Memory switching diode
The memory switching diode , charge storage diode or tear -off diode ( English step recovery diode , SRD, also English snap-off diode ) is a semiconductor diode with a long service life for the minority charge carriers . If the polarity of a memory switching diode is reversed from the forward direction to the reverse direction, flows for a defined time (approx. 0.1 nsup to 3 ns) a current in reverse direction without the voltage at the diode changing significantly. Only then, when the free charge carriers have been used up, does the current suddenly collapse and the voltage applied to the diode can very quickly assume high values in the reverse direction, as shown in the adjacent time diagram.
Due to the sudden switch from an almost ideal short circuit to the blocking behavior, a sinusoidal voltage applied to the diodes is distorted in a strongly non-linear manner and harmonics arise . These harmonics can be eliminated by suitable downstream filter stages . Memory switching diodes with a short switch-off time are therefore used to multiply frequencies in the range from approx. 1 GHz upwards. The memory switching diode also has applications in pulse shaping, e.g. B. the generation of sharp pulse edges or short pulses for input signals with a comparatively slow rise or fall in voltage. The shortest pulses that can be generated in this way are approx. 100 ps long.
Memory switching diodes are usually constructed with a pin structure like PIN diodes . The small thickness of the intrinsically ( intrinsically conductive) i-layer and the resulting high electric field in the i-layer are the cause of the rapid disappearance of the minority charge carriers when the current direction changes. The lifetime of the minority charge carriers without an applied field is, however, much longer, on the order of 100 ns. Because of the thin i-layer, most memory switching diodes have relatively low permissible reverse voltages, usually below 100 V.
In principle, every semiconductor diode with a pn junction is a memory switching diode because the minority charge carriers remain in the space charge zone for a certain period of time after polarity reversal - in contrast to Schottky diodes , where the charge is only transported by majority charge carriers . With most other types of semiconductor diodes, especially the rectifier diodes for high frequencies, care is taken to keep the reverse recovery time as short as possible ( English fast-recovery diode ).
The first memory switching diodes were developed in the early 1960s and were among the fastest components in semiconductor technology for a long time .
Current manufacturers of memory switching diodes are ASI-Semiconductor, MicroSemi, M-Pulse and Macom.
use
- Comb generator
- Harmonic generator
- Voltage controlled oscillator
- Frequency multiplier
- Sampling phase detector
literature
- Hewlett-Packard: Pulse and Waveform Generation with Step Recovery Diodes, Application Note 918 . Palo Alto 1984 ( Online [PDF; 2.9 MB ]).