers
Published in Charlie Cullen, Learn Audio Electronics with Arduino, 2020
To avoid this, the base-emitter voltage (Vbe) of the transistor can be biased to always keep it within the active amplification region. This prevents the BJT from either switching off when the base current becomes negative during the second half of the sine wave cycle or dropping into the saturation region where the transistor is not linear. Biasing involves adding a DC component to the input signal to raise the overall level of the entire signal into the active amplification region (Figure 7.20).
Single-Stage Transistor Amplifiers
Published in Nassir H. Sabah, Electronics, 2017
Concept: The purpose of transistor biasing is to select an appropriate quiescent, or operating, point on the transistor output characteristics, and to stabilize this operating point despite variations in temperature, bias supplies, or transistor parameters, such as βF or Vt, because of manufacturing tolerances. The stabilization entails minimizing the change in output current despite these variations.
Transistors
Published in John Okyere Attia, Circuits and Electronics, 2017
Biasing networks are used to establish an appropriate dc operating point for the transistor in a circuit. For stable and consistent operation, the dc operating point should be held relatively constant under varying conditions. There are several biasing circuits available in the literature. Some are for biasing discrete circuits and others for integrated circuits. Figures 7.17 and 7.18 show some biasing networks for discrete circuits.
Key Components of Rectenna System: A Comprehensive Survey
Published in IETE Journal of Research, 2022
Daasari Surender, Taimoor Khan, Fazal A. Talukdar, Asok De, Yahia M.M. Antar, Al. P. Freundorfer
A rectifier circuit is designed in [41] to operate over a wide range of frequencies. The wideband characteristics are obtained by four rectifier circuits that are designed with non-uniform transmission lines. A differential configuration is designed using a voltage doubler rectifier to improve the conversion efficiency in addition to a stable balanced output voltage [115]. Enhancement in rectenna performance is further noticed with a Greinacher rectifier circuit (GCR) [82, 116–118]. Basically, a Greinacher rectifier circuit is equivalent to a two-stage VDR circuit arranged in a bridge formation. The equivalent circuit arrangement of a GCR is given in Figure 11. The GCR comprising of two branches with two diodes in each branch. The biasing voltage of each diode can be partially produced by the output of the previous diode. In [116], the designed rectifier circuit is suitable to operate over a wide range of frequencies (1.8–2.5 GHz). Whereas in [117], a hybrid rat-race coupler is used to provide the phase difference of 180° to the proposed Greinacher rectifier circuit.
A compact cognitive radio UWB/reconfigurable antenna system with controllable communicating antenna bandwidth
Published in Australian Journal of Electrical and Electronics Engineering, 2019
Abdulghafor Abdulghafar Abdulhameed, Falih Mahdi Alnahwi, Husham Lateef Swadi, Abdulkareem Swadi Abdullah
As mentioned earlier, the communicating antenna is a reconfigurable triangular monopole antenna whose dimensions are illustrated in Figure 2. Two PIN diodes are used to control the antenna centre frequency and bandwidth according to the operational mode of each of them. The PIN diodes used in this work are SMP1320-079LF with forward biasing resistance value of ( at ) and reverse biasing capacitor of (). The PIN diode ON state is simulated by placing resistance equal to the value of the forward biasing resistance, while the reverse biasing capacitance simulates the OFF state of the PIN diode. It is worth to mention that blocking capacitors are not simulated in CST Microwave Studio software
A bulk-driven, buffer-biased, gain-boosted amplifier for biomedical signal enhancement
Published in Cogent Engineering, 2019
Sarin Vijay Mythry, D. Jackuline Moni
In order to design low noise amplifier for biomedical applications, transistor size and biasing are the most important parameters. To estimate the RMS noise of an amplifier, integration of bio-amplifier noise spectral density along with bandwidth is essential. Due to large time constants of integration limits, Rf and Cf in should be considered to be close to zero. The noise displayed at the output of an amplifier is measured as a voltage. The noise is mainly produced by both current and voltage sources. The most widely used specifications for amplifier circuit noise are the IR current and IR voltage noise. These are called IR spectral density function or also called as RMS noise. The V/√Hz is required because of noise power which is added with bandwidth (Hz) or current and voltage noise density will be added with √Hz. The high gain amplifier exhibited only at 1 Hz and still less noise of at 200 Hz. Different noise analyses are depicted in Figure 13, 22, and 23. Figure 22 depicts the squared output noise characteristics of bulk-driven gain-boosted amplifier for biomedical applications. Figure 23 depicts the equivalent output noise characteristics of bulk-driven gain-boosted amplifier for biomedical applications.