Introduction to Crystal Diodes 6

It is a tuning signal source that utilizes the variable capacitance characteristics of a varactor to tune the frequency of local oscillation (referred to as local oscillation in television receiver tuners). Figure 8 (b) shows a sawtooth oscillator composed of a varactor, a single junction transistor, and a constant current diode, which uses the output signal for frequency modulation. Since most varactor transistors operate under reverse bias, constant current protection should be added to prevent breakdown.

6. Step recovery diode

A step recovery diode is a special type of varactor, also known as a charge storage diode, abbreviated as a step recovery diode. It has a highly nonlinear reactance and is unique to the era of frequency multipliers. By utilizing the rich harmonics contained in the rapid change of reverse recovery current, it can achieve high-efficiency high-order frequency doubling. It is an excellent frequency doubling component in the microwave field.

The characteristic of a stage transistor is that when a diode in a conducting state suddenly applies a reverse voltage, the instantaneous reverse current immediately reaches the maximum value IR and maintains it for a certain period of time ts, and the junction difference immediately returns to zero. The relationship between current and time

Step transistors are mainly used in frequency doubling circuits and ultra high speed pulse shaping and generation circuits. Figure 11 (a) is a curved high-order frequency converter, and using a step transistor, it is easy to achieve up to 20 times frequency doubling while maintaining high efficiency. Figure 11 (b) shows a pulse shaping circuit using a step transistor, and Figure 11 (c) compares the waveforms before and after shaping.diode