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Semiconductor Devices
Published in Dale R. Patrick, Stephen W. Fardo, Electricity and Electronics Fundamentals, 2020
Dale R. Patrick, Stephen W. Fardo
In an ordinary junction diode, the depletion region is an area which separates the P and N material on each side of the junction. This area develops when the junction is initially formed. It represents a unique part of the diode that is essentially void of current carriers. In this regard, the depletion region serves as a dielectric medium or insulator. When a diode has bias voltage applied, its depletion region will change in width. In a sense, this means that a diode responds as a voltage-variable capacitor. By definition, a capacitor is two or more conductors separated by an insulating material. The P and N materials, being semiconductors, are separated by a depletion region insulator. Devices designed to respond to the capacitance effect are called varactors, varicap diodes, or voltage-variable capacitors.
Conversion
Published in John Watkinson, An Introduction to Digital Audio, 2013
If an external clock source is provided, it cannot be used directly, but must be fed through a well-designed, well-damped phase-locked loop which will filter out the jitter. The operation of a phase-locked loop was described in Chapter 3. The phase-locked loop must be built to a higher accuracy standard than in most applications. Noise reaching the frequency control element will cause the very jitter the device is meant to eliminate. Some designs use a crystal oscillator whose natural frequency can be shifted slightly by a varicap diode. The high Q of the crystal produces a cleaner clock. Unfortunately this high Q also means that the frequency swing which can be achieved is quite small. It is sufficient for locking to a single standard sampling rate reference, but not for locking to a range of sampling rates or for variable-speed operation. In this case a conventional varicap VCO is required.
Conversion
Published in John Watkinson, The Art of Digital Audio, 2013
If an external clock source is used, it cannot be used directly, but must be fed through a well-designed, well-damped phase-locked loop which will filter out the jitter. The operation of a phase-locked loop was described in Chapter 2. The phase-locked loop must be built to a higher accuracy standard than in most applications. Noise reaching the frequency control element will cause the very jitter the device is meant to eliminate. Some designs use a crystal oscillator whose natural frequency can be shifted slightly by a varicap diode. The high Q of the crystal produces a cleaner clock. Unfortunately this high Q also means that the frequency swing which can be achieved is quite small. It is sufficient for locking to a single standard sampling rate reference, but not for locking to a range of sampling rates or for variable-speed operation. In this case a conventional varicap VCO is required. Some machines can switch between a crystal VCO and a wideband VCO depending on the sampling rate accuracy. As will be seen in Chapter 8, the AES/EBU interface has provision for conveying sampling rate accuracy in the channel status data and this could be used to select the appropriate oscillator. Some machines which need to operate at variable speed but with the highest quality use a double-phase-locked loop arrangement where the residual jitter in the first loop is further reduced by the second. The external clock signal is sometimes fed into the clean circuitry using an optical coupler to improve isolation.
Circuit-based versus full-wave modelling of active microwave circuits
Published in International Journal of Electronics, 2018
Branko Bukvić, Andjelija Ž. Ilić, Milan M. Ilić
First, note that two non-linear components are incorporated in the design: a Cree CGH40010F gallium-nitride (GaN) high-electron-mobility transistor and a varicap diode NXP BB179 in the input matching network (which provides tunability). We assume the non-linear transistor model to be sufficiently accurate; the operating regime in the linear class AB and the recorded electrode signals did not exceed the range of parameters where the model validity was defined and tested. Thus, we can analyse the discrepancies between measurements and circuit simulations, which are too often attributed mainly to inaccurate modelling of non-linear components. This is one of the issues to be addressed.