Switching speed

Switching speed. Typical switching times for TN devices are 20 to 50ms, which is quite slow and has limited tl television displays. 

The frequency response or switching speed of the bipolar transistor is governed by the same processes which control the speed of thep—n junction, the capacitance associated with the movement of charge into and out of the depletion regions. To achieve high frequencies the dimensions of the active areas and parasitic circuit elements must be reduced. The two critical dimensions are the width of the emitter contact and the base thickness, W. The cutoff frequency,, is the frequency at which = 57 / - b /t > where is the emitter-to-coUector delay time and is the sum of the emitter... 

Far instrumentation purposes, there are clear advantages in placing at least some of the electronic circuitry close to the sensor (see Section 15.1) in order to reduce pick-up noise. However, there may also be inherent advantages in operating transistors at low temperatures, such as increased switching speed or lower noise. A serious problem is the effect on device reliability of the stresses induced by thermal cycling. 

Gold has been used for many years as a minority carrier lifeline controller in Si. As such, it is introduced in a controlled manner, usually by diffusion into transistor structures to decrease the carrier lifetime in the base region in order to increase the switching speed (Ravi, 1981). Conversely, the uncontrolled presence of Au is clearly deleterious to the performance of devices, both because of the increased recombination within the structure and the increase of pipe defects, which can cause shorting of the device. These pipe defects consist of clusters of metallic impurities at dislocations bounding epitaxial stacking faults. 

Grant et al. (2002) designed a parallel system employing two HTLC columns (Cyclone, 50 x 1 mm, Cohesive Technologies) connected to one analytical column (Zorbax SB-C18, 50 x 2 mm, Hewlett Packard) on a 2300 HTLC. A polyarylethyl ketone (PAEK) six-port Valeo (Valeo Instruments, Texas) was used to increase switching speed and reduce carry-over. Peak focusing was used when the analyte was flushed from the TFC column into the analytical column by aqueous dilution. Compared to the dual column method, the overall time reduction was 1.5 to 4 min per sample with comparable data quality at the linear range of 0.1 to 100 ng/mL. 

The poly(I)-based transistor is the first illustration of a microelectrochemical transistor based on a combination of a conducting and a conventional redox polymer as the active material. The transistor "turns on" at VG corresponding to oxidation of the polythiophene backbone. The resistivity of poly(I) declines by a factor of 105 upon changing VG from 0.4 V to 0.8 V vs. Ag+/Ag. When Vg is moved close to the one-electron reduction potential of V2+/+, the conventional redox conductivity gives a small degree of "turn on". A sharp Iq-Vq characteristic results, with an Ip(peak) at Vq = E° (V2+/+). Though the microelectrochemical devices based on conventional redox conduction have both slow switching speed and a... 

Wide 160 degree viewing angle High printable ink-like characteristics High, microseconds. Video enabling. Slower switching speeds (100 p.s) for LEC architectures >10,000... 

In this 0-switching technique, one of the cavity mirrors is effectively removed during pumping and then suddenly replaced. The build-up time of the giant pulse is determined by the switching speed and the initial gain of the pumped laser. 

For low-power applications, the devices of choice are the MOSFET, the IGBT, and the BJT. For applications up to 1 kV, the MOSFET is the device of choice because it is a voltage-control device and has a fast switching speed. For applications ranging in voltage from 1 kV up to 4 kV, the IGBT is most often used. The thyristor and the GTO are used for voltages over 4 kV. 

When designing digital circuits we are concerned with how different circuit elements affect the operation of the circuit. In this section we will look at switching speed. First, we will look at a basic BJT inverter and observe its operation. Wire the circuit below ... 

EXERCISE 6-15 For the BJT inverter, run the circuit to observe how Rb affects switching speed. Let RC remain constant at 1 kQ. 

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