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Transmitters
Published in Mike Golio, Commercial Wireless Circuits and Components Handbook, 2018
Fixed predistortion methods are conceptually the simplest form of linearization. A power amplifier will have nonlinearities that distort the original signal. By providing complimentary distortion prior to the PA, the predistorted signal is linearized by the PA. The basic concept can be divided into digital and transfer characteristic methods, both with the same objective. In the digital method (Fig. 2.6), digital signal processing (DSP) is used to provide the required predistortion to the signal. This can be applied at any point in the system, but is usually provided at baseband where it can be cheaply accomplished. The information required for predistortion must be determined and then stored in memory. The DSP then utilizes this information and associated algorithms to predistort the signal, allowing the PA to correct the predistortion, resulting in high linearity. When hardware is used to generate the predistortion, the predistorting transfer characteristic must be determined, and appropriate hardware must be developed. There are no algorithms or methods to accomplish this, so it can be a formidable task. In either case, the improvements in linearity are limited by the lack of any feedback to allow for deviations from the intended operation, and by the ability to actually determine and create the required predistortion. In short, it is cheap, but don’t expect dramatic results!
Electronic Circuits in Action
Published in Trevor Linsley, Electronic Servicing and Repairs, 2014
When an amplifier is used to amplify the input voltage or current in such a way that the output is an enlarged copy of the input and is not distorted, it is said to be a small signal amplifier. When an amplifier is used to amplify the power of an input signal it is said to be a power amplifier.Figure 5.26 shows the circuit diagram of an audio frequency amplifier. The left-hand side of the circuit, the op amp, is a small signal voltage amplifier which is used to amplify a small signal from, for example, the ear piece jack plug of a tape recorder. The right-hand side of the circuit is the power amplifier which is required to drive the speaker. This is made from a pair of complementary power transistors, one is an n-p-n and the other a p-n-p transistor which have beenmatched so that they have the same gain and other properties. When the voltage on the top transistor is positive the voltage on the bottom transistor is negative and vice versa. The amplification of each half of the voltage waveform is, therefore, shared between the two transistors. A circuit which is constructed in this way is known as a push-pull amplifier. The additional power required to drive the speaker in this circuit comes from the 9 V batteries.
Speakers and amps
Published in Trev Wilkins, Access All Areas, 2012
Our sound source is radiating all these frequencies, which are being picked up by a microphone. This piece of gear absorbs the vibrations and turns them into a small electrical current known as an audio signal, which can be sent down a wire to an amplifier. The amplifier will receive a very small impression of the sound that is too minute to drive a speaker but that is a pretty good representation of the real sound (if it's a good microphone). The amplifier takes this signal and increases it by using a high electrical current to reproduce it at a level sufficient to drive a speaker. Smaller amplifiers called ‘pre-amplifiers’ (preamps)may first increase the signal and then pass it on to power amplifiers. Mixing consoles contain pre-amps that send a workable signal through their own circuits, then pass it down the line to the power amplifiers. In essence, the amplifier increases the ‘amplitude’ or level of the signal. We perceive amplitude as how loud something is, so imagine that the microphone is sending a very quiet sound level that the amplifier makes louder.
Design and implementation of 75~110 GHz elliptical dual balun in 90 nm CMOS for W-Band transceiver
Published in International Journal of Electronics, 2019
Thanks to the swift evolution of CMOS technology (Lin et al., 2010), now it is widely used to implement radio-frequency integrated circuits (RFICs) for millimeter-wave (MMW) communication systems, such as 77 GHz automotive radars (Lin, Wen, & Wang, 2014), 94 GHz imaging radars (Lin, Lan, Wang, Chi, & Lu, 2016), and 210 GHz chip-to-chip communication (Moghadami, Hajilou, Agrawal, & Ardalan, 2015). In transmitter design, power amplifier (PA) is a key component which amplifies the up-converted (or modulated) IF signals to the requested power level over the RF band of interest. To meet the output power (Pout) specification of PAs, multi-way architecture is usually adopted (Law & Pham, 2010; Lin & Nguyen, 2017). In multi-way PA, power splitter and combiner are commonly used (Boccia, Emanuele, Shamsafar, Amieri, and Amendola 2015; Babu, Singh, & Jha, 2005). The basic requirements of a PA include fine impedance matching at the input and output ports, high power gain, high Pout and linearity, and high power-added efficiency (PAE) over the operation band. Figure 1(a) shows the block diagram of a conventional four-way PA for achieving high Pout (Law & Pham, 2010). The PA unit is normally a three-stage cascaded amplifier, which includes input, driving and output stages (see Figure 2(b)). In addition, a four-way Wilkinson power splitter, which is composed of three two-way Wilkinson power splitters (Hawatmeh, Shamaileh, Dib, & Sheta, 2013; Hazeri, 2012), is needed to averagely split the input signals into four ways. A four- way Wilkinson power combiner, which is composed of three two-way Wilkinson power combiners, is required for combining the amplified signals by the four PA units into a single output. For comparison, a W-band four-way Wilkinson power splitter is designed. Its chip size is 0.35 mm× 0.5 mm (i.e. 0.175 mm2), as shown in Figure 1(b). The large chip size (i.e. long transmission line (TL)) of the four-way Wilkinson power splitter and combiner in the PA normally leads to ungratified Pout and PAE.