Step-Recovery Diode: It differs from the fast recovery diode. Its main feature is that the falling time tf at turn-off is almost 0 (on the order of ps), but its storage time ts is relatively long. The high recovery switch of the fast recovery diode has a short storage time and a fall time, so the total reverse recovery time is short. However, the measures taken in achieving a short reverse recovery time are mainly focused on reducing the storage time, and the fall time often has a certain influence on the switching performance (ie, the reverse current waveform at the time of shutdown has a certain Trailing).

The step diode is also called a step recovery diode, and the reverse recovery time trr when switching from on to off is short, and therefore, the transfer time in which the characteristic is rapidly turned off is remarkably short. If a sine wave is applied to the step diode, since the tt (transfer time) is short, the output waveform is suddenly pinched off, so that many high-frequency harmonics can be generated. It is also a diode with a PN junction. Its structural characteristics are: there is a steep impurity distribution area at the boundary of the PN junction, thereby forming a "self-service electric field". Since the PN junction is under forwarding bias, it conducts with minority carriers and has a charge storage effect near the PN junction, so that its reverse current needs to undergo a "storage time" before it can be reduced to a minimum (reverse Saturation current value).

The step recovery diode is a special varactor, also known as a charge storage diode. It is called a step tube. It has a highly nonlinear reactance and is used in the unique characteristics of the frequency multiplier era. The rich harmonics contained in the rapid mutation can achieve high efficiency and high-frequency multiplication, which is an excellent frequency doubling component in the microwave field.

characteristic

The characteristics of the step recovery diode: after the stored charge disappears (at t = ts), the reverse current suddenly drops to zero, which eliminates the reverse current tailing at turn-off. This diode not only has a very short fall time but also has good forward conductivity. Because of this good forward conductivity, it will store a large amount of minority carrier charge at the forward voltage, and the storage time for the shutdown is also longer. Since the step recovery diode will store a large amount of minority carrier charge during forwarding operation, it is a good so-called charge storage diode.

How to achieve the fall time tf≈0 of the step recovery diode during the turn-off process? The basic consideration should be that the minority carrier concentration gradient at the edge of the p-n junction barrier region needs to become zero when the storage time ts is over. This can be achieved by providing a built-in electric field in the diffusion region from the barrier region to the diffusion region. Because the built-in electric field in this direction has an acceleration effect on the forward diffusion of minority carriers, it has a blocking effect on the reverse diffusion, that is, it has the potential to hold the minority carriers when the PN junction is turned off. They flow into the barrier zone; in this way, the minority carrier concentration at the edge of the barrier region cannot become zero until all stored minority carriers disappear, so dp/dx= 0, that is, the reverse diffusion current quickly drops to 0, so the fall time tf ≈ 0.

The built-in electric field in the step recovery diode can be introduced by a non-uniform doping technique. In fact, the diode is often structurally a P-I-N junction with a very steep doping concentration distribution near the interface (usually formed by epitaxial techniques). Because the step recovery diode has this special impurity concentration distribution similar to that of a varactor, the diode can also be considered as a special varactor.

How to make a step recovery diode? The Si used is often a material with a long carrier lifetime (0.5 to 5 μs) to obtain more storage charges. To reduce the storage time when manufacturing a fast recovery diode, the Si material used. The minority carrier lifetime is very short (approximately 1000 times shorter than the step recovery diode).

The DC volt-ampere characteristics of the step recovery diode are the same as those of a typical p-n junction; in general, the forward voltage drop is low and the reverse breakdown voltage is high (using the P-I-N structure). However, it is very special in transient response. Because of its falling time ≈0, the current changes during turn-off is very fast (the current waveform is steep), so it is a kind of reactive component with highly nonlinear characteristics, so in circuit applications. It can produce rich harmonic components. Thus, step recovery diodes can be used for frequency multipliers, high-speed pulse shaping, and generators, and high-frequency harmonic generators. When used as a frequency multiplier, it can maintain high efficiency in up to 20 times of multiplier, so it is an excellent microwave frequency doubling component.

Of course, if it can be achieved not only that the storage time is short, but also that the fall time is approximately zero like a step recovery diode, the diode is inevitably an extremely excellent ultra-high-speed switching diode.

How the step recovery diode works

The step diode is also called a step recovery diode, and the reverse recovery time trr when switching from on to off is short, and therefore, the transfer time in which the characteristic is rapidly turned off is remarkably short. If a sine wave is applied to the step diode, since the tt (transfer time) is short, the output waveform is suddenly pinched off, so that many high-frequency harmonics can be generated. It is also a diode with a PN junction. Its structural characteristics are: there is a steep impurity distribution area at the boundary of the PN junction, thereby forming a "self-service electric field". Since the PN junction is under forwarding bias, it conducts with minority carriers and has a charge storage effect near the PN junction, so that its reverse current needs to undergo a "storage time" before it can be reduced to a minimum (reverse Saturation current value).

The step recovery diode is a special varactor, also known as a charge storage diode. It is called a step tube. It has a highly nonlinear reactance and is used in the unique characteristics of the frequency multiplier era. The rich harmonics contained in the rapid mutation can achieve high efficiency and high-frequency multiplication, which is an excellent frequency doubling component in the microwave field.

The characteristics of the step tube are based on the special distribution of the PN junction impurity, similar to the varactor tube. The symbol of the step tube is shown in Figure 1. Its DC volt-ampere characteristics are the same as those of the general PN structure.

The characteristics of the step dioide:

The "self-service electric field" of the step recovery diode shortens the storage time, allows the reverse current to be quickly turned off, and produces rich harmonic components. A comb spectrum generation circuit can be designed using these harmonic components. Fast turn-off (step recovery) diodes are used in pulse and higher harmonic circuits.

When the diode in the on state suddenly adds a reverse voltage, the instantaneous reverse current immediately reaches the maximum value IR and maintains a certain time ts, and the difference immediately returns to zero.

Step tube application