Avalanche Transistor


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avalanche transistor

[′av·ə‚lanch tran′zis·tər]
(electronics)
A transistor that utilizes avalanche breakdown to produce chain generation of charge-carrying hole-electron pairs.

Avalanche Transistor

 

a transistor that operates stably at collector junction voltages approaching the breakdown voltage. Under such conditions, collision ionization occurs, leading to an increase in the number of charge carriers in the collector junction of the transistor. Stable operation of avalanche transistors in the near-breakdown region is due to the greater uniformity of electric field distribution over the area of the collector junction. Avalanche transistors are manufactured using epitaxial p+-p and n +-n structures; the base region of the transistor is produced by diffusion methods.

Peculiarities of avalanche transistors are the possibility of obtaining a negative resistance in the emitter-collector circuit and the rapid current buildup in the circuit. Avalanche transistors are used in generators of short pulses with a steep front; they make relatively simple the shaping of powerful current pulses (up to several amperes) with a pulse rise time of less than 10–9 sec. The possibility of generation by avalanche transistors of short pulses with a repetition frequency of up to 100 megahertz is used in coincidence circuits and sampling oscilloscopes. The existence of a region of negative resistance in the current-voltage characteristic of an avalanche transistor and the low effective value of the charge carrier transit time (from emitter to collector) make possible the use of such transistors in oscillators and amplifiers of electric oscillations in the decimeter and centimeter wavelength bands.

IU. A. KUZNETSOV

References in periodicals archive ?
Noise level ([T.sub.n] and ENR) for the avalanche transistor circuit is compared with some other noise sources in Table I.
To demonstrate the mechanism behind the observed random pulses in the avalanche transistor circuit, we propose a phenomenological analog model, which is presented in Fig.
The subcircuit C2-R4-L-C3-R5 is inserted in the model circuit to imitate the inertial properties of the avalanche transistor. The values of the elements of the circuit in Fig.
Figure 6 shows a typical impulse generator circuit using an avalanche transistor. Short impulses will be generated when the trigger source excites the base of the transistor.
TABLE I TYPE OF PULSE SOURCES AND THEIR CHARACTERISTICS (5) Best Available Risetime at Type Step/Pulse Amplitude Notes Mercury switch step 70 ps 300 V max PRF = 200 Hz Avalanche transistor pulse 150 ps 12 V device selection necessary Tunnel diode step 25 ps 0.25 V fastest transition time 100 ps 1.0 V 60 ps 20 V commercially available Step recovery step 100 ps 50 V specially ordered 200 ps 200 V four-stack Avalanche diode impulse 400 ps 125 V MHz rep.
Based on the best available rise time at amplitude in Table 1, it is clear that avalanche transistors, tunnel diodes and step recovery diodes are the best choices for low power ultra-short pulse generation.
Moreover, particular instances of the subcomponents and methodologies were also known -- avalanche transistor switches, light responsive switches, use of subcarriers in coding pulse trains, leading edge detectors, ring demodulators, monostable multi-vibrator detectors, integration and averaging matched filters, template signal match detectors, correlation d etectors, signal integrators, synchronous detectors and antennas driven by a stepped amplitude input.
TYPICAL CHARACTERISTICS OF PULSE SOURCES Type Step-Pulse Best Available Risetime at Amplitude Mercury switch step 70 ps 300 V Avalanche transistor pulse 150 ps 12 V Tunnel diode step 25 ps 0.25 V 100 ps 1.0 V 60 ps 20 V Step recovery step 100 ps 50 V 200 ps 200 V Hertzian impulse; also 100 ps 1000 V pulse modulated 1 ns 1000 V Avalanche diode impulse 400 ps 125 V Type Notes Mercury switch max PRF = 200 Hz Avalanche transistor device selection necessary Tunnel diode fastest transition time commercially available Step recovery specially ordered four-stack Hertzian limited lifetime, sparkgap Avalanche diode Megahertz repitition rate
A simple method of generating UWB signals is to use avalanche transistors and has been known for many years.